Brik 1.0
A free CRC-32 program
by
Rahul Dhesi

Brik 1.0 generates and verifies 32-bit CRC values (checksums). It is
designed to generate CRCs for text files that are the same on all computer
systems that use the ASCII character set, provided each text file is in the
usual text file format for each system. Brik 1.0 will also optionally use
binary CRCs calculated using every byte in a file. Such binary CRCs are
portable across systems for binary files that are moved from system to system
without any newline conversion.

The general usage format is:

brik -gcGCbfvsWT [file] ...

The brackets mean that "file", which is the name of a file, is optional. The
three dots indicate that more than one filenames may be typed (separated by
blanks). Exactly one of the options -c, -C, -g, -G, or -h is required. The
-h option gives a help screen.

In addition to -h, the brik options available (as they appear on the help
screen) are:

-g look for Checksum: header, generate CRC for rest of file
-c get CRC from header, verify CRC of rest of file
-G generate CRC for entire file (add -b for binary files)
-C verify all file CRCs from output of -G (-f is not needed)
-b use binary mode--read file byte by byte, not line by line
-f read filenames (wildcards ok) from specified files
-v be verbose, report all results (else only errors are reported)
-s be silent, say nothing, just return status code
-W after generating CRC with -g, write it to original header
-T include trailing empty lines, normally ignored (text mode only)


VERIFYING CRC HEADERS

The primary intended use of brik is to verify Checksum: headers in Usenet
postings and in C and Pascal source files. A Checksum: header looks like
this:

Checksum: 9485762645 (verify or update this with "brik")

The word "Checksum:" must occur at the beginning of a line. It is followed
by a colon, an optional blank, a ten-digit CRC-32 value, and any arbitrary
optional string such as the comment shown above. When brik is invoked with
the syntax

brik -c file ...

it will search for the Checksum: header in each specified file, read the CRC
value from that header, calculate the CRC-32 for all lines in the file that
occur *after* the header line, and report an error if the two values do not
match. Brik ignores any trailing empty lines.


CALCULATING CRC HEADERS

The command

brik -g file ...

tells brik to look for the Checksum: header in each specified file, calculate
the CRC of the lines in the file following the header, and print the CRC and
filename without changing the file in any way. You can also ask brik to
update the Checksum: header with the following command:

brik -gW file ...

This causes brik to fill in the newly-calculated CRC in the Checksum: header.
If there is not enough space for the CRC value in the existing header, brik
reports an error and does not change the existing header. To initially add
a Checksum: header to a file, insert a line of the following form into the
file with a text editor:

Checksum: XXXXXXXXXX -- this is an optional comment

The word "Checksum" must be at the beginning of a line. The ten 'X'
characters shown can be any ten characters. They will be later replaced by
the calculated CRC value. They do not need to be 'X'. The comment
following them is optional and can be any arbitrary string of characters
after the CRC field, separated from it by a blank. As an example, in a C
source file called "main.c", you might have:

/*
Checksum: XXXXXXXXXX (verify or update this with brik)
*/

Once a header like this exists in the file, invoke brik as follows:

brik -gW main.c

This will cause the ten 'X' characters to be replaced with the calculated
checksum, giving something like this:

/*
Checksum: 1922837484 (verify or update this with brik)
*/

Later you can use the command

brik -c main.c

to verify that the contents of the file following the header have the same
CRC as the stored value.

If brik is invoked with the -c or -g options and it cannot find a Checksum:
header in a file, it prints a row of question marks. If it is invoked with
the -gW option and it does not find enough character positions after the
"Checksum:" string to hold the CRC, it does not fill in the CRC and prints an
error message.

When calculating the CRC to fill in with the -gW option, brik ignores any
trailing empty lines in the file.


