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Updated: Thursday, June 13, 2019
 
 

m4(1)

Name

m4 - macro processor

Synopsis

/usr/bin/m4 [-e] [-s] [
-B int] [-H 
int] [-S int] 
     [-T int] [-D
name [=val]] ... [-U 
name] ... [file]...
/usr/xpg4/bin/m4 [-e] [-s
] [-B int] [-H 
int] [-S int] 
     [-T int] [-D
name [...=val]] [-U 
name] ... [file]...

Description

The m4 utility 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 is , the standard input is read. The processed text is written on the standard output. Note: m4 cannot include more than nine nested files and writes a diagnostic message if that number is exceeded.

Macro Syntax

Macro calls have the form:

name(arg1,
arg2, ..., argn)

The open parenthesis character, (, 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 underscore (_), where the first character is not a digit.

Leading unquoted blanks, TABs, and NEWLINEs 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.

Macro Processing

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.

Options

The options and their effects are as follows:

–Bint

Changes the size of the push-back and argument collection buffers from the default of 4,096. Values of size less than or equal to zero are ignored and the default value is used.

–e

Operates interactively. Interrupts are ignored and the output is unbuffered.

–Hint

Changes the size of the symbol table hash array from the default of 199. For better performance, the size should be prime. Values of size less than or equal to zero are ignored and the default value is used.

–s

Enables line sync output for the C preprocessor (#line . . . )

–Sint

Changes the size of the call stack from the default of 100 slots. Macros take three slots, and non-macro arguments take one. Values of size less than or equal to zero are ignored and the default value is used.

–Tint

Changes the size of the token buffer from the default of 512 bytes. Values of size less than or equal to zero are ignored and the default value is used.

To be effective, the above flags must appear before any file names and before any –D or –U flags:

–D name[= val]

Defines name to val or to NULL in val's absence.

–Uname

Undefines name.

Operands

The following operand is supported:

file

A path name of a text file to be processed. If no file is given, or if it is −, the standard input is read.

Usage

The m4 utility makes available the following built-in macros. These macros can be redefined, but once this is done the original meaning is lost. Their values are NULL unless otherwise stated.

changequote

Change quote symbols to the first and second arguments. The symbols can be up to five characters long. changequote without arguments restores the original values (that is, ` ').

changecom

Change left and right comment markers from the default # and NEWLINE. With no arguments, the comment mechanism is effectively disabled. With one argument, the left marker becomes the argument and the right marker becomes NEWLINE. With two arguments, both markers are affected. Comment markers can be up to five characters long.

decr

Returns the value of its argument decremented by 1.

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).

defn

Returns the quoted definition of its argument(s). It is useful for renaming macros, especially built-ins.

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.

divnum

Returns the value of the current output stream.

dnl

Reads and discards characters up to and including the next NEWLINE.

dumpdef

Prints current names and definitions, for the named items, or for all if no arguments are given.

errprint

Prints its argument on the diagnostic output file.

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.

ifelse

This macro 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.

include

Returns the contents of the file named in the argument.

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.

index

Returns the position in its first argument where the second argument begins (zero origin), or −1 if the second argument does not occur.

len

Returns the number of characters in its argument.

m4exit

This macro causes immediate exit from m4. Argument 1, if given, is the exit code; the default is 0.

m4wrap

Argument 1 is pushed back at final EOF. Example: m4wrap(`cleanup( )')

maketemp

Obsolete. Fills in a string of “X” characters in its argument with the current process ID.

mkstemp

The first argument shall be taken as a template for creating an empty file, with trailing “X” characters replaced with characters from the portable filename character set. The behavior is unspecified if the first argument does not end in at least six “X” characters. If a temporary file is successfully created, then the defining text of the macro is the name of the new file. The user ID of the file should be set to the effective user ID of the process. The group ID of the file should be set to the group ID of the file's parent directory or to the effective group ID of the process. The file access permission bits are set such that only the owner can both read and write the file, regardless of the current umask of the process. If a file could not be created, the defining text of the macro should be the empty string. The behavior is unspecified if mkstemp is not immediately followed by a <left-parenthesis>.

popdef

Removes current definition of its argument(s), exposing the previous one, if any.

pushdef

Like define, but saves any previous definition.

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 is subsequently be performed.

sinclude

This macro is identical to include, except that it says nothing if the file is inaccessible.

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.

syscmd

This macro executes the command given in the first argument. No value is returned.

sysval

This macro is the return code from the last call to syscmd .

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.

traceon

This macro 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.

undefine

Removes the definition of the macro named in its argument.

undivert

This macro causes immediate output of text from diversions named as arguments, or all diversions if no argument. Text can be undiverted into another diversion. Undiverting discards the diverted text.

/usr/bin/m4

eval

Evaluates its argument as an arithmetic expression, using 32-bit signed-integer arithmetic. The following operators are supported: parentheses, unary -, unary +, !, ~, *, /, %, +, -, relationals, bitwise &, |, &&, and ||. Octal and hex numbers can be specified as in C. The second argument specifies the radix for the result; the default is 10. The third argument can be used to specify the minimum number of digits in the result.

/usr/xpg4/bin/m4

eval

Evaluates its argument as an arithmetic expression, using 32-bit signed-integer arithmetic. The following operators are supported: parentheses, unary -, unary +, !, ~, *, /, %, +, -, <<, >>, relationals, bitwise &, |, &&, and ||. Precedence and associativity are as in C. Octal and hex numbers can also be specified as in C. The second argument specifies the radix for the result; the default is 10. The third argument can be used to specify the minimum number of digits in the result.

Examples

Example 1 Examples of m4 files

If the file m4src contains the lines:


The value of `VER' is "VER".
        ifdef(`VER', ``VER'' is defined to be VER., VER is not defined.)
        ifelse(VER, 1, ``VER'' is `VER'.)
        ifelse(VER, 2, ``VER'' is `VER'., ``VER'' is not 2.)
        end

then the command:

m4 m4src

or the command:

m4 -U VER m4src

produces the output:


The value of VER is "VER".
        VER is not defined.

        VER is not 2.
        end

The command:

m4 -D VER m4src

produces the output:


The value of VER is "".
        VER is defined to be .

        VER is not 2.
        end

The command:

m4 -D VER=1 m4src

produces the output:


The value of VER is "1".
       VER is defined to be 1.
       VER is 1.
       VER is not 2.
       end

The command:

m4 -D VER=2 m4src

produces the output:


The value of VER is "2".
        VER is defined to be 2.

        VER is 2.
        end

Environment Variables

See environ(7) for descriptions of the following environment variables that affect the execution of m4: LANG, LC_ALL, LC_CTYPE , LC_MESSAGES, and NLSPATH.

Exit Status

The following exit values are returned:

0

Successful completion.

>0

An error occurred

If the m4exit macro is used, the exit value can be specified by the input file.

Attributes

See attributes(7) for descriptions of the following attributes:

/usr/bin/m4

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/core-os

/usr/xpg4/bin/m4

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Availability
system/xopen/xcu4
Interface Stability
Committed
Standard

See Also

as(1), attributes(7), environ(7), standards(7)