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BASH(1)"1991 November 24" GNU

NAME
bash - GNU Bourne-Again SHell

SYNOPSIS
bash [options] [file]

COPYRIGHT
Copyright (C) 1989, 1991 by the Free Software Foundation, Inc.

DESCRIPTION
Bash is an sh-compatible command language interpreter that executes
commands read from the standard input or from a file. Bash also
incorporates useful features from the Korn and C shells (ksh and
csh).

Bash is ultimately intended to be a faithful implementation of the
IEEE Posix Shell and Tools specification (IEEE Working Group
1003.2).

OPTIONS
In addition to the single-character shell options documented in the
description of the set builtin command, bash interprets the follow-
ing flags when it is invoked:


-c string If the -c flag is present, then commands are read from
string.

-i If the -i flag is present, the shell is interactive.

-s If the -s flag is present, or if no arguments remain after op-
tion processing, then commands are read from the standard in-
put. This option allows the positional parameters to be set
when invoking an interactive shell.

- A single - signals the end of options and disables further op-
tion processing. Any arguments after the - are treated as
filenames and arguments. An argument of -- is equivalent to
an argument of -.

Bash also interprets a number of multi-character options. These
options must appear on the command line before the single-character
options to be recognized.


-norc Do not load the personal initialization file ~/.bashrc if
the shell is interactive. This is the default if the
shell name is sh.

-noprofile
Do not read either /etc/profile or ~/.bash_profile. By de-
fault, bash normally reads these files when it is invoked as a
login shell.

-rcfile file
Execute commands from file instead of the standard personal
initialization file ~/.bashrc, if the shell is interactive.

-version
Show the version number of this instance of bash when start-
ing.

-quiet
Do not be verbose when starting up (do not show the shell ver-
sion or any other information).

-login
Make bash act as if it had been invoked by login(1).

-nobraceexpansion
Do not perform curly brace expansion a la csh.

-nolineediting
Do not use the GNU readline library to read command lines if
interactive.

ARGUMENTS
If arguments remain after option processing, and neither the -c nor
the -s option has been supplied, the first argument is assumed to
be the name of a file containing shell commands. If bash is in-
voked in this fashion, $0 is set to the name of the file, and the
positional parameters are set to the remaining arguments. Bash
reads and executes commands from this file, then exits.

DEFINITIONS

blank A
space or tab.

word A sequence of characters considered as a single unit by the
shell. Also known as a token.

name A word consisting only of alphanumeric characters and under-
scores, and beginning with an alphabetic character or an un-
derscore. Also referred to as an identifier.

metacharacter
A character that, when unquoted, separates words. One of the
following:

| & ; ( ) < >


control operator
A token that performs a control function. It is one of the
following symbols:

|| & && ; ;; ( ) |

"RESERVED WORDS"
Reserved words are words that have a special meaning to the shell.
The following words are recognized as reserved when unquoted and
either the first word of a simple command (see SHELL GRAMMAR below)
or the third word of a case or for command:

! case do done elif else esac fi for function if in then until
while { }

"SHELL GRAMMAR"

Simple Commands

A simple command is a sequence of optional variable assignments
followed by blank-separated words and redirections, and terminated
by a control operator. The first word specifies the command to be
executed. The remaining words are passed as arguments to the in-
voked command.

The return value of a simple command is its exit status, or 128+n
if the command is terminated by signal n.

Pipelines

A pipeline is a sequence of one or more commands separated by the
character |. The format for a pipeline is:

[ ! ] command [ | command2 ... ]

The standard output of command is connected to the standard input
of command2. This connection is performed before any redirections
specified by the command (see REDIRECTION below).

If the reserved word ! precedes a pipeline, the exit status of that
pipeline is the logical NOT of the exit status of the last command.
Otherwise, the status of the pipeline is the exit status of the
last command. The shell waits for all commands in the pipeline to
terminate before returning a value.

Each command in a pipeline is executed as a separate process (i.e.
in a subshell).

Lists

A list is a sequence of one or more pipelines separated by one of
the operators ;, &, &&, or bvbv, and optionally terminated by one
of ;, &, or .

Of these list operators, && has highest precedence. bvbv has the
next highest precedence, followed by ; and &, which have equal
precedence.

If a command is terminated by the control operator &, the shell ex-
ecutes the command in the background in a subshell. The shell does
not wait for the command to finish. Commands separated by a ; are
executed sequentially; the shell waits for each command to termi-
nate in turn.

The control operators && and bvbv denote AND lists and OR lists,
respectively. An AND list has the form

command && command2

command2 is executed if, and only if, command returns an exit sta-
tus of zero.

An OR list has the form

command bvbv command2


command2 is executed if and only if command returns a non-zero exit
status.

Compound Commands

A compound command is one of the following:

(list)
list is executed in a subshell. Variable assignments and
builtin commands that affect the shell's environment do not
remain in effect after the command completes.

{ list; }
list is simply executed in the current shell environment.
This is known as a group command.

for name [ in word; ] do list ; done
The list of words following in is expanded, generating a list
of items. The variable name is set to each element of this
list in turn, and list is executed each time. If the in word
is omitted, the for command executes list once for each posi-
tional parameter that is set (see PARAMETERS below). The exit
status is the exit status of the last command, or zero if no
commands were executed.

case word in [ pattern [ | pattern ] ) list ;; ] ... esac
A case command first expands word, and tries to match it
against each pattern in turn. When a match is found, the cor-
responding list is executed. After the first match, no subse-
quent matches are attempted. The exit status is zero if no
patterns are matches. Otherwise, it is the exit status of the
last command executed in list.

if list then list [ elif list then list ] ... [ else list ] fi
The if list is executed. If its exit status is zero, the then
list is executed. Otherwise, each elif list is executed in
turn, and if its exit status is zero, the corresponding then
list is executed and the command completes. Otherwise, the
else list is executed, if present. The exit status is the
exit status of the last command executed, or zero if no condi-
tion tested true.

while
list do list done

until list do list done
The while command continuously executes the do list as long as
the last command in list returns an exit status of zero. The
until command is identical to the while command, except that
the test is negated; the do list is executed as long as the
last command in list returns a non-zero exit status. The exit
status of the while and until commands is the exit status of
the last do list command executed, or zero if none was exe-
cuted.

[ function ] name () { list; }
This defines a function named name. The body of the function
is the list of commands between { and }. This list is executed
whenever name is specified as the name of a simple command.
The exit status of a function is the exit status of the last
command executed in the body. (See FUNCTIONS below.)

COMMENTS
In a non-interactive shell, a word beginning with # causes that
word and all remaining characters on that line to be ignored.

QUOTING
Quoting is used to remove the special meaning of certain characters
or words to the shell. Quoting can be used to disable special
treatment for special characters, to prevent reserved words from
being recognized as such, and to prevent parameter expansion.

Each of the metacharacters listed above under DEFINITIONS has spe-
cial meaning to the shell and must be quoted if they are to repre-
sent themselves. There are three quoting mechanisms: the escape
character, single quotes, and double quotes.

A non-quoted backslash () is the escape character. It preserves
the literal value of the next character that follows, with the ex-
ception of . If a pair appears, it is treated
as a line continuation (that is, it is effectively ignored), if the
backslash is non-quoted.

Enclosing characters in single quotes preserves the literal value
of each character within the quotes. A single quote may not occur
between single quotes, even when preceded by a backslash.

Enclosing characters in double quotes preserves the literal value
of all characters within the quotes, with the exception of $, `,
and . The characters $ and ` retain their special meaning within
double quotes. The backslash retains its special meaning only when
followed by one of the following characters: $, `, ", , or line>. A double quote may be quoted within double quotes by pre-
ceding it with a backslash.

The special parameters * and @ have special meaning when in double
quotes (see PARAMETERS below).

PARAMETERS
A parameter is an entity that stores values, somewhat like a vari-
able in a conventional programming language. It can be a name, a
number, or one of the special characters listed below under Spe-
cial Parameters. For the shell's purposes, a variable is a parame-
ter denoted by a name.

A parameter is set if it has been assigned a value. The null
string is a valid value. Once a variable is set, it may be unset
only by using the unset builtin command (see SHELL BUILTIN COMMANDS
below).

A variable may be assigned to by a statement of the form

name=[value]

If value is not given, the variable is assigned the null string.
All values undergo tilde expansion, parameter and variable expan-
sion, command substitution, arithmetic expansion, and quote re-
moval. If the variable has its -i attribute set (see declare below
in SHELL BUILTIN COMMANDS) then value is subject to arithmetic ex-
pansion even if the $[...] syntax does not appear. Word splitting
is not performed, with the exception of "[email protected]" as explained below un-
der Special Parameters. Pathname expansion is not performed.

Positional Parameters

A positional parameter is a parameter denoted by one or more dig-
its, other than the single digit 0. Positional parameters are as-
signed from the shell's arguments when it is invoked, and may be
reassigned using the set builtin command. The positional parame-
ters are temporarily replaced when a shell function is executed
(see FUNCTIONS below).

When a positional parameter consisting of more than a single digit
is expanded, it must be enclosed in braces (see EXPANSION below).

Special Parameters

The shell treats several parameters specially. These parameters
may only be referenced; assignment to them is not allowed.

* Expands to the positional parameters, starting from one. When
the expansion occurs within double quotes, it expands to a
single word with the value of each parameter separated by the
first character of the IFS special variable. That is, ``$*''
is equivalent to ``$1c$2c...'', where c is the first character
of the value of the IFS variable. If IFS is null or unset,
the parameters are separated by spaces.

