M4(1) M4(1)
NAME
m4 - macro processor
SYNOPSIS
m4 [ options ] [ files ]
DESCRIPTION
M4 is a macro processor intended as a front end for Ratfor,
C, and other languages. Each of the argument files is pro-
cessed in order; if there are no files, or if a file name is
-, the standard input is read. The processed text is writ-
ten on the standard output.
The options and their effects are as follows:
-e Operate interactively. Interrupts are ignored and the
output is unbuffered. Using this mode requires a spe-
cial state of mind.
-s Enable line sync output for the C preprocessor (#line
...)
-Bint
Change the size of the push-back and argument collec-
tion 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.
Macro calls have the form:
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name(arg1,arg2, ..., argn)
The ( must immediately follow the name of the macro. If a
defined macro name is not followed by a (, it is deemed to
have no arguments. Leading unquoted blanks, tabs, and new-
lines are ignored while collecting arguments. Potential
macro names consist of alphabetic letters, digits, and
underscore _, where the first character is not a digit.
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. Macro evalu-
ation proceeds normally during the collection of the argu-
ments, 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 collec-
tion, 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 argu-
ments; $* is replaced by a list of all the argu-
ments 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 second argument, otherwise the third. If
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there is no third argument, the value is null.
The word unix is predefined on UNIX 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 per-
formed.
changequote change quote symbols to the first and second
arguments. The symbols may be up to five char-
acters 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 argu-
ment 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 includ-
ing the next new-line.
ifelse has three or more arguments. If the first argu-
ment 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. Oth-
erwise, the value is either the fourth string,
or, if it is not present, null.
incr returns the value of its argument incremented by
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1. The value of the argument is calculated by
interpreting an initial digit-string as a deci-
mal number.
decr returns the value of its argument decremented by
1.
eval evaluates its argument as an arithmetic expres-
sion, using 32-bit arithmetic. Operators
include +, -, *, /, %, ^ (exponentiation), bit-
wise &, |, ^, 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 argu-
ment.
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 select-
ing the first character; the third argument
indicates the length of the substring. A miss-
ing third argument is taken to be large enough
to extend to the end of the first string.
translit transliterates the characters in its first argu-
ment 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 UNIX 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 XXXXX in its argument with
the current process ID.
m4exit causes immediate exit from m4. Argument 1, if
given, is the exit code; the default is 0.
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m4wrap argument 1 will be pushed back at final EOF;
example: m4wrap(`cleanup()')
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 mac-
ros (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.
SEE ALSO
The M4 Macro Processor by B. W. Kernighan and D. M. Ritchie.