Info Catalog m4: Esyscmd m4: Shell commands m4: Mkstemp

m4: Sysval

 
 13.4 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.
 
      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
      syscmd(`kill -9 $$')
      =>
      sysval
      =>2304
      syscmd()
      =>
      sysval
      =>0
      esyscmd(`kill -9 $$')
      =>
      sysval
      =>2304
 

Info Catalog m4: Esyscmd m4: Shell commands m4: Mkstemp