WHOLE-FILE CRCS

A "whole-file" CRC calculation is done for the entire contents of a file,
without looking for a Checksum: header. The command

brik -G file ...

asks brik to do this calculation for all specified files. The output from
this command is a list of files and their whole-file CRCs. It is sent to the
standard output stream, which in most cases is your screen. The output
should be saved in a file by redirecting it. For example, the command
"brik -G *.h *.c > crc.lst" on an MS-DOS system might yield the following in
the output file "crc.lst":

# Whole file CRCs generated by Brik v1.0. Use "brik -C" to verify them.

# CRC-32 filename
# ------ --------

2566277976 getopt.c
100594287 brik.c
1151475469 vms.c
3929503738 turboc.c
2424271922 addbfcrc.c
1943472856 assert.h
2601923477 brik.h

The output of the -G option is in free format. The output file may be edited
by hand. Empty lines and lines beginning with '#' will be ignored by brik
when it is later asked to read this file.

This list of filenames and whole-file CRCs may be verified by a command like
this:

brik -C crc.lst

This makes brik read the file "crc.lst", get the CRCs and filenames from it,
do the CRC calculation again for each file, and report an error if it does
not match the CRC recorded inside "crc.lst".

**IX and MS-DOS users (and others who can pipe the output of one command into
another) could use a command like the following to see if brik's -G and -C
options are working:

brik -G file ... | brik -C

This invokes "brik -G" on some files, sending the output to a pipe where it
becomes the input of "brik -C". If no filename is specified, brik reads from
standard input, so "brik -C" will read from the pipe and concurrently verify
all the CRCs that are being generated by "brik -G".

Whole-file CRCs are normally generated in text mode, in which a file is
treated as lines of text. In this mode brik ignores any trailing empty lines
in a file. You can also generate whole-file CRCs in binary mode. See
below.


BINARY VERSUS TEXT MODE

Brik can work in two different modes. The most common mode, used by the -g,
-c, and -G options, is text mode. In this mode brik ignores all trailing
empty lines in files. (See more about this below.)

In text mode, brik reads all files line by line, and forces lines to be
terminated by a newline character of constant value before doing a CRC
calculation. Thus, no matter what newline character is used by your system,
the CRC calculation will be unaffected. This means that whether your
operating system uses linefeeds to terminate lines (e.g. **IX), or a carriage
return and a linefeed (e.g. MS-DOS) or a carriage return only (e.g.
Macintosh) or nothing but a record length field (e.g. VAX/VMS), the CRC
calculation in text mode gives the same results.

If a file is not intended to be a text file, the text mode CRC calculated by
brik may not be reliable or the same on all systems for the same file. Brik
can be asked to operate in binary mode by adding a -b option to the option.
Binary mode is applicable only to the -G option, which acts on whole files.
Thus while "brik -G file..." finds whole-file CRCs of all specified files in
text mode, "brik -Gb file ..." does the same in binary mode. In binary mode
brik attempts no newline compensation, but simply reads and calculates the
CRC for all bytes in a file. Provided a file is moved from one system to
another without any changes, brik should calculate the same CRC for it on
both systems.

The output from "brik -Gb" includes a trailing 'b' character in each CRC, so
"brik -C" will correctly use text or binary mode as needed, and -Cb is
equivalent to just -C.


TRAILING EMPTY LINES

The normal behavior of brik in text mode is to ignore any trailing empty lines
in a file when checking or updating the CRC in a Checksum: header. An empty
line is a line that contains nothing, not even blanks or tabs. (Just hitting
a carriage return when you are editing a text file usually produces an empty
line.) If manipulating a text file causes trailing empty lines to be added
or deleted, the CRC calculated by brik will be unaffected.

You can override this if necessary with the -T option, which makes brik
include trailing empty lines in the CRC calculation. For example,
"brik -gWT" will update the Checksum: header with a CRC value that includes
all lines in a text file. Similarly "brik -GT" will find whole-file CRCs
that include all lines in a text file.

When brik is given the -T option, it adds a 'T' suffix to each generated CRC
value. Then, when the CRC is verified with "brik -c" or "brik -C", brik will
correctly include trailing empty lines without having to be explicitly told
to do so.

In binary mode brik always reads all bytes in a file, so it does not ignore
trailing empty lines, and the -T switch is not needed.

