Re^3: system and $?

If myprog.exe can not be run, system(...) returns on my platform 256 (which is exit code 1, no child-error), and, as you point out, sets $! to some error code.

You have a broken Perl if that's true.

If myprog can not be run, system sets $? to -1 and sets the error in $!.

If a shell command cannot be run, system sets $? to something other than -1 (since the shell was successfully executed) and $! contains no meaningful information. The shell cannot possibly change the parent's errno.

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Re^4: system and $? by Anonymous Monk on Aug 26, 2009 at 14:07 UTC
By that logic, all windows perls are broken, which may or may not be true.	[reply]
Re^5: system and $? by ikegami (Patriarch) on Aug 26, 2009 at 14:12 UTC
It is broken in the sense that the shell is needlessly invoked. It probably does that because people expect `dir` to work. (`dir` is a shell command, not an executable.) But it does behave correctly for the shell being invoked. `>perl -le"system 'foo'; print $?==-1 ? qq{$!=\$!} : qq{\$?=$?}" 'foo' is not recognized as an internal or external command, operable program or batch file. $?=256` [download] Unfortunately, that's all the information to which you have access. `$!` is meaningless. Conveniently, it does print an error message to STDERR. Update: This is even odder: `>perl -le"system({ 'foo' } 'foo'); print $?==-1 ? qq{$!=\$!} : qq{\$?= +$?}" $?=65280` [download]	[reply] [d/l] [select]
Re^4: system and $? by rovf (Priest) on Aug 26, 2009 at 14:18 UTC
You have a broken Perl if that's true. Well, it's pretty easy to reproduce, and the effect is the same in ActiveState 5.8.8 und 5.10. If I find the time, I'll try it with Strawberry... The shell cannot possibly change the parent's errno. Certainly not. It would need to communicate the information in a different way to the parent process. Well, this is a theoretical question, because Perl - likely in order to be portable - is not programmed that way, but: If it would be possible on Windows to somehow get the full (i.e. 32 Bit) Exitcode, we could use this information: If the shell can't execute a program, it sets this exitcode to 9009. OTOH, this would still make it indistinguishable from a program which deliberately sets that exit code.. -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l]
Re^5: system and $? by ikegami (Patriarch) on Aug 26, 2009 at 14:22 UTC
Well, it's pretty easy to reproduce, and the effect is the same in ActiveState 5.8.8 und 5.10. I used ActivePerl 5.10.0 b1005 above. 5.8.8 gives the same result. Both successfully execute the shell, so `$?` is not `-1`, so `$!` is meaningless. OTOH, this would still make it indistinguishable from a program which deliberately sets that exit code.. Yes.	[reply] [d/l] [select]