@ Expands to the positional parameters, starting from one. When
the expansion occurs within double quotes, each parameter ex-
pands as a separate word. That is, `` [email protected]'' is equivalent to
``$1'' ``$2'' ... When there are no positional parameters,
``[email protected]'' and [email protected] expand to nothing (i.e. they are removed).

# Expands to the number of positional parameters in decimal.

? Expands to the status of the most recently executed foreground
pipeline.

- Expands to the current option flags as specified upon invoca-
tion, by the set builtin command, or those set by the shell
itself (such as the -i flag).

$ Expands to the process ID of the shell. In a () subshell, it
expands to the process ID of the current shell, not the sub-
shell.

! Expands to the process ID of the most recently executed back-
ground (asynchronous) command.

0 Expands to the name of the shell or shell script. This is set
at shell initialization. If bash is invoked with a file of
commands, $0 is set to the name of that file. Otherwise, it
is set to the pathname used to invoke bash, as given by argu-
ment zero.

_ Expands to the last argument to the previous command, after
expansion. Also set to the full pathname of each command exe-
cuted and placed in the environment exported to that command.

Shell Variables

The following variables are set by the shell:


PPID The process ID of the shell's parent.

PWD The current working directory as set by the cd command.

OLDPWD
The previous working directory as set by the cd command.

REPLY
Set to the line of input read by the read builtin command when
no arguments are supplied.

UID Expands to the user ID of the current user.

EUID Expands to the effective user ID of the current user.

BASH Expands to the full pathname used to invoke this instance of
bash.

BASH_VERSION
Expands to the version number of this instance of bash.

SHLVL
Incremented by one each time an instance of bash is started.

RANDOM
Each time this parameter is referenced, a random integer is
generated. The sequence of random numbers may be initialized
by assigning a value to RANDOM. If RANDOM is unset, it loses
its special properties, even if it is subsequently reset.

SECONDS
Each time this parameter is referenced, the number of seconds
since shell invocation is returned. If a value is assigned to
SECONDS, the value returned upon subsequent references is the
number of seconds since the assignment plus the value as-
signed. If SECONDS is unset, it loses its special properties,
even if it is subsequently reset.

LINENO
Each time this parameter is referenced, the shell substitutes
a decimal number representing the current sequential line num-
ber (starting with 1) within a script or function. When not
in a script or function, the value substituted is not guaran-
teed to be meaningful. When in a function, the value is not
the number of the source line that the command appears on
(that information has been lost by the time the function is
executed), but is an approximation of the number of simple
commands executed in the current function. If LINENO is un-
set, it loses its special properties, even if it is subse-
quently reset.

OPTARG
The value of the last option argument processed by the getopts
builtin command (see SHELL BUILTIN COMMANDS below).

OPTIND
The index of the last option processed by the getopts builtin
command (see SHELL BUILTIN COMMANDS below).

The following variables are used by the shell. In some cases, bash
assigns a default value to a variable; these cases are noted below.


IFS The Internal Field Separator that is used for word splitting
after expansion and to split lines into words with the read
builtin command. The default value is `` line>''.

PATH The search path for commands. It is a colon-separated list of
directories in which the shell looks for commands (see COMMAND
EXECUTION below). The default path is system-dependent, and
is set by the administrator who installs bash. A common value
is ``.:/usr/gnu/bin:/usr/lo-
cal/bin:/usr/ucb:/bin:/usr/bin:/etc:/usr/etc''. Note that in
some circumstances, however, a leading `.' in PATH can be a
security hazard.

HOME The home directory of the current user; the default argument
for the cd builtin command.

CDPATH
The search path for the cd command. This is a colon-separated
list of directories in which the shell looks for destination
directories specified by the cd command. A sample value is
``.:~:/usr''.

ENV If this parameter is set when bash is executing a shell
script, its value is interpreted as a filename containing com-
mands to initialize the shell, as in .bashrc. The value of
ENV is subjected to parameter expansion, command substitution,
and arithmetic expansion before being interpreted as a path-
name. PATH is not used to search for the resultant pathname.

MAIL If this parameter is set to a filename and the MAILPATH vari-
able is not set, bash informs the user of the arrival of mail
in the specified file.

MAILCHECK
Specifies how often (in seconds) bash checks for mail. The
default is 60 seconds. When it is time to check for mail, the
shell does so before prompting. If this variable is unset,
the shell disables mail checking.

MAILPATH
A colon-separated list of pathnames to be checked for mail.
The message to be printed may be specified by separating the
pathname from the message with a `?'. $_ stands for the name
of the current mailfile. Example:

MAILPATH='/usr/spool/mail/bfox?"You have mail":~/shell-mail?"$_ has
mail!"'

Bash supplies a default value for this variable, but the location
of the user mail files that it uses is system dependent (e.g.
/usr/spool/mail/$USER).

MAIL_WARNING
If set, and a file that bash is checking for mail has been ac-
cessed since the last time it was checked, the message ``The
mail in` mailfile has been read'' is printed.

PS1 The value of this parameter is expanded (see PROMPTING below)
and used as the primary prompt string. The default value is
``bash$ ''.

PS2 The value of this parameter is expanded like PS1 and used as
the secondary prompt string. The default is ``> ''.

PS4 The value of this parameter is expanded like PS1 and the value
is printed before each command bash displays during an execu-
tion trace. The first character of PS4 is replicated multiple
times, as necessary, to indicate multiple levels of indirec-
tion. The default is ``+ ''.

NO_PROMPT_VARS
If set, the decoded prompt string does not undergo further ex-
pansion (see PROMPTING below).

HISTSIZE
The number of commands to remember in the command history (see
HISTORY below).

HISTFILE
The name of the file in which command history is saved. (See
HISTORY below.)

HISTFILESIZE
The maximum number of lines contained in the history file.
When this variable is assigned a value, the history file is
truncated, if necessary, to contain no more than that number
of lines.

OPTERR
If set to the value 1, bash displays error messages generated
by the getopts builtin command (see SHELL BUILTIN COMMANDS be-
low). OPTERR is initialized to 1 each time the shell is in-
voked or a shell script is executed.

PROMPT_COMMAND
If set, the value is executed as a command prior to issuing
each primary prompt.

IGNOREEOF

ignoreeof
Controls the action of the shell on receipt of an EOF charac-
ter as the sole input. If set, the value is the number of
consecutive EOF characters typed before bash exits. If the
variable exists but does not have a numeric value, or has no
value, the default value is 10. If it does not exist, EOF
signifies the end of input to the shell. This is only in ef-
fect for interactive shells.

HOSTTYPE
Automatically set to a string that uniquely describes the type
of machine on which bash is executing. The default is sys-
tem-dependent.

TMOUT
If set to a value greater than zero, the value is interpreted
as the number of seconds to wait for input after issuing the
primary prompt. Bash terminates after waiting for that number
of seconds if input does not arrive.

FCEDIT
The default editor for the fc builtin command.

FIGNORE
A colon-separated list of suffixes to ignore when performing
filename completion (see READLINE below). A filename whose
suffix matches one of the entries in FIGNORE is excluded from
the list of matched filenames. A sample value is ``.o:~''.

notify
If set, bash reports terminated background jobs immediately,
rather than waiting until before printing the next primary
prompt.

history_control
If set to a value of ignorespace, it means don't enter lines
which begin with a on the history list. If set to a
value of ignoredups, it means don't enter lines which match
the last entered line. If unset, or if set to any other value
than those above, all lines read by the parser are saved on
the history list.

command_oriented_history
If set, bash attempts to save all lines of a multiple-line
command in the same history entry. This allows easy re-edit-
ing of multi-line commands.

glob_dot_filenames
If set, bash includes filenames beginning with a `.' in the
results of pathname expansion.

allow_null_glob_expansion
If set, bash allows pathname patterns which match no files
(see Pathname Expansion below) to expand to a null string,
rather than themselves.

histchars
The two characters which control history expansion and tok-
enization. The first character is the history expansion char-
acter, that is, the character which signals the start of a
history expansion, normally `!'. The second character is the
character which signifies that the remainder of the line is a
comment, when found as the first character of a word.

nolinks
If set, the shell does not follow symbolic links when execut-
ing commands that change the current working directory. It
uses the physical directory structure instead. By default,
bash follows the logical chain of directories when performing
commands such as cd.

hostname_completion_file
Contains the name of a file in the same format as /etc/hosts
that should be read when the shell needs to complete a host-
name. You can change the file interactively; the next time
you want to complete a hostname bash adds the contents of the
new file to the already existing database.

noclobber
If set, bash does not overwrite an existing file with the >,
>&, and <> redirection operators. This variable may be over-
ridden when creating output files by using the redirection op-
erator >| instead of > (see also the -C option to the set
builtin command).

auto_resume
This variable controls how the shell interacts with the user
and job control. If this variable is set, single word simple
commands without redirections are treated as candidates for
resumption of an existing stopped job. There is no ambiguity
allowed; if there is more than one job beginning with the
string typed, the job most recently accessed is selected.

no_exit_on_failed_exec
If this variable exists, the shell does not exit if it cannot
execute the file specified in the exec command.

cdable_vars
If this is set, an argument to the cd builtin command that is
not a directory is assumed to be the name of a variable whose
value is the directory to change to.

pushd_silent
If set, the pushd and popd builtin commands do not print the
current directory stack after successful execution.

EXPANSION
Expansion is performed on the command line after it has been split
into words. There are seven kinds of expansion performed:
brace expansion, tilde expansion, parameter and variable expansion,
command substitution, arithmetic expansion, word splitting, and
pathname expansion.

