Say you have a `function' named _streamRevert that takes two arguments. The first argument is the number of the stream to collect, the second argument is the number of the stream to which to dump the collected stream. To accomplish this, you make use of four auxiliary functions: SAVE, push_divert, pop_divert, and _streamDump. Their definitions are as follows:
define(`push_divert',` `'pushdef(`savedivert',divnum)dnl `'divert($1)dnl `'pushdef(`lastdivnum',divnum)dnl ') define(`pop_divert',` `'divert(savedivert)dnl `'popdef(`savedivert')dnl ') define(`SAVE',` `'push_divert($2)$1`'pop_divert()dnl ') define(`_streamDump',``esyscmd'(`echo 'undivert($1)` > /dev/fd/0')') The definition of _streamRevert is here: define(`_streamRevert',` `'`SAVE'(`_streamDump(`$1')',$2)') And you can call it to SAVE the output in diversion 2 into diversion 3, e.g.,: _streamRevert(2,3) but _streamRevert() outputs: `'`SAVE'(`_streamDump(`2')',3)' after the arguments are collected. m4 then strips the quotes around this output and does not evaluate the expression. *This is not a problem*. To get around this quality of quotes, an _echo function can be written to re-send the output of a function (i.e., re-send the output of _streamRevert and rescan it) to stdin: pushdef(`_echo',`esyscmd($1 > /dev/fd/0)') This works. It is used like so: _echo(_streamRevert(2,3)) So here is the issue. The operation of these functions works perfectly until esyscmd is called from _streamDump. esyscmd sees ``esyscmd'(`echo 'undivert(2)` > /dev/fd/0')' and then expands undivert(2), but SAVE only sees ` `'push_divert(3)esyscmd(echo > /dev/fd/0)`'pop_divert()dnl ' How do you get esyscmd to collect the result of the expansion of undivert($1) as an argument to esyscmd? Right now it seems like esyscmd expands undivert($1) but does not capture the result of the expansion as an argument. Note: to SAVE something in a stream, use SAVE(value,target). e.g., SAVE(`Lorem ipsum dolor sit amet',2) Which pushes the value into divert(2)