The -T and -b options are mutually exclusive, since the first is used only
for text mode and the second is used only for binary mode. If both are
given, whichever is used later overrides the first. This "-bT" is equivalent
to "-T" and "-Tb" is equivalent to "-T".


FILENAME CONVENTIONS

Under MS-DOS and VAX/VMS, wildcards are allowed on the command line and will
be expanded by brik. Under **IX, wildcards are expected to be expanded by
the shell and are not expanded by brik.

If no filename is given, brik reads its standard input. By default this is
keyboard input, but it is expected that input will usually be redirected to
come from a file or a pipe. Also, if a filename is explicitly specified as a
dash ("-"), it stands for standard input.

Thus the following five commands (valid under the **IX operating system)

brik -c myfile # verify "myfile"
brik -c < myfile # verify stdin, which is "myfile"
cat myfile | brik -c # verify stdin, which is a pipe
brik -c - < myfile # verify "-", which is stdin, which is "myfile"
cat myfile | brik -c - # verify "-", which is stdin, which is a pipe

all have the effect of verifying the Checksum: header in the file "myfile".

Standard input can also be read by "brik -C". For example, suppose we have
already given the command

brik -G *.c *.h > crc.lst

to create a file called "crc.lst" that contains a list of whole-file CRCs. We
can now verify the integrity of these files with any of the following
commands:

brik -C crc.lst # read "crc.lst"
brik -C < crc.lst # read stdin, which is "crc.lst"
brik -C - < crc.lst # read "-", which is stdin, which is "crc.lst"
cat crc.lst | brik -C # read stdin, which is a pipe
cat crc.lst | brik -C - # read "-" which is stdin which is a pipe


INDIRECT FILE NAMING

The -f option allows you to have filenames in a list rather than on the
command line. For example, suppose you want to generate whole-file CRCs of
files whose names are selected by some other program. You could use "find"
(under **IX) or "stuff" (under MS-DOS) to generate a list of filenames. When
the -f option is given, brik reads filenames, one per line, from the file(s)
specified. Thus you could do the following:

find . -mtime +3 -print > flist
brik -Gf flist > crc.lst

The first command asks "find" to generate a list of names of all files that
were modified more than 3 days ago, and sends the output to the file "flist".
The contents of "flist" might now look like this, as an example:

./sez.doc
./brik.doc
./stuff.doc
./looz.doc
./fiz.man

The second command above asks brik to read the file called "flist", get a
list of filenames from it, one per line, and generate the whole-file CRC of
each of these files. We additionally redirect the output of "brik -Gf" to
the file called "crc.lst". Given the above contents of "flist", the following
two commands are exactly equivalent:

brik -Gf flist > crc.lst
brik -G ./sez.doc ./brik.doc ./stuff.doc ./looz.doc ./fiz.man > crc.lst

The advantage of the -f option is that once you have filenames in a file,
you need not type them again at the command line. The -f option also allows
you to feed brik filenames generated by another program through a pipe.
Consider this command:

find . -mtime +3 -print | brik -Gf - > crc.lst

Under **IX this concurrently invokes both "find" and brik. As find
generates a filename and sends it to its standard output (a pipe), brik reads
the filename from its standard input and generates its whole-file CRC.
The following pipeline

find . -mtime +3 -print | brik -Gf - | brik -C -

invokes "find" to generate filenames, brik to print the whole-file CRCs of
those files, and brik again to immediately verify them.

Under MS-DOS and VAX/VMS (and any other operating system under which brik has
been installed to expand wildcards itself), a file specified by the -f option
can itself contain wildcards in the filenames. For example, suppose the file
"wildfile" contains the following lines:

/bin/*.exe
/bin/*.com
/doc/*.doc

Now if we invoke brik with the command

brik -Gf wildfile

it will read filespecs from "wildfile", expand wildcards in each filespec,
and generate whole-file CRCs for all matching files.

