m4(1)
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m4 Command
macro processor
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SYNTAX
m4 [ options ] [ files ]
DESCRIPTION
M4 is a macro processor intended as a front end for C and other
languages. Each of the argument files is processed in order; if
there are no files, or if a file name is -, the standard input is
read. The processed text is written on the standard output.
The options and their effects are as follows:
-e Operate interactively. Interrupts are ignored and the
output is unbuffered.
-s Enable line sync output for the C preprocessor (#line ...)
-Bint
Change the size of the push-back and argument collection
buffers from the default of 4,096.
-Hint
Change the size of the symbol table hash array from the
default of 199. The size should be prime.
-Sint
Change the size of the call stack from the default of 100
slots. Macros take three slots, and non-macro arguments
take one.
-Tint
Change the size of the token buffer from the default of 512
bytes.
To be effective, these flags must appear before any file names
and before any -D or -U flags:
-Dname[=val]
Defines name to val or to null in val's absence.
-Uname
undefines name.
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Macro calls have the form:
name(arg1,arg2, ..., argn)
The ( must immediately follow the name of the macro. If the name
of a defined macro is not followed by a (, it is deemed to be a
call of that macro with no arguments. Potential macro names
consist of alphabetic letters, digits, and underscore (), where
the first character is not a digit.
Leading unquoted blanks, tabs, and new-lines are ignored while
collecting arguments. Left and right single quotes are used to
quote strings. The value of a quoted string is the string
stripped of the quotes.
When a macro name is recognized, its arguments are collected by
searching for a matching right parenthesis. If fewer arguments
are supplied than are in the macro definition, the trailing
arguments are taken to be null. Macro evaluation proceeds
normally during the collection of the arguments, and any commas
or right parentheses which happen to turn up within the value of
a nested call are as effective as those in the original input
text. After argument collection, the value of the macro is
pushed back onto the input stream and rescanned.
M4 makes available the following built-in macros. They may be
redefined, but once this is done the original meaning is lost.
Their values are null unless otherwise stated.
define the second argument is installed as the value of the
macro whose name is the first argument. Each
occurrence of $n in the replacement text, where n is
a digit, is replaced by the n-th argument. Argument
0 is the name of the macro; missing arguments are
replaced by the null string; $# is replaced by the
number of arguments; $* is replaced by a list of all
the arguments separated by commas; $@ is like $*, but
each argument is quoted (with the current quotes).
undefine removes the definition of the macro named in its
argument.
defn returns the quoted definition of its argument(s). It
is useful for renaming macros, especially built-ins.
pushdef like define, but saves any previous definition.
popdef removes current definition of its argument(s),
exposing the previous one, if any.
ifdef if the first argument is defined, the value is the
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second argument, otherwise the third. If there is no
third argument, the value is null. The word unix is
predefined on UNIX system versions of m4.
shift returns all but its first argument. The other
arguments are quoted and pushed back with commas in
between. The quoting nullifies the effect of the
extra scan that will subsequently be performed.
changequote change quote symbols to the first and second
arguments. The symbols may be up to five characters
long. Changequote without arguments restores the
original values (i.e., `').
changecom change left and right comment markers from the
default # and new-line. With no arguments, the
comment mechanism is effectively disabled. With one
argument, the left marker becomes the argument and
the right marker becomes new-line. With two
arguments, both markers are affected. Comment
markers may be up to five characters long.
divert m4 maintains 10 output streams, numbered 0-9. The
final output is the concatenation of the streams in
numerical order; initially stream 0 is the current
stream. The divert macro changes the current output
stream to its (digit-string) argument. Output
diverted to a stream other than 0 through 9 is
discarded.
undivert causes immediate output of text from diversions named
as arguments, or all diversions if no argument. Text
may be undiverted into another diversion.
Undiverting discards the diverted text.
divnum returns the value of the current output stream.
dnl reads and discards characters up to and including the
next new-line.
ifelse has three or more arguments. If the first argument
is the same string as the second, then the value is
the third argument. If not, and if there are more
than four arguments, the process is repeated with
arguments 4, 5, 6 and 7. Otherwise, the value is
either the fourth string, or, if it is not present,
null.
incr returns the value of its argument incremented by 1.
The value of the argument is calculated by
interpreting an initial digit-string as a decimal
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number.
decr returns the value of its argument decremented by 1.
eval evaluates its argument as an arithmetic expression,
using 32-bit arithmetic. Operators include +, -, *,
/, %, ^ (exponentiation), bitwise &, |, ^, and ~;
relationals; parentheses. Octal and hex numbers may
be specified as in C. The second argument specifies
the radix for the result; the default is 10. The
third argument may be used to specify the minimum
number of digits in the result.
len returns the number of characters in its argument.
index returns the position in its first argument where the
second argument begins (zero origin), or -1 if the
second argument does not occur.
substr returns a substring of its first argument. The
second argument is a zero origin number selecting the
first character; the third argument indicates the
length of the substring. A missing third argument is
taken to be large enough to extend to the end of the
first string.
translit transliterates the characters in its first argument
from the set given by the second argument to the set
given by the third. No abbreviations are permitted.
include returns the contents of the file named in the
argument.
sinclude is identical to include, except that it says nothing
if the file is inaccessible.
syscmd executes the DG/UX system command given in the first
argument. No value is returned.
sysval is the return code from the last call to syscmd.
maketemp fills in a string of XXXXXX at the end of its
argument with a unique letter and the current process
ID.
m4exit causes immediate exit from m4. Argument 1, if given,
is the exit code; the default is 0.
m4wrap argument 1 will be pushed back at final EOF; example:
m4wrap(`cleanup()')
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errprint prints its argument on the diagnostic output file.
dumpdef prints current names and definitions, for the named
items, or for all if no arguments are given.
traceon with no arguments, turns on tracing for all macros
(including built-ins). Otherwise, turns on tracing
for named macros.
traceoff turns off trace globally and for any macros
specified. Macros specifically traced by traceon can
be untraced only by specific calls to traceoff.
EXAMPLE
m4 file1 file2 > outputfile
will run the m4 macro processor on the files file1 and file2,
redirecting the output into outputfile.
SEE ALSO
cc(1), cpp(1).
The M4 Macro Processor by B. W. Kernighan and D. M. Ritchie.
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