m4(1) USER COMMANDS m4(1)
NAME
m4 - macro processor
SYNOPSIS
m4 [options] [files]
DESCRIPTION
The m4 command is a macro processor intended as a front end
for C, assembler, 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 col-
lection 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, the above 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:
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 alphanumeric characters and under-
score (), where the first character is not a digit.
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m4(1) USER COMMANDS m4(1)
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 that 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. These
macros 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
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 second argument, otherwise the third. If
there is no third argument, the value is null.
The word unix is predefined.
shift returns all but its first argument. The other
arguments are quoted and pushed back with
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m4(1) USER COMMANDS m4(1)
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 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
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 includ-
ing 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 pro-
cess 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 number.
decr returns the value of its argument decremented
by 1.
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m4(1) USER COMMANDS m4(1)
eval evaluates its argument as an arithmetic expres-
sion, using 32-bit arithmetic. Operators
include +, -, *, /, %, ** (exponentiation),
bitwise &, |, ^, and ~; relationals;
parentheses. Octal and hex numbers may be
specified as in C. The second argument speci-
fies 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
argument from the set given by the second argu-
ment to the set given by the third. No abbre-
viations 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 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 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.
m4wrap argument 1 will be pushed back at final EOF;
example: m4wrap(`cleanup()')
errprint prints its argument on the diagnostic output
file.
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m4(1) USER COMMANDS m4(1)
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 tra-
ceon can be untraced only by specific calls to
traceoff.
SEE ALSO
as(1), cc(1).
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