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To see whether a shell command succeeded, use sysval:
Expands to the exit status of the last shell command run with
syscmd or esyscmd. Expands to 0 if no command has been
run yet.
sysval ⇒0 syscmd(`false') ⇒ ifelse(sysval, `0', `zero', `non-zero') ⇒non-zero syscmd(`exit 2') ⇒ sysval ⇒2 syscmd(`true') ⇒ sysval ⇒0 esyscmd(`false') ⇒ ifelse(sysval, `0', `zero', `non-zero') ⇒non-zero esyscmd(`echo dnl && exit 127') ⇒ sysval ⇒127 esyscmd(`true') ⇒ sysval ⇒0
sysval results in 127 if there was a problem executing the
command, for example, if the system-imposed argument length is exceeded,
or if there were not enough resources to fork. It is not possible to
distinguish between failed execution and successful execution that had
an exit status of 127, unless there was output from the child process.
On UNIX platforms, where it is possible to detect when command execution is terminated by a signal, rather than a normal exit, the result is the signal number shifted left by eight bits.
dnl This test assumes kill is a shell builtin, and that signals are
dnl recognizable.
ifdef(`__unix__', ,
`errprint(` skipping: syscmd does not have unix semantics
')m4exit(`77')')dnl
changequote(`[', `]')
⇒
syscmd([/bin/sh -c 'kill -9 $$'; st=$?; test $st = 137 || test $st = 265])
⇒
ifelse(sysval, [0], , [errprint([ skipping: shell does not send signal 9
])m4exit([77])])dnl
syscmd([kill -9 $$])
⇒
sysval
⇒2304
syscmd()
⇒
sysval
⇒0
esyscmd([kill -9 $$])
⇒
sysval
⇒2304