The order of expansions is: brace expansion, tilde expansion, pa-
rameter, variable, command, and arithmetic substitution (done in a
left-to-right fashion), word splitting, and pathname expansion.

Only brace expansion, word splitting, and pathname expansion can
change the number of words of the expansion; other expansions ex-
pand a single word to a single word. The single exception to this
is the expansion of ``[email protected]'' as explained above (see PARAMETERS).

Brace Expansion

"Brace expansion" is a mechanism by which arbitrary strings may be
generated. This mechanism is similar to pathname expansion, but
the filenames generated need not exist. Patterns to be brace ex-
panded take the form of an optional preamble, followed by a series
of comma-separated strings between a pair of braces, followed by an
optional postamble. The preamble is prepended to each string con-
tained within the braces, and the postamble is then appended to
each resulting string, expanding left to right.

Brace expansions may be nested. The results of each expanded
string are not sorted; left to right order is preserved. For exam-
ple, a{d,c,b}e expands into `ade ace abe'.

Brace expansion is performed before any other expansions, and any
characters special to other expansions are preserved in the result.
It is strictly textual. Bash does not apply any syntactic inter-
pretation to the context of the expansion or the text between the
braces.

This construct is typically used as shorthand when the common pre-
fix of the strings to be generated is longer than in the above ex-
ample:

mkdir /usr/local/src/bash/{old,new,dist,bugs}
or
chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

Brace expansion introduces a slight incompatibility with tradi-
tional versions of sh, the Bourne shell. sh does not treat opening
or closing braces specially when they appear as part of a word, and
preserves them in the output. Bash removes braces from words as a
consequence of brace expansion. For example, a word entered to sh
as file{1,2} appears identically in the output. The same word is
output as file1 file2 after expansion by bash. If strict compati-
bility with sh is desired, start bash with the -nobraceexpansion
flag (see OPTIONS above) or disable brace expansion with the +o
braceexpand option to the set command (see SHELL BUILTIN COMMANDS
below).

Tilde Expansion

If a word begins with a tilde character (`~'), all of the charac-
ters preceding the first slash (or all characters, if there is no
slash) are treated as a possible login name. If this login name is
the null string, the tilde is replaced with the value of the param-
eter HOME. If HOME is unset, the home directory of the user exe-
cuting the shell is substituted instead.

If a `+' follows the tilde, the value of PWD is substituted. If a
`-' follows, the value of OLDPWD is used.

Each variable assignment is checked for unquoted instances of
tildes following a : or =. In these cases, tilde substitution is
also performed. Consequently, one may use pathnames with tildes in
PATH, MAILPATH, and CDPATH, and the shell will export the expanded
variables.

Parameter Expansion

The `$' character introduces parameter expansion, command substitu-
tion, or arithmetic expansion. The parameter name or symbol to be
expanded may be enclosed in braces, which are optional but serve to
protect the variable to be expanded from characters immediately
following it which could be interpreted as part of the name.


${parameter}
The value of parameter is substituted. The braces are re-
quired when parameter is a positional parameter with more than
one digit, or when parameter is followed by a character which
is not to be interpreted as part of its name.

In each of the cases below, word is subject to tilde expansion, pa-
rameter expansion, command substitution, and arithmetic expansion.
Bash tests for a parameter that is unset or null; omitting the
colon results in a test only for a parameter that is unset.


${parameter:-word}
Use Default Values. If parameter is unset or null, the expan-
sion of word is substituted. Otherwise, the value of parame-
ter is substituted.

${parameter:=word}
Assign Default Values. If parameter is unset or null, the ex-
pansion of word is assigned to parameter. The value of param-
eter is then substituted. Positional parameters and special
parameters may not be assigned to in this way.

${parameter:?word}
Display Error if Null or Unset. If parameter is null or un-
set, the expansion of word (or a message to that effect if
word is not present) is written to the standard error and the
shell, if it is not interactive, exits. Otherwise, the value
of parameter is substituted.

${parameter:+word}
Use Alternate Value. If parameter is null or unset, nothing
is substituted, otherwise the expansion of word is substi-
tuted.

${#parameter}
The length in characters of the value of parameter is substi-
tuted. If parameter is * or @, the length substituted is the
length of * expanded within double quotes.

${parameter#word}

${parameter##word}
The word is expanded to produce a pattern just as in pathname
expansion. If the pattern matches the beginning of the value
of parameter, then the expansion is the value of parameter
with the shortest matching pattern deleted (the ``#'' case) or
the longest matching pattern deleted (the ``##'' case).

${parameter%word}

${parameter%%word}
The word is expanded to produce a pattern just as in pathname
expansion. If the pattern matches a trailing portion of the
value of parameter, then the expansion is the value of parame-
ter with the shortest matching pattern deleted (the ``%''
case) or the longest matching pattern deleted (the ``%%''
case).

Command Substitution

Command substitution allows the output of a command to replace the
command name. There are two forms:


$(command)
or
`command`

Bash performs the expansion by executing command and replacing the
command substitution with the standard output of the command, with
any trailing newlines deleted.

When the old-style backquote form of substitution is used, back-
slash retains its literal meaning except when followed by $, `, or
. When using the $(command) form, all characters between the paren-
theses make up the command; none are treated specially.

Command substitutions may be nested. To nest when using the old
form, escape the inner backquotes with backslashes.

If the substitution appears within double quotes, word splitting
and pathname expansion are not performed on the results.

Arithmetic Expansion

Arithmetic expansion allows the evaluation of an arithmetic expres-
sion and the substitution of the result. The format for arithmetic
expansion is:

$[expression]

The expression is treated as if it were within double quotes, but a
double quote inside the braces is not treated specially. All to-
kens in the expression undergo parameter expansion, command substi-
tution, and quote removal. Arithmetic substitutions may be nested.

The evaluation is performed according to the rules listed below un-
der ARITHMETIC EVALUATION. If expression is invalid, bash prints a
message indicating failure and no substitution occurs.

Word Splitting

The shell scans the results of parameter expansion, command substi-
tution, and arithmetic expansion that did not occur within double
quotes for word splitting.

The shell treats each character of IFS as a delimiter, and splits
the results of the other expansions into words on these characters.
If the value of IFS is exactly , the default,
then any sequence of IFS characters serves to delimit words; other-
wise each occurrence of an IFS character is treated as a delimiter.
If the value of IFS is null, no word splitting occurs. IFS cannot
be unset.

Explicit null arguments ("" or '') are retained. Implicit null ar-
guments, resulting from the expansion of parameters that have no
values, are removed.

Note that if no expansion occurs, no splitting is performed.

Pathname Expansion

After word splitting, bash scans each word for the characters *, ?,
and [, unless the -f flag has been set. If one of these characters
appears, then the word is regarded as a pattern, and replaced with
an alphabetically sorted list of pathnames matching the pattern.
If no matching pathnames are found, and the shell variable al-
low_null_glob_expansion is unset, the word is left unchanged. If
the variable is set, the word is removed if no matches are found.
When a pattern is used for pathname generation, the character ``.''
at the start of a name or immediately following a slash must be
matched explicitly, unless the shell variable glob_dot_filenames is
set. The slash character must always be matched explicitly. In
other cases, the ``.'' character is not treated specially.

The special pattern characters have the following meanings:


* Matches any string, including the null string.

? Matches any single character.

[...]
Matches any one of the enclosed characters. A pair of charac-
ters separated by a minus sign denotes a range; any character
lexically between those two characters, inclusive, is matched.
If the first character following the [ is a ! or a ^ then any
character not enclosed is matched. A - or ] may be matched by
including it as the first or last character in the set.

Quote Removal

After the preceding expansions, all unquoted occurrences of the
characters , `, and " are removed.

REDIRECTION
Before a command is executed, its input and output may be redi-
rected using a special notation interpreted by the shell. Redirec-
tion may also be used to open and close files for the current shell
execution environment. The following redirection operators may ap-
pear anywhere in a simple command or may precede or follow a com-
mand. Redirections are processed in the order they appear, from
left to right.

In the following descriptions, if the file descriptor number is
omitted, and the first character of the redirection operator is <,
the redirection refers to the standard input (file descriptor 0).
If the first character of the redirection operator is >, the redi-
rection refers to the standard output (file descriptor 1).

The word that follows the redirection operator in the following de-
scriptions is subjected to brace expansion, tilde expansion, param-
eter expansion, command substitution, arithmetic expansion, quote
removal, and pathname expansion. If it expands to more than one
word, bash reports an error.

Redirecting Input

Redirection of input causes the file whose name results from the
expansion of word to be opened for reading on file descriptor n, or
the standard input (file descriptor 0) if n is not specified.

The general format for redirecting input is:

[n]
Redirecting Output

Redirection of output causes the file whose name results from the
expansion of word to be opened for writing on file descriptor n, or
the standard output (file descriptor 1) if n is not specified. If
the file does not exist it is created; if it does exist it is trun-
cated to zero size.

The general format for redirecting output is:

[n]>word

If the redirection operator is >bv, then the variable noclobber is
not consulted, and the file is created regardless of the value of
noclobber (see Shell Variables above).

Appending Redirected Output

Redirection of output in this fashion causes the file whose name
results from the expansion of word to be opened for appending on
file descriptor n, or the standard output (file descriptor 1) if n
is not specified. If the file does not exist it is created.

