Dec 192017
M4 is a MSDOS version of the Unix m4 macro processor. C source included.
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M4 is a MSDOS version of the Unix m4 macro processor. C source included.
File Name File Size Zip Size Zip Type
C.M4 470 221 deflated
EXAMPLE.BAT 657 292 deflated
EXAMPLE.C4 529 274 deflated
M4.DOC 12800 3865 deflated
M4.EXE 16566 10348 deflated
SOURCE.ZIP 11086 10492 deflated

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Contents of the M4.DOC file

M4.DOC 12 November 86 Page 1

Copyright 1986 Michael M Rubenstein

M4 is a MSDOS version of the Unix (tm) m4 macro processor. All
functions of the Unix version 7 m4 are supported as well as a
number of extensions. This version was written without reference
to the Unix source and should not be expected to match the Unix
version if used in an undocumented manner.

M4 requires MSDOS or PCDOS version 2.0 or higher. No particular
IBM compatibility should be required.


M4 is invoked with the command

m4 [...]

For example, to apply m4 to the files file1.m4 file2 file3.fil,
the command

m4 file1.m4 file2 file3.fil

is used. Output is always to stdout, which is usually
redirected. If no input files are given, input is taken from
stdin. Any of the input files may be specified as -, in which
case it is taken from stdin.


M4 reads one or more text files and writes the modified output to
stdout (which may, of course, be redirected). When a macro is
encountered, it is evaluated and the result is rescanned. Text
may be quoted by enclosing it in `' (note that these are not the
same character). When quoted text is encountered, the quotes are
removed and the text is not scanned for macros. However, if the
text is used in a macro evaluation and is rescanned, macro
substitution will take place. Quotes may be nested to allow text
to be rescanned several times without evaluation.

The "define" built in macro permits definition of new macros.
For example

define(A, 3)

defines A to be 3. No space is permitted between the macro name,
"define", and the left parenthesis. If a macro name is not
followed immediately by a left parenthesis, it has no arguments.

Macro names consist of letters, underscores, and digits and must
begin with a letter or underscore. Case is significant. Macro
names are recognized only when they appear as words (i.e.,

M4.DOC 12 November 86 Page 2

surrounded by characters which may not appear in a macro name).

Macros are expanded at the earliest opportunity. Therefore, the

define(A, 3)
define(B, A)

would define A and B as 3. However, since the "A" in the second
line is replaced by 3 before definition takes place, changing the
value of A will not affect B. If the order of the definitions
were changed to

define(B, A)
define(A, 3)

the value of B would change with that of A (actually, B would be
replaced by A which would then be replaced by it's value, 2).

Alternatively, one could

define(A, 3)
define(B, `A')

The quotes prevent A from being evaluated in the second line, so
B is again defined as A. In general, quoting the second argument
of "define" is useful to prevent evaluation before definition.

M4 always strips off one level of quotes when it evaluates
something. Thus, if one wishes to use the word "define" in the
text, it must be quoted.

int `define';

will be changed to

int define;

by M4.

Quoting is necessary when redefining a macro. For example, the

define(A, 2)
define(A, 3)

would leave A defined as 2 since the second line would expand to

define(2, 3)

The proper sequence is

define(A, 2)
define(`A', 3)

M4.DOC 12 November 86 Page 3

Macros may have arguments. The definition

define(sum, `($1 + $2)')

could be used to generate code to add two numbers. For example,

sum(a, 3)

would generate

(a + 3)

Omitted arguments are replaced by a null string, so


would generate

(a +)

Excess arguments are ignored.

A macro may use up to 9 arguments, $1, $2, ..., $9. $0 is the
name of the macro.

Software Tools (B. W. Kernighan and P. J. Plauger, Addison-
Wesley, Inc., 1976) contains a similar macro processor and much
more extensive discussion of it's usage.

Built In Macros

Defines up to 4 pairs of alternate quotes. Alternate quotes
prevent scanning for macros, but, unlike regular quotes, are
not removed from the text. Default is no alternate quotes.
This is an extension in this version of M4. It's primary
purpose is to prevent evaluation of macros in strings of a
language being preprocessed.

changequote(, )
Changes the quote characters. Default quotes are `'.

Changes the argument flag character (default "$"). Note
that the argument flag character is processed at expansion
time, not at definition time. This can lead to strange
results if this macro appears after any definitions.

Changes the comment character (default #). All input
from a comment character to the end of the line is simply
passed to the output. If no argument, there will be no
comment character.

M4.DOC 12 November 86 Page 4

- 1

Defines to as . Up to 9 arguments may be
used. Arguments are referenced in the definition ()
by preceding a digit (1-9) by a special character (default
"$"). Argument 0 is the name of the macro.

See also, changearg.

Sends output to diversion file if is
from 1 to 9. Restores normal output if is 0 or
omitted. Ignores output if is outside of the
range 0 through 9.

Diversions are normally copied to the output in numeric
order after all input. This can be modified by undivert

The number of the currently active diversion. 0 if no

Deletes all characters through the next newline. This is
useful for preventing excess new lines from being translated
during definition. For example, the sequence

define(A, something)
define(B, somethingelse)

will be translated into two new lines. By adding "dnl" to
the end of each line, this can be prevented.

Displays the definitions of , etc. on stderr. For
obvious reasons, , etc. should usually be quoted. If
there are no arguments, all definitions are displayed.

Prints to stderr. is as in C fprintf. This will
not be meaningful if contains any non-string format

The evaluation of the integer expression .
Permitted operators in decreasing order of precedence are

+ (unary), - (unary)
*, /, %
+ (binary), - (binary)
==, !=, <, <=, >, >=

M4.DOC 12 November 86 Page 5

& or &&
| or ||

Note that "&" and "&&" are equivalent, as are "|" and "||".
"a && b" gives 1 if both a and b are nonzero, 0 otherwise.
"a || b" gives 1 if either a or b is nonzero, 1 otherwise.
Unlike the similar C expressions, however, evaluation is not
stopped once the value can be determined.

If is defined then else . For
obvious reasons, should usually be quoted.

If = then else .

can be replaced by ,,,,
in which case the result is

if = then
else if = then

This can be extended in the obvious manner.

The contents of the file . It is an error for
not to exist. See also sinclude.

+ 1

The position (origin 0) in where begins.
-1 if does not occur in .

The length of .

Defines the macro character. Macros will only be recognized
if preceded by the macro character. Note that this only
applies to macro invocations. The macro character is not
used in the definition of a macro. If no argument, macros
will always be recognized. For example, to define `this' as
`that' when the macro character is &, the definition would

&define(`this', `that')

"&this" would be changed to "that", but "this" would be

M4.DOC 12 November 86 Page 6

Generates a unique filename. String should contain a
substring of several "X"s which are changed in such a way
the result is a unique file name.

Defined as null. The Unix version defines "unix" as null,
so a macro script can determine the operating environment.

Removes the definitions of all built in macros. Deletes all
characters through the next newline.

This is an extension in this version of M4 to facilitate use
as a preprocessor.

The contents of the file . If does not
exist, null. See also include.

The substring of starting at position
(origin 0) and length . If is omitted, the
result is the rest of the string.

The operating system command is executed.

with characters in replaced by the
corresponding characters in . If is
shorter than , characters without an entry in
are deleted.

Removes the definition of . For obvious reasons,
should usually be quoted.

Copies (and empties) diversion . If is
omitted, all diversions are copied. The diversions are not
rescanned for macros.

For the Hacker

Source code is provided. M4 was compiled with Aztec C, but it
should be very easy to modify for other C compilers.


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