NAME

m4 − macro processor

SYNOPSIS

m4 [ files ]

DESCRIPTION

M4 is a macro processor intended as a front end for Ratfor, C, and other languages.  It processes each of the argument files in order.  If there are no arguments, or if an argument is ‘−’, m4 reads the standard input.  The processed text is written on the standard output. 

Macro calls have the form

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

The ‘(’ must immediately follow the name of the macro.  If a defined macro name is not followed by a ‘(’, m4 considers it to have no arguments.  M4 ignores leading unquoted blanks, tabs, and newlines 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 m4 recognizes a macro name, it collects the macro’s arguments by searching for a matching right parenthesis.  Macro evaluation proceeds normally during the collection of the arguments.  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, m4 pushes the value of the macro back onto the input stream, then rescans the value.  M4 Macros

M4 makes available the following built-in macros.  The macros may be redefined; once redefined, however, the macros lose their original meanings.  Their values are null unless otherwise stated. 

changequote
Change quote characters to the first and second arguments. Changequote without arguments restores the original values (i.e., `´).

define Installs the second argument 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.

divert Changes the current output stream to its (digit-string) argument.  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.  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. 

eval Evaluates its argument as an arithmetic expression, using 32-bit arithmetic.  Operators include +, −, ∗, /, %, ^ (exponentiation); relationals; parentheses. 

ifdef Sets the value to the second argument if the first argument is defined; otherwise, m4 sets the value to the third argument.  If there is no third argument, the value is null.  The word unix is predefined on UNIX versions of m4. 

ifelse Takes 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. 

maketemp
Fills in a string of XXXXX in its argument with the current process id.

sinclude 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 Executes the UNIX command given in the first argument.  No value is returned. 

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. 

undefine Removes the definition of the macro named in its argument. 

undivert Causes immediate output of text from diversions named as arguments.  Without an argument, causes output of text from all diversions.  You can undivert the text into another diversion.  Undiverting discards the diverted text. 

SEE ALSO

B. W. Kernighan and D. M. Ritchie, The M4 Macro Processor

INTEGRATED SOLUTIONS 4.3 BSD  —  April 29, 1985