m4(1) UNIX Programmer's Manual m4(1) NAME m4 - macro processor SYNOPSIS m4 [ -Dname[=value]] [-Uname] [files ...] DESCRIPTION _m_4 is a macro processor intended as a front end for any language (e.g., C, ratfor, fortran, lex, and yacc). _m_4 reads from the standard input and writes the processed text to the standard output. Each of the optional argument files is processed in order. 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 `(', 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 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 effec- tive as those in the original input text. After argument collection, the value of the macro is pushed back onto the input stream and rescanned. -Dname[=value] Define the symbol name to have some value (or NULL). -Uname Undefine the symbol name. _m_4 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 Printed 11/26/99 April 14, 1994 1 m4(1) UNIX Programmer's Manual m4(1) arguments are replaced by the null string. undefine removes the definition of the macro named in its argument. 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. changecom Change the start and end comment sequences. The default is the pound sign '#' and the newline character. With no arguments comments are turned off. The maximum legnth for a comment marker is five characters. changequote Change quote characters to the first and second arguments. _C_h_a_n_g_e_q_u_o_t_e without arguments restores the original values (i.e., `'). decr Decrements the argument by 1. The argument must be a valid numeric string. divert _m_4 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 _d_i_v_e_r_t macro changes the current output stream to its (digit-string) argu- ment. 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 argu- ment. Text may be undiverted into another diver- sion. Undiverting discards the diverted text. defn Returns the quoted definition for each argument. This can be used to rename macro definitions (even for builtin macros). divnum returns the value of the current output stream. dnl reads and discards characters up to and including the next newline. expr This is an alias for eval. 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. Otherwise, Printed 11/26/99 April 14, 1994 2 m4(1) UNIX Programmer's Manual m4(1) 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. eval evaluates its argument as an arithmetic expres- sion, using 32-bit arithmetic. Operators include +, -, *, /, %, ^ (exponentiation); relationals; parentheses. len returns the number of characters in its argument. m4exit Immediately exits with the return value specified by the first argument, 0 if none. m4wrap Allows you to define what happens at the final EOF, usually for cleanup purposes. (e.g., m4wrap("cleanup(tempfile)") causes the macro cleanup to be invoked after all processing is done.) 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 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 _i_n_c_l_u_d_e, except that it says noth- ing if the file is inaccessible. syscmd executes the UNIX command given in the first argu- ment. No value is returned. maketemp fills in a string of XXXXX in its argument with the current process id. Printed 11/26/99 April 14, 1994 3 m4(1) UNIX Programmer's Manual m4(1) paste Includes the contents of the file specified by the first argument without any macro processing. Aborts with an error message if the file cannot be included. popdef Restores the pushdef'd definition for each argu- ment. pushdef Takes the same arguments as define, but it saves the definition on a stack for later retrieval by popdef. shift Returns all but the first argument, the remaining 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. spaste Similar to paste, except it ignores any errors. syscal Returns the return value from the last syscmd. 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. unix A pre-defined macro for testing the OS platform. SEE ALSO B. W. Kernighan and D. M. Ritchie, _T_h_e _m_4 _M_a_c_r_o _P_r_o_c_e_s_s_o_r HISTORY An m4 command appeared in Version 6 AT&T UNIX. AUTHOR Ozan Yigit Printed 11/26/99 April 14, 1994 4