The general format for appending output is:

[n]>>word


Redirecting Standard Output and Standard Error

Bash allows both the standard output (file descriptor 1) and the
standard error output (file descriptor 2) to be redirected to the
file whose name is the expansion of word with this construct.

There are two formats for redirecting standard output and standard
error:

&>word
and
>&word

Of the two forms, the first is preferred. This is semantically
equivalent to

>word 2>&1

Here Documents

This type of redirection instructs the shell to read input from the
current source until a line containing only word (with no trailing
blanks) is seen. All of the lines read up to that point are then
used as the standard input for a command.

The format of here-documents is as follows:

<<[-]word
here-document
delimiter

No parameter expansion, command substitution, pathname expansion,
or arithmetic expansion is performed on word. If any characters in
word are quoted, the delimiter is the result of quote removal on
word, and the lines in the here-document are not expanded. Other-
wise, all lines of the here-document are subjected to parameter ex-
pansion, command substitution, and arithmetic expansion. In the
latter case, the pair is ignored, and must be used to
quote the characters , $, and `.

If the redirection operator is <<-, then all leading tab characters
are stripped from input lines and the line containing delimiter.
This allows here-documents within shell scripts to be indented in a
natural fashion.

"Duplicating File Descriptors"

The redirection operator

[n]<&word

is used to duplicate input file descriptors. If word expands to
one or more digits, the file descriptor denoted by n is made to be
a copy of that file descriptor. If word evaluates to -, file de-
scriptor n is closed. If n is not specified, the standard input
(file descriptor 0) is used.

The operator

[n]>&word

is used similarly to duplicate output file descriptors. If n is
not specified, the standard output (file descriptor 1) is used.

"Opening File Descriptors for Reading and Writing"

The redirection operator

[n]<>word

causes the file whose name is the expansion of word to be opened
for both reading and writing on file descriptor n, or as the stan-
dard input and standard output if n is not specified.

Note that the order of redirections is significant. For example,
the command

ls > dirlist 2>&1

directs both standard output and standard error to the file
dirlist, while the command

ls 2>&1 > dirlist

directs only the standard output to file dirlist, because the stan-
dard error was duplicated as standard output before the standard
output was redirected to dirlist.

FUNCTIONS
A shell function, defined as described above under SHELL GRAMMAR,
stores a series of commands for later execution. However, func-
tions are executed in the context of the current shell; no new pro-
cess is created to interpret them (contrast this with the execution
of a shell script). When a function is executed, the arguments to
the function become the positional parameters during its execution.
The special parameter # is updated to reflect the change. Posi-
tional parameter 0 is unchanged.

Variables local to the function may be declared with the local
builtin command. Ordinarily, variables and their values are shared
between the function and its caller.

If the builtin command return is executed in a function, the func-
tion completes and execution resumes with the next command after
the function call. When a function completes, the values of the
positional parameters and the special parameter # are restored to
the values they had prior to function execution.

Function names may be listed with the -f option to the declare or
typeset builtin commands. Functions may be exported so that sub-
shells automatically have them defined with the -f option to the
export builtin.

Functions may be recursive. No limit is imposed on the number of
recursive calls.

ALIASES
The shell maintains a list of aliases that may be set and unset
with the alias and unalias builtin commands. The first word of
each command is checked to see if it has an alias. If so, that
word is replaced by the text of the alias. The alias name and the
replacement text may contain any valid shell input, including the
metacharacters listed above. The first word of the replacement
text is tested for aliases, but a word that is identical to an
alias being expanded is not expanded a second time. This means
that one may alias ls to ls -F, for instance, and bash does not try
to recursively expand the replacement text. If the last character
of the alias value is a blank, then the next command word following
the alias is also checked for alias expansion.

Aliases are created and listed with the alias command, and removed
with the unalias command.

There is no mechanism for using arguments in the replacement text,
a la csh. If arguments are needed, a shell function should be
used.

The rules concerning the definition and use of aliases are somewhat
confusing. Bash always reads at least one complete line of input
before executing any of the commands on that line. Aliases are ex-
panded when a command is read, not when it is executed. Therefore,
an alias definition appearing on the same line as another command
does not take effect until the next line of input is read. This
means that the commands following the alias definition on that line
are not affected by the new alias. This behavior is also an issue
when functions are executed. Aliases are expanded when the func-
tion definition is read, not when the function is executed, because
a function definition is itself a compound command. As a conse-
quence, aliases defined in a function are not available until after
that function is executed. To be safe, always put alias defini-
tions on a separate line, and do not use alias in compound com-
mands.

Aliases are not expanded when the shell is not interactive.

Note that for almost every purpose, aliases are superseded by shell
functions.

"JOB CONTROL"
Job control refers to the ability to selectively stop (suspend) the
execution of processes and continue (resume) their execution at a
later point. A user typically employs this facility via an inter-
active interface supplied jointly by the system's terminal driver
and bash.

The shell associates a job with each pipeline. It keeps a table of
currently executing jobs, which may be listed with the jobs com-
mand. When bash starts a job asynchronously (in the background),
it prints a line that looks like:

[1] 25647

indicating that this job is job number 1 and that the process ID of
the single process in the job is 25647. Bash uses the job abstrac-
tion as the basis for job control.

To facilitate the implementation of the user interface to job con-
trol, the system maintains the notion of a current terminal process
group ID. Members of this process group (processes whose process
group ID is equal to the current terminal process group ID) receive
keyboard-generated signals such as SIGINT. These processes are
said to be in the foreground. Background processes are those whose
process group ID differs from the terminal's; such processes are
immune to keyboard-generated signals. Only foreground processes
are allowed to read from or write to the terminal. Background pro-
cesses which attempt to read from (write to) the terminal are sent
a SIGTTIN (SIGTTOU) signal by the terminal driver, which, unless
caught, causes the process to stop.

If the operating system on which bash is running supports job con-
trol, bash allows you to use it. Typing the suspend character
(typically ^Z, Control-Z) while a process is running causes that
process to be stopped and returns you to bash. Typing the "delayed
suspend" character (typically ^Y, Control-Y) causes the process to
be stopped when it attempts to read input from the terminal, and
control to be returned to bash. You may then manipulate the state
of this job, using the bg command to continue it in the background,
the fg command to continue it in the foreground, or the kill com-
mand to kill it. A ^Z takes effect immediately, and has the addi-
tional side effect of causing pending output and typeahead to be
discarded.

There are a number of ways to refer to a job in the shell. The
character % introduces a job name. Job number n may be referred to
as %n. A job may also be referred to using a prefix of the name
used to start it, or using a substring that appears in its command
line. For example, %ce refers to a stopped ce job. If a prefix
matches more than one job, bash reports an error. Using %?ce, on
the other hand, would refer to any job containing the string ce in
its command line. If the substring matches more than one job, bash
reports an error. The symbols %% and %+ refer to the shell's no-
tion of the current job, which is the last job stopped while it was
in the foreground. The "previous job" may be referenced using %-.
In output pertaining to jobs (e.g. the output of the jobs command),
the current job is always flagged with a +, and the previous job
with a -.

Simply naming a job can be used to bring it into the foreground:
%1 is a synonym for ``fg %1'', bringing job 1 from the background
into the foreground. Similarly, ``%1 &'' resumes job 1 in the
background, equivalent to ``bg %1''.

The shell learns immediately whenever a job changes state. Nor-
mally, bash waits until it is about to print a prompt before re-
porting changes in a job's status so as to not interrupt any other
output. If the variable notify is set, bash reports such changes
immediately. (See also the "-o notify" option to the set builtin
command.)

If you attempt to exit bash while jobs are stopped, the shell
prints a message warning you. You may then use the jobs command to
inspect their status. If you do this, or try to exit again immedi-
ately, you are not warned again, and the stopped jobs are termi-
nated.

SIGNALS
When bash is interactive, it ignores SIGTERM (so that kill 0 does
not kill an interactive shell), and SIGINT is caught and handled
(so that wait is interruptible). In all cases, bash ignores
SIGQUIT. If job control is in effect, bash ignores SIGTTIN, SIGT-
TOU, and SIGTSTP.

Synchronous jobs started by bash have signals set to the values in-
herited by the shell from its parent. Background jobs (jobs
started with &) ignore SIGINT and SIGQUIT. Commands run as a re-
sult of command substitution ignore the keyboard-generated job con-
trol signals SIGTTIN, SIGTTOU, and SIGTSTP.

"COMMAND EXECUTION"
After a command has been split into words, if it results in a sim-
ple command and an optional list of arguments, the following ac-
tions are taken.

If the command name contains no slashes, the shell attempts to lo-
cate it. If there exists a shell function by that name, that func-
tion is invoked as described above in FUNCTIONS. If the name does
not match a function, the shell searches for it in the list of
shell builtins. If a match is found, that builtin is invoked.

If the name is neither a shell function nor a builtin, and contains
no slashes, bash searches each element of the PATH for a directory
containing an executable file by that name. If the search is un-
successful, the shell prints an error message and returns a nonzero
exit status.

If the search is successful, or if the command name contains one or
more slashes, the shell executes the named program. Argument 0 is
set to the name given, and the remaining arguments to the command
are set to the arguments given, if any.

If this execution fails because the file is not in executable for-
mat, and the file is not a directory, it is assumed to be a shell
script, a file containing shell commands. A subshell is spawned to
execute it. This subshell reinitializes itself, so that the effect
is as if a new shell had been invoked to handle the script, with
the exception that the locations of commands remembered by the par-
ent (see hash below under SHELL BUILTIN COMMANDS) are retained by
the child.