If you are checking whole-file CRCs with the -C option, you do *not* normally
need to use the -f option, as the -f option introduces an additional level of
file naming indirection. For example, the command

brik -C crc.lst

takes a list of CRCs and filenames from "crc.lst" and verifies them.
However, the command

brik -Cf master.lst

does not do the same thing. Instead, it takes a list of files from
"master.lst", looks inside each of *those* files for a list of CRCs and
filenames, and verifies them.

As an example of the use of -Cf, consider this sequence:

brik -Gb /bin/*.exe > exelist
brik -Gb /bin/*.com > comlist
brik -GT /doc/*.doc > doclist
brik -G /doc/*.man > manlist

Now we have four files called "exelist", "comlist", "doclist", and "manlist"
containing whole-file CRCs of various types. We can test the integrity of
files listed in these in four separate commands like this:

brik -C exelist
brik -C comlist
brik -C doclist
brik -C manlist

But we could also do this in a single step by first creating a file called
"biglist" that contains the names of these four files:

exelist
comlist
doclist
manlist

and then use -Cf thus:

brik -Cf biglist

This causes brik to read filenames from "biglist", look inside each of those
files ("exelist", "comlist", "doclist", and "manlist") and check the CRCs
found there. A **IX example to do the same thing in a more compact
way might be:

cat exelist comlist doclist manlist | brik -Cf -


SILENT VERSUS VERBOSE

Brik accepts options -s and -v that cause it to be more silent or more
verbose than usual.

Normally brik prints a message only if it detects an error. For example,
if you give the command "brik -c *.c *.h" and brik finds that all Checksum:
headers contain CRCs that match the calculated value, it prints nothing.

The -v switch makes brik print a message for each file tested that contains the
word "ok" if stored and calculated CRCs matched and "BAD" if they did not.

In all messages reporting file CRCs, brik prints the actual CRC it calculated,
or a row of question marks if it could not calculate one. Brik fails to
calculate a CRC if it is trying to calculate a header-based CRC (commands
-c and -g) but does not find a Checksum: header in a file.

The -s switch tells brik to be silent. This will cause nothing to be printed
if brik does not find a Checksum header or if CRCs don't match. However, the
status code on exit is still set. The -s option is useful for invoking brik
from within a shell script (**IX) or a batch file (MS-DOS) and later testing
the error code it returned when it exited.

The -s switch does not suppress the error message printed if brik is given a
filename and the file cannot be found. For example, if the command
"brik -cs myfile" is given but "myfile" does not exist, brik will print an
error message even though the -s option was given.


VAX/VMS BUGS

o Under VAX/VMS, file manipulation is unpredictable and the VAX/VMS C
runtime library in particular is very unreliable. One result is that
under VAX/VMS, the -gW option will work only for stream-LF files, which
are the only type of file that VAX/VMS seems to handle correctly.
Fortunately, the -c option will correctly work for VAX/VMS standard
text files.

o The VAX/VMS implementation of brik 1.0 simply ignores filenames that
correspond to nonexistent files instead of giving an error message.
This bug will be fixed as soon as I figure out why wildcard expansion
code that used to work properly with VAX/VMS a year ago doesn't work
any more.

o To avoid annoying error messages, brik under VAX/VMS always exits with
a status code of 1.

o Due to a problem in the VAX/VMS command interpreter, if any uppercase
option characters are typed (e.g. -C, -G, -T), brik will not recognize
them as uppercase unless they are enclosed in double quotes. An
example of a correct command under VAX/VMS:

brik "-GT" *.*

An example of a command that won't work:

brik -GT *.*


PROGRAM LIMITATIONS

Brik 1.0 is designed to work with computer systems that use the 7-bit ASCII
character set and 8-bit bytes with the eighth (parity) bit set to zero.

Brik 1.0 has not been tested with computer systems that use ASCII characters
with the eighth bit set or those that use EBCDIC characters. Although
it will calculate a CRC on such machines, the probability of this CRC being
the same as the one calculated on machines that use 7-bit ASCII is
approximately 0.00000000023.

-- Rahul Dhesi
1989/03/13