(m4.info.gz) Sysval
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12.4 Exit status
================
To see whether a shell command succeeded, use `sysval':
-- Builtin: 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.
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(`exit 2')
=>
sysval
=>2
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.
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
syscmd(`kill -13 $$')
=>
sysval
=>3328
esyscmd(`kill -9 $$')
=>
sysval
=>2304
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