If the program is a file beginning with #!, the remainder of the
first line specifies an interpreter for the program. The shell ex-
ecutes the specified interpreter on operating systems that do not
handle this executable format themselves. The arguments to the in-
terpreter consist of a single optional argument following the in-
terpreter name on the first line of the program, followed by the
name of the program, followed by the command arguments, if any.

ENVIRONMENT
When a program is invoked it is given an array of strings called
the environment. This is a list of name-value pairs, of the form
name=value.

The shell allows you to manipulate the environment in several ways.
On invocation, the shell scans its own environment and creates a
parameter for each name found, automatically marking it for export
to child processes. Executed commands inherit the environment.
The export and declare -x commands allow parameters and functions
to be added to and deleted from the environment. If the value of a
parameter in the environment is modified, the new value becomes
part of the environment, replacing the old. The environment inher-
ited by any executed command consists of the shell's initial envi-
ronment, whose values may be modified in the shell, less any pairs
removed by the unset command, plus any additions via the export and
declare -x commands.

The environment for any simple command or function may be augmented
temporarily by prefixing it with parameter assignments, as de-
scribed above in PARAMETERS. These assignment statements affect
only the environment seen by that command.

If the -k flag is set (see the set builtin command below), then all
parameter assignments are placed in the environment for a command,
not just those that precede the command name.

"EXIT STATUS"
For the purposes of the shell, a command which exits with a zero
exit status has succeeded. An exit status of zero indicates suc-
cess. A non-zero exit status indicates failure. When a command
terminates on a fatal signal, bash uses the value of 128+signal as
the exit status.

Bash itself returns the exit status of the last command executed,
unless a syntax error occurs, in which case it exits with a non-
zero value. See also the exit builtin command below.

PROMPTING
When executing interactively, bash displays the primary prompt PS1
when it is ready to read a command, and the secondary prompt PS2
when it needs more input to complete a command. Bash allows the
prompt to be customized by inserting a number of backslash-escaped
special characters that are decoded as follows:

t the time

d the date

n CRLF

s the name of the shell, the basename of $0 (the portion follow-
ing the final slash)

w the current working directory

W the basename of the current working directory

u the username of the current user

h the hostname

# the command number of this command

! the history number of this command

$ if the effective UID is 0, a #, otherwise a $

nnn character code in octal

a backslash

After the string is decoded, if the variable NO_PROMPT_VARS is not
set, it is expanded via parameter expansion, command substitution,
arithmetic expansion, and word splitting.

READLINE
This is the library that handles reading input when using an inter-
active shell, unless the -nolineediting option is given. By de-
fault, the line editing commands are similar to those of emacs. A
vi-style line editing interface is also available.

In this section, the emacs-style notation is used to denote
keystrokes. Control keys are denoted by C-key, e.g. C-n means Con-
trol-N. Similarly, meta keys are denoted by M-key, so M-x means
Meta-X. (On keyboards without a meta key, M-x means ESC x, i.e.
press the Escape key then the x key. The combination M-C-x means
ESC-Control-x, or press the Escape key then hold the Control key
while pressing the x key.)

The default key-bindings may be changed with an ~/.inputrc file.
Other programs that use this library may add their own commands and
bindings.

For example, placing

M-Control-u: universal-argument
or
C-Meta-u: universal-argument
into the ~/.inputrc would make M-C-u execute the command univer-
sal-argument.

The following symbolic character names are recognized: RUBOUT,
DEL, ESC, NEWLINE, SPACE, RETURN, LFD, TAB.

Placing

set editing-mode vi

into a ~/.inputrc file causes bash to start with a vi-like editing
mode. The editing mode may be switched during interactive use by
using the -o option to the set builtin command (see SHELL BUILTIN
COMMANDS below).

You can have readline use a single line for display, scrolling the
input between the two borders by placing

set horizontal-scroll-mode On

into a ~/.inputrc file.

The following is a list of the names of the commands and the de-
fault key-strokes to get them.

Commands for Moving


beginning-of-line (C-a)
Move to the start of the current line.

end-of-line (C-e)
Move to the end of the line.

forward-char (C-f)
Move forward a character.

backward-char (C-b)
Move back a character.

forward-word (M-f)
Move forward to the end of the next word.

backward-word (M-b)
Move back to the start of this, or the previous, word.

clear-screen (C-l)
Clear the screen leaving the current line at the top of the
screen.

Commands for Manipulating the History


accept-line (Newline, Return)
Accept the line regardless of where the cursor is. If this
line is non-empty, add it to the history list according to the
state of the history_control variable. If this line was a
history line, then restore the history line to its original
state.

previous-history (C-p)
Fetch the previous command from the history list, moving back
in the list.

next-history (C-n)
Fetch the next command from the history list, moving forward
in the list.

beginning-of-history (M-<)
Move to the first line in the history, the first line entered.

end-of-history (M->)
Move to the end of the input history, i.e., the line you are
entering.

reverse-search-history (C-r)
Search backward starting at the current line and moving `up'
through the history as necessary. This is an incremental
search.

forward-search-history (C-s)
Search forward starting at the current line and moving `down'
through the history as necessary.

shell-expand-line (M-C-e)
Expand the line the way the shell does when it reads it. This
performs alias and history expansion. See HISTORY below.

insert-last-argument (M-., M-_)
Insert the last argument to the previous command (the last
word on the previous line).

operate-and-get-next (C-O)
Accept the current line for execution and fetch the next line
relative to the current line from the history file for edit-
ing.

Commands for Changing Text


delete-char (C-d)
Delete the character under the cursor. If the cursor is at
the beginning of the line, and there are no characters in the
line, and the last character typed was not C-d, then return
EOF.

backward-delete-char (Rubout)
Delete the character behind the cursor. A numeric arg says to
kill the characters instead of deleting them.

quoted-insert (C-q, C-v)
Add the next character that you type to the line verbatim.
This is how to insert characters like C-q, for example.

tab-insert (M-TAB)
Insert a tab character.

self-insert (a, b, A, 1, !, ...)
Insert the character typed.

transpose-chars (C-t)
Drag the character before point forward over the character at
point. Point moves forward as well. If point is at the end
of the line, then transpose the two characters before point.
Negative arguments don't work.

transpose-words (M-t)
Drag the word behind the cursor past the word in front of the
cursor moving the cursor over that word as well.

upcase-word (M-u)
Uppercase the current (or following) word. With a negative
argument, do the previous word, but do not move point.

downcase-word (M-l)
Lowercase the current (or following) word. With a negative
argument, do the previous word, but do not move point.

capitalize-word (M-c)
Capitalize the current (or following) word. With a negative
argument, do the previous word, but do not move point.

Killing and Yanking


kill-line (C-k)
Kill the text from the current cursor position to the end of
the line. This saves the killed text on the kill-ring. (see
below)

backward-kill-line
Kill backward to the beginning of the line. This is normally
unbound, in favor of unix-line-discard, which emulates the be-
havior of the standard Unix terminal driver.

kill-word (M-d)
Kill from the cursor to the end of the current word, or if be-
tween words, to the end of the next word.

backward-kill-word (M-Rubout)
Kill the word behind the cursor.

unix-line-discard (C-u)
Do what C-u used to do in Unix line input. We save the killed
text on the kill-ring, though.

unix-word-rubout (C-w)
Do what C-w used to do in Unix line input. The killed text is
saved on the kill-ring. This is different than backward-
kill-word because the word boundaries differ.

yank (C-y)
Yank the top of the kill ring into the buffer at point.

yank-pop (M-y)
Rotate the kill-ring, and yank the new top. Only works fol-
lowing `yank' or `yank-pop'.

Arguments


digit-argument (M-0, M-1, ..., M--)
Add this digit to the argument already accumulating, or start
a new argument. M-- starts a negative argument.

universal-argument
Do what C-u does in emacs. By default, this is not bound to a
key.

Completing


complete (TAB)
Attempt to perform completion on the text before point. Bash
attempts completion treating the text as a variable (if the
text begins with $), username (if the text begins with ~),
hostname (if the text begins with @), or command (including
aliases and functions) in turn. If none of these produces a
match, filename completion is attempted.

possible-completions (M-?)
List the possible completions of the text before point.

complete-filename (M-/)
Attempt filename completion on the text before point.

possible-filename-completions (C-x /)
List the possible completions of the text before point, treat-
ing it as a filename.

complete-username (M-~)
Attempt completion on the text before point, treating it as a
username.

possible-username-completions (C-x ~)
List the possible completions of the text before point, treat-
ing it as a username.

complete-variable (M-$)
Attempt completion on the text before point, treating it as a
shell variable.

possible-variable-completions (C-x $)
List the possible completions of the text before point, treat-
ing it as a shell variable.

complete-hostname ([email protected])
Attempt completion on the text before point, treating it as a
hostname.

possible-hostname-completions (C-x @)
List the possible completions of the text before point, treat-
ing it as a hostname.

Miscellaneous


abort (C-g)
Abort the current editing command and ring the terminal's
bell.

do-uppercase-version (M-a, M-b, ...)
Run the command that is bound to the uppercased key.

prefix-meta (ESC)
Metafy the next character typed. This is for people without a
meta key. ESC f is equivalent to Meta-f.

undo (C-_)
Incremental undo, separately remembered for each line.

revert-line (M-r)
Undo all changes made to this line. This is like typing the
`undo' command enough times to get back to the beginning.

display-shell-version (C-x C-v)
Display version information about the current instance of
bash.

emacs-editing-mode (C-e)
When in vi editing mode, this causes a switch to emacs editing
mode.

vi-editing-mode (M-C-j or M-C-m)
When in emacs editing mode, this causes a switch to vi editing
mode.

HISTORY
The shell supports a history expansion feature that is similar to
the history expansion in csh. This section describes what syntax
features are available.

History expansion is performed immediately after a complete line is
read, before the shell breaks it into words. It takes place in two
parts. The first is determining which line from the previous his-
tory to use during substitution. The second is to select portions
of that line for inclusion into the current one. The line selected
from the previous history is the event, and the portions of that
line that are acted upon are words. The line is broken into words
in the same fashion as when reading input, so that several English,
or Unix, words surrounded by quotes are considered as one word.
Only backslash () can quote the history escape character, which is
! by default.

Event Designators

An event designator is a reference to a command line entry in the
history list.


! Start a history substitution, except when followed by a
, , , = or (.

!! Refer to the previous command. This is a synonym for `!-1'.

!n Refer to command line n.

!-n Refer to the current command line minus n.

!string
Refer to the most recent command starting with string.

!?string[?]
Refer to the most recent command containing string.

Word Designators

A : separates the event specification from the word designator. It
can be omitted if the word designator begins with a ^, $, *, or %.
Words are numbered from the beginning of the line, with the first
word being denoted by a 0 (zero).


# The entire command line typed so far. This means the current
command, not the previous command, so it really isn't a word
designator, and doesn't belong in this section.

0 (zero)
The zeroth word. For the shell, this is the command word.

n The nth word.

^ The first argument. That is, word 1.

$ The last argument.

% The word matched by the most recent `?string?' search.

x-y A range of words; `-y' abbreviates `0-y'.

* All of the words but the zeroth. This is a synonym for `1-$'.
It is not an error to use * if there is just one word in the
event; the empty string is returned in that case.

Modifiers

After the optional word designator, you can add a sequence of one
or more of the following modifiers, each preceded by a `:'.



h Remove a trailing pathname component, leaving only the head.

r Remove a trailing suffix of the form ".xxx", leaving the base-
name.

e Remove all but the suffix.

t Remove all leading pathname components, leaving the tail.

p Print the new command but do not execute it. This takes ef-
fect immediately, so it should be the last specifier on the
line.

"ARITHMETIC EVALUATION"
The shell allows arithmetic expressions to be evaluated, under cer-
tain circumstances (see the let builtin command and Arithmetic Ex-
pansion). Evaluation is done in long integers with no check for
overflow, though division by 0 is trapped and flagged as an error.
The following list of operators is grouped into levels of equal-
precedence operators. The levels are listed in order of decreasing
precedence.


- unary minus

! logical NOT

* / %
multiplication, division, remainder

+ - addition, subtraction

<= >= < >
comparison

== !=
equality and inequality

= assignment

Shell variables are allowed as operands; parameter expansion is
performed before the expression is evaluated. The value of a pa-
rameter is coerced to a long integer within an expression. A shell
variable need not have its integer attribute turned on to be used
in an expression.

Operators are evaluated in order of precedence. Sub-expressions in
parentheses are evaluated first and may override the precedence
rules above.

"SHELL BUILTIN COMMANDS"

: [arguments]
No effect; the command does nothing beyond expanding arguments
and performing any specified redirections. A zero exit code
is returned.

. filename

source filename
Read and execute commands from filename in the current shell
environment and return the exit status of the last command ex-
ecuted from filename. Pathnames in PATH are used to find the
directory containing filename, if filename does not contain a
slash. The file searched for in PATH need not be executable.
The current directory is searched if no file is found in PATH.
The return status is the status of the last command exited
within the script (true if no commands are executed), and
false if filename is not found.

alias [name[=value] ...]
Alias with no arguments prints the list of aliases in the form
name=value on standard output. When arguments are supplied,
an alias is defined for each name whose value is given. A
trailing space in value causes the next word to be checked for
alias substitution when the alias is expanded. Alias returns
true unless a name is given for which no alias has been de-
fined.

bg [jobspec]
Place jobspec in the background, as if it had been started
with &. If jobspec is not present, the shell's notion of the
current job is used.

bind [-lvd] [-q name]

bind -f filename

bind keyseq:function-name
Display current readline key and function bindings, or bind a
key sequence to a readline function or macro. The binding
syntax accepted is identical to that of .inputrc, but each
binding must be passed as a separate argument; e.g. '"C-xC-r":
re-read-init-file'. Options, if supplied, have the following
meanings:

-l List the names of all readline functions

-v List current function names and bindings

-d Dump function names and bindings in such a way that they can
be re-read

-f filename
Read key bindings from filename

-q function
Query about which keys invoke the named function

break [n]
Exit from within a for, while, or until loop. If n is speci-
fied, break n levels. n must be >= 1. If n is greater than
the number of enclosing loops, all enclosing loops are exited.
The return value is 0 unless the shell is not executing a loop
when break is executed.

builtin [shell-builtin [arguments]]
Execute the specified shell builtin, passing it arguments, and
return its exit status. This is useful when you wish to de-
fine a function whose name is the same as a shell builtin, but
need the functionality of the builtin within the function it-
self. The cd builtin is commonly redefined this way.

cd [dir]
Change the current directory to dir. The variable HOME is the
default dir. The variable CDPATH defines the search path for
the directory containing dir. Alternative directory names are
separated by a colon (:). A null directory name in CDPATH is
the same as the current directory, i.e. ``.''. If dir begins
with a slash (/), then CDPATH is not used. An argument of -
is equivalent to $OLDPWD. The return value is true if the di-
rectory was successfully changed; false otherwise.

command [-p] [command [arg ...]]
Run command with args suppressing the normal shell function
lookup. Only builtin commands or commands found in the PATH
are executed. If the -p option is given, the search for com-
mand is performed using a default value for PATH that is guar-
anteed to find all of the standard utilities. An argument of
-- disables option checking for the rest of the arguments. If
an error occurred or command cannot be found, the exit status
is 127. Otherwise, the exit status of the command builtin is
the exit status of command.

continue [n]
Resume the next iteration of the enclosing for, while, or un-
til loop. If n is specified, resume at the nth enclosing
loop. n must be >= 1. If n is greater than the number of en-
closing loops, the last enclosing loop (the `top-level' loop)
is resumed. The return value is 0 unless the shell is not ex-
ecuting a loop when continue is executed.

declare
[-frxi] [name[=value]]

typeset [-frxi] [name[=value]]
Declare variables and/or give them attributes. If no names
are given, then display the values of variables instead.

-f Use function names only

-r Make names readonly. These names cannot then be assigned val-
ues by subsequent assignment statements.

-x Mark names for export to subsequent commands via the environ-
ment.

-i The variable is treated as an integer; arithmetic evaluation
(see "ARITHMETIC EVALUATION" ") " is performed when the vari-
able is assigned a value.

Using `+' instead of `-' turns off the attribute instead. When
used in a function, makes names local, as with the local command.

dirs [-l]
Display the list of currently remembered directories. Direc-
tories are added to the list with the pushd command; the popd
command moves back up through the list. The -l option pro-
duces a longer listing; the default listing format uses a
tilde to denote the home directory.

echo [-ne] [arg ...]
Output the args, separated by spaces. If -n is specified, the
trailing newline is suppressed. If the -e option is given,
interpretation of the following backslash-escaped characters
is enabled:

a alert (bell)

b backspace

c suppress trailing newline

f form feed

n new line

r carriage return

t horizontal tab

v vertical tab

backslash

nnn the character whose ASCII code is nnn (octal)

enable [-n] [name ...]
Enable and disable builtin shell commands. This allows the
execution of a disk command which has the same name as a shell
builtin without specifying a full pathname. If -n is used,
each name is disabled; otherwise, names are enabled. For ex-
ample, to use the test found in PATH instead of the shell
builtin version, type ``enable -n test''.

eval [arg ...]
The args are read and concatenated together into a single com-
mand. This command is then read and executed by the shell,
and its exit status is returned as the value of the eval com-
mand. If there are no args, or only null arguments, eval re-
turns true.

exec [[-] command [arguments]]
If command is specified, it replaces the shell. No new pro-
cess is created. The arguments become the arguments to com-
mand. If the first argument is -, the shell places a dash in
the zeroth arg passed to command. This is what login does.
If the file cannot be executed for some reason, the shell ex-
its, unless the shell variable no_exit_on_failed_exec exists.
If command is not specified, any redirections take effect in
the current shell.

exit [n]

bye [n]
Cause the shell to exit with a status of n. If n is omitted,
the exit status is that of the last command executed. A trap
on EXIT is executed before the shell terminates.

export [-npf] [name[=word]] ...
The supplied names are marked for automatic export to the en-
vironment of subsequently executed commands. If the -f option
is given, the names refer to functions. If no names are
given, or if the -p option is supplied, a list of all names
that are exported in this shell is printed. The -n option
causes the export property to be removed from the named vari-
ables. An argument of -- disables option checking for the
rest of the arguments. export returns an exit status of true
unless an illegal option is encountered.

fc [-e ename] [-nlr] [first] [last]

fc -s [pat=rep] [cmd]
Fix Command. In the first form, a range of commands from
first to last is selected from the history list. First and
last may be specified as a string (to locate the last command
beginning with that string) or as a number (an index into the
history list, where a negative number is used as an offset
from the current command number). If last is not specified it
is set to the current command for listing (so that fc -l -10
prints the last 10 commands) and to first otherwise. If first
is not specified it is set to the previous command for editing
and -16 for listing.

The -n flag suppresses the command numbers when listing. The
-r flag reverses the order of the commands. If the -l flag is
given, the commands are listed on standard output. Otherwise,
the editor given by ename is invoked on a file containing
those commands. If ename is not given, the value of the
FCEDIT variable is used, and the value of EDITOR if FCEDIT is
not set. If neither variable is set, vi is used. When edit-
ing is complete, the edited commands are echoed and executed.

In the second form, the command is re-executed after the sub-
stitution old=new is performed. A useful alias to use with
this is ``r=fc -s'', so that typing ``r cc'' runs the last
command beginning with ``cc'' and typing ``r'' re-executes the
last command.

fg [jobspec]
Place jobspec in the foreground, and make it the current job.
If jobspec is not present, the shell's notion of the current
job is used.

getopts optstring name [args]
getopts is used by shell procedures to parse positional param-
eters. optstring contains the option letters to be recog-
nized; if a letter is followed by a colon, the option is ex-
pected to have an argument, which should be separated from it
by white space. Each time it is invoked, getopts places the
next option in the shell variable name, initializing name if
it does not exist, and the index of the next argument to be
processed into the variable OPTIND. OPTIND is initialized to
1 each time the shell or a shell script is invoked. When an
option requires an argument, getopts places that argument into
the variable OPTARG. The shell does not reset OPTIND automat-
ically; it must be manually reset between multiple calls to
getopts within the same shell invocation if a new set of pa-
rameters is to be used.

getopts can report errors in two ways. If the first character
of optstring is a colon, silent error reporting is used. In
normal operation diagnostic messages are printed when illegal
options or missing option arguments are encountered. If the
variable OPTERR is set to 0, no error message will be dis-
played, even if the first character of optstring is not a
colon.

If an illegal option is seen, getopts places ? into name and,
if not silent, prints an error message and unsets OPTARG. If
getopts is silent, the option character found is placed in OP-
TARG and no diagnostic message is printed.

If a required argument is not found, and getopts is not
silent, a question mark (?) is placed in name, OPTARG is un-
set, and a diagnostic message is printed. If getopts is
silent, then a colon (:) is placed in name and OPTARG is set
to the option character found.

getopts normally parses the positional parameters, but if more
arguments are given in args, getopts parses those instead.
getopts returns true if an option, specified or unspecified,
is found. It returns false if the end of options is encoun-
tered or an error occurs.

hash [-r] [name]
For each name, the full pathname of the command is determined
and remembered. The -r option causes the shell to forget all
remembered locations. If no arguments are given, information
about remembered commands is printed. An argument of -- dis-
ables option checking for the rest of the arguments. The re-
turn status is true unless a name is not found or an illegal
option is supplied.

help [pattern]
Display helpful information about builtin commands. If pat-
tern is specified, help gives detailed help on all commands
matching pattern; otherwise a list of the builtins is printed.

history
[n]

history -rwan [filename]
With no options, display the command history list with line
numbers. Lines listed with with a * have been modified. An
argument of n lists only the last n lines. If a non-option
argument is supplied, it is used as the name of the history
file; if not, the value of HISTFILE (default ~/.bash_history)
is used. Options, if supplied, have the following meanings:

-a Append the ``new'' history lines (history lines entered since
the beginning of the current bash session) to the history file

-n Read the history lines not already read from the history file
into the current history list. These are lines appended to
the history file since the beginning of the current bash ses-
sion.

-r read the contents of the history file and use them as the cur-
rent history

-w write the current history to the history file, overwriting the
history file's contents.

jobs [-lnp] [ jobspec ... ]

jobs -x command [ args ... ]
The first form lists the active jobs. The -l option lists
process IDs in addition to the normal information; the -p op-
tion lists only the process ID of the job's process group
leader. The -n option displays only jobs that have changed
status since last notfied. If jobspec is given, output is re-
stricted to information about that job.

If the -x option is supplied, jobs replaces any jobspec found
in command or args with the corresponding process group ID,
and executes command passing it args.

kill [-s sigspec | -sigspec] [pid | jobspec] ...

kill -l [signum]
Send the signal named by sigspec to the processes named by pid
or jobspec. sigspec is either a signal name such as SIGKILL
or a signal number. If sigspec is a signal name, the name is
case insensitive and may be given with or without the SIG pre-
fix. If sigspec is not present, then SIGTERM is assumed. An
argument of -l lists the signal names. If any arguments are
supplied when -l is given, the names of the specified signals
are listed. An argument of -- disables option checking for
the rest of the arguments. kill returns true if at least one
signal was successfully sent, or false if an error occurs.

let arg [arg ...]
Each arg is an arithmetic expression to be evaluated (see
ARITHMETIC EVALUATION). If the last arg evaluates to 0, let
returns 1; 0 is returned otherwise.

local [name[=value]]
Create a local variable named name, and assign it value. When
local is used within a function, it causes the variable name
to have a visible scope restricted to that function and its
children. With no operands, local writes a list of local
variables to the standard output. It is an error to use local
when not within a function.

logout
Exit a login shell.

popd [+/-n]
Removes entries from the directory stack. With no arguments,
removes the top directory from the stack, and performs a cd to
the new top directory.

+n removes the nth entry counting from the left of the list shown
by dirs, starting with zero. For example: ``popd +0'' re-
moves the first directory, ``popd +1'' the second.

-n removes the nth entry counting from the right of the list
shown by dirs, starting with zero. For example: ``popd -0''
removes the last directory, ``popd -1'' the next to last.

If the variable pushd_silent is unset and the popd command is suc-
cessful, a dirs is performed as well.

pushd
dir

pushd +/-n
Adds a directory to the top of the directory stack, or rotates
the stack, making the new top of the stack the current working
directory. With no arguments, exchanges the top two directo-
ries.

+n Rotates the stack so that the nth directory (counting from the
left of the list shown by dirs) is at the top.

-n Rotates the stack so that the nth directory (counting from the
right) is at the top.

dir adds dir to the directory stack at the top, making it the new
current working directory.

If the variable pushd_silent is not set and the pushd command is
successful, a dirs is performed as well.

pwd Print the absolute pathname of the current working directory.
The path printed contains no symbolic links (but see the de-
scription of nolinks under Shell Variables above).

read [-r] [name ...]
One line is read from the standard input, and the first word
is assigned to the first name, the second word to the second
name, and so on, with leftover words assigned to the last
name. Only the characters in IFS are recognized as word de-
limiters. The return code is zero, unless end-of-file is en-
countered. If the -r option is given, a backslash-newline
pair is not ignored, and the backslash is considered to be
part of the line.

readonly [-pf] [name ...]
The given names are marked readonly and the values of these
names may not be changed by subsequent assignment. If the -f
option is supplied, the functions corresponding to the names
are so marked. If no arguments are given, or if the -p option
is supplied, a list of all readonly names is printed. An ar-
gument of -- disables option checking for the rest of the ar-
guments.

return [n]
Causes a function to exit with the return value specified by
n. If n is omitted, the return status is that of the last com-
mand executed in the function body. If used outside a func-
tion, but during execution of a script by the . (source) com-
mand, it causes the shell to stop executing that script and
return either n or the exit status of the last command exe-
cuted within the script as the exit status of the script.

set [-aefhknotuvxldCH] [arg ...]

-a Automatically mark variables which are modified or created
for export to the environment of subsequent commands.

-e Exit immediately if a simple-command (see SHELL GRAMMAR
above) exits with a non-zero status. The shell does not
exit if the command that fails is part of an until or while
loop, part of an if statement, part of a && or bvbv list,
or if the command's return value is being inverted via !.

-f Disable pathname expansion.

-h Locate and remember function commands as functions are de-
fined. Function commands are normally looked up when the
function is executed.

-k All keyword arguments are placed in the environment for a
command, not just those that precede the command name.

-m Monitor mode. Job control is enabled. This flag is on by
default for interactive shells on systems that support it
(see JOB CONTROL above). Background processes run in a
separate process group and a line containing their exit
status is printed upon their completion.

-n Read commands but do not execute them. This may be used to
check a shell script for syntax errors. This is ignored
for interactive shells.

-o option-name
The option-name can be one of the following:

allexport
Same as -a.

braceexpand
The shell performs curly brace expansion (see Brace Expan-
sion above). This is on by default.

emacs Use an emacs-style command line editing interface.

errexit Same as -e.

histexpand
Same as -H.

ignoreeof
The effect is as if the shell command `IGNOREEOF=10' had
been executed (see Shell Variables above).

monitor Same as -m.

noclobber
Same as -C.

noexec Same as -n.

noglob Same as -f.

nohash Same as -d.

notify The effect is as if the shell command `notify=' had been
executed (see Shell Variables above).

nounset Same as -u.

verbose Same as -v.

vi Use a vi-style command line editing interface.

xtrace Same as -x.

If no option-name is supplied, the values of the current options
are printed.

-t Exit after reading and executing one command.

-u Treat unset variables as an error when performing parameter
expansion. If expansion is attempted on an unset variable,
the shell prints an error message, and, if not interactive,
exits with a non-zero status.

-v Print shell input lines as they are read.

-x After expanding each simple-command, bash displays the ex-
panded value of PS4, followed by the command and its ex-
panded arguments.

-l Save and restore the binding of name in a for name [in
word] command (see SHELL GRAMMAR above).

-d Disable the hashing of commands that are looked up for exe-
cution. Normally, commands are remembered in a hash table,
and once found, do not have to be looked up again.

-C The effect is as if the shell command `noclobber=' had been
executed (see Shell Variables above).

-H Enable ! style history substitution. This flag is on by by
default.

-- If no arguments follow this flag, then the positional pa-
rameters are unset. Otherwise, the positional parameters
are set to the args, even if some of them begin with a -.

- Signal the end of options, cause all remaining args to be
assigned to the positional parameters. The -x and -v op-
tions are turned off. If there are no args, the positional
parameters remain unchanged.

Using + rather than - causes these flags to be turned off. The
flags can also be specified as options to an invocation of the
shell. The current set of flags may be found in $-. After the op-
tion arguments are processed, the remaining args are treated as
values for the positional parameters and are assigned, in order, to
$1, $2, ... $9. If no options or args are supplied, all shell
variables are printed. The return status is always true unless an
illegal option is encountered.

shift [n]
The positional parameters from n+1 ... are renamed to $1 ....
If n is not given, it is assumed to be 1. The exit status is 1
if n is greater than $#; otherwise 0.

suspend [-f]
Suspend the execution of this shell until it receives a SIG-
CONT signal. The -f option says not to complain if this is a
login shell; just suspend anyway.

test expr

[ expr ]
Return a status of 0 (true) or 1 (false) depending on the
evaluation of the conditional expression expr. Expressions
may be unary or binary. Unary expressions are often used to
examine the status of a file. There are string operators and
numeric comparison operators as well.

-b file
True if file exists and is block special.

-c file
True if file exists and is character special.

-d file
True if file exists and is a directory.

-e file
True if file exists

-f file
True if file exists and is a regular file.

-g file
True if file exists and is set-group-id.

-k file
True if file has its ``sticky'' bit set.

-L file
True if file exists and is a symbolic link.

-p file
True if file exists and is a named pipe.

-r file
True if file exists and is readable.

-s file
True if file exists and has a size greater than zero.

-S file
True if file exists and is a socket.

-t [fd]
True if fd is opened on a terminal. If fd is omitted, it de-
faults to 1 (standard output).

-u file
True if file exists and its set-user-id bit is set.

-w file
True if file exists and is writable.

-x file
True if file exists and is executable.

-O file
True if file exists and is owned by the effective user id.

-G file
True if file exists and is owned by the effective group id.

file1 -nt file2
True if file1 is newer (according to modification date) than
file2.

file1 -ot file2
True if file1 is older than file2.

file1 -ef file
True if file1 and file2 have the same device and inode num-
bers.

-z string
True if the length of string is zero.

-n string

string
True if the length of string is non-zero.

string1 = string2
True if the strings are equal.

string1 != string2
True if the strings are not equal.

! expr
True if expr is false.

expr1 -a expr2
True if both expr1 AND expr2 are true.

expr1 -o expr2
True if either expr1 OR expr2 is true.

arg1 OP arg2
OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arith-
metic binary operators return true if arg1 is equal, not-
equal, less-than, less-than-or-equal, greater-than, or
greater-than-or-equal than arg2, respectively. Arg1 and arg2
may be positive integers, negative integers, or the special
expression -l string, which evaluates to the length of string.

times
Print the accumulated user and system times for the shell and
for processes run from the shell.

trap [arg] [sigspec]
The command arg is to be read and executed when the shell re-
ceives signal(s) sigspec. If arg is absent or -, all speci-
fied signals are are reset to their original values (the val-
ues they had upon entrance to the shell). If arg is the null
string this signal is ignored by the shell and by the commands
it invokes. sigspec is either a signal name in , or
a signal number. If sigspec is EXIT (0) the command arg is
executed on exit from the shell. With no arguments, trap
prints the list of commands associated with each signal num-
ber. The -l option causes the shell to print a list of signal
names and their corresponding numbers. An argument of -- dis-
ables option checking for the rest of the arguments. Signals
ignored upon entry to the shell cannot be trapped or reset.
Trapped signals are reset to their original values in a child
process when it is created. The return status is false if ei-
ther then trap name or number is invalid; otherwise trap re-
turns true.

type [-all] [-type | -path] [name ...]
With no options, indicate how each name would be interpreted
if used as a command name. If the -type flag is used, type
prints a phrase which is one of alias, keyword, function,
builtin, or file if name is an alias, shell reserved word,
function, builtin, or disk file, respectively. If the name is
not found, then nothing is printed, and an exit status of
false is returned. If the -path flag is used, type either re-
turns the name of the disk file that would be executed if name
were specified as a command name, or nothing if -type would
not return file. If a command is hashed, -path prints the
hashed value, not necessarily the file that appears first in
PATH. If the -all flag is used, type prints all of the places
that contain an executable named name. This includes aliases
and functions, if and only if the -path flag is not also used.
The table of hashed commands is not consulted when using -all.
type accepts -a, -t, and -p in place of -all, -type, and
-path, respectively. An argument of -- disables option check-
ing for the rest of the arguments. type returns true if any
of the arguments are found, false if none are found.

ulimit [-SHacdfmstpn [limit]]
Ulimit provides control over the resources available to the
shell and to processes started by it, on systems that allow
such control. The value of limit can be a number in the unit
specified for the resource, or the value unlimited. The H and
S options specify that the hard or soft limit is set for the
given resource. A hard limit cannot be increased once it is
set; a soft limit may be increased up to the value of the hard
limit. If neither H nor S is specified, the command applies
to the soft limit. If limit is omitted, the current value of
the soft limit of the resource is printed, unless the H option
is given. When more than one resource is specified, the limit
name and unit is printed before the value. Other options are
interpreted as follows:

-a all current limits are reported

-c the maximum size of core files created

-d the maximum size of a process's data segment

-f the maximum size of files created by the shell

-m the maximum resident set size

-s the maximum stack size

-t the maximum amount of cpu time in seconds

-p the pipe size in 512-byte blocks (this may not be set)

-n the maximum number of open file descriptors (most systems do
not allow this value to be set, only displayed)

An argument of -- disables option checking for the rest of the ar-
guments. If limit is given, it is the new value of the specified
resource (the -a option is display only). If no option is given,
then -f is assumed. Values are in 1024-byte increments, except for
-t, which is in seconds, and -p, which is in units of 512-byte
blocks.

umask [-S] [mode]
The user file-creation mask is set to mode. If mode begins
with a digit, it is interpreted as an octal number; otherwise
it is interpreted as a symbolic mode mask similar to that ac-
cepted by chmod(1). If mode is omitted, or if the -S option
is supplied, the current value of the mask is printed. The -S
option causes the mask to be printed in symbolic form; the de-
fault output is an octal number. An argument of -- disables
option checking for the rest of the arguments.

unalias [name ...]
Remove names from the list of defined aliases. The return
value is true unless name is not a defined alias.

unset [-fv] [name ...]
For each name, remove the corresponding variable or, given the
-f option, function. An argument of -- disables option check-
ing for the rest of the arguments. Note that PATH, IFS, PPID,
PS1, PS2, UID, and EUID cannot be unset. If any of RANDOM,
SECONDS, or LINENO are unset, they lose their special proper-
ties, even if they are subsequently reset. The exit status is
true unless the variable name does not exist or is non-unset-
table.

wait [n]
Wait for the specified process and report its termination sta-
tus. n may be a process ID or a job specification; if a job
spec is given, all processes in that job's pipeline are waited
for. If n is not given, all currently active child processes
are waited for, and the return code is zero.

INVOCATION
A login shell is one whose first character of argument zero is a -
, or one started with the -login flag.

An interactive shell is one whose standard input and output are
both connected to terminals (as determined by isatty(3)), or one
started with the -i flag. PS1 is set and $- includes i if bash is
interactive, allowing a way to test this state from a shell script
or a startup file.

Login shells:
On login:
if /etc/profile exists, source it.

if ~/.bash_profile exists, source it,
else if ~/.bash_login exists, source it,
else if ~/.profile exists, source it.

On logout:
if ~/.bash_logout exists, source it.

Non-login interactive shells:
On startup:
if ~/.bashrc exists, source it.

Non-interactive shells:
On startup:
if the environment variable ENV is non-null, expand
it and source the file it names.


"SEE ALSO"

The Gnu Readline Library, Brian Fox

The Gnu History Library, Brian Fox

A System V Compatible Implementation of 4.2BSD Job Control, David
Lennert

How to wear weird pants for fun and profit, Brian Fox

sh(1), ksh(1), csh(1)

FILES

/bin/bash
The bash executable

/etc/profile
The systemwide initialization file, executed for login shells

~/.bash_profile
The personal initialization file, executed for login shells

~/.bashrc
The individual per-interactive-shell startup file

~/.inputrc
Individual Readline initialization file

AUTHORS
Brian Fox, Free Software Foundation (primary author)
[email protected]

Chet Ramey, Case Western Reserve University
[email protected]

BUG REPORTS
If you find a bug in bash, you should report it. But first, you
should make sure that it really is a bug, and that it appears in
the latest version of bash that you have.

Once you have determined that a bug actually exists, mail a bug re-
port to [email protected] If you have a fix, you are
welcome to mail that as well! Suggestions and `philosophical' bug
reports may be mailed to [email protected] or posted to the
Usenet newsgroup gnu.bash.bug.

ALL bug reports should include:


The version number of bash

The hardware and operating system

The compiler used to compile

A description of the bug behaviour

A short script or `recipe' which exercises the bug

Comments and bug reports concerning this manual page should be di-
rected to [email protected]

BUGS

It's too big and too slow.

There are some subtle differences between bash and traditional ver-
sions of sh, mostly because of the POSIX specification.

Aliases are confusing in some uses.


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