Return code from calling qx

f50bodykit has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Return code from calling qx by ikegami (Patriarch) on Oct 27, 2009 at 19:19 UTC
The docs clearly answers your question. $? is The status returned by the last pipe close, backtick (``) command, successful call to wait() or waitpid(), or from the system() operator. This is just the 16-bit status word returned by the traditional Unix wait() system call (or else is made up to look like it). Thus, the exit value of the subprocess is really ($? >> 8), and $? & 127 gives which signal, if any, the process died from, and $? & 128 reports whether there was a core dump. (Mnemonic: similar to sh and ksh.)	[reply]
Re^2: Return code from calling qx by Argel (Prior) on Oct 28, 2009 at 00:16 UTC
The docs may explain it, but trying Googling for qq{perl "$? >> 8"} sometime. Google doesn't even honor the phrase so the results are not that impressive. On Google it's hard if not impossible to search for "$? >> 8? -- try it without "perl" and you will get links to the number 8 because Google is not searching on the phrase even though it is in quotes (probably too many special characters). One more reason not to like the five bazillion special two character variables Perl has (of course, when typing them in, most of us really like them! :-) Elda Taluta; Sarks Sark; Ark Arks	[reply]
Re^3: Return code from calling qx by ikegami (Patriarch) on Oct 28, 2009 at 03:13 UTC
I fail to see your point, especially since "special perl variables" turns up the very text I quoted in the first result.	[reply]
Re^4: Return code from calling qx by Argel (Prior) on Oct 28, 2009 at 18:29 UTC
Re^4: Return code from calling qx by SuicideJunkie (Vicar) on Oct 28, 2009 at 13:45 UTC
Re: Return code from calling qx by Corion (Patriarch) on Oct 27, 2009 at 19:06 UTC
See the documentation of qx, or "backticks" as `` also are called. Also, system might have more documentation on it.	[reply] [d/l]
Re: Return code from calling qx by jettero (Monsignor) on Oct 27, 2009 at 19:28 UTC
Corion and ikegami are correct. But I can never remember all the weird little things with qx and system (et al); so I just use IPC::System::Simple and all my problems are solved for me. -Paul	[reply]
Re: Return code from calling qx by gmargo (Hermit) on Oct 27, 2009 at 19:34 UTC
See also the 'system' function details in perlport. There they discuss why you should not use the hard coded constants, but instead use the WIFEXITED and WEXITVALUE macros provided by POSIX. This was discussed in a recent thread 801643 regarding interpreting the results of waitpid.	[reply]
Re: Return code from calling qx by f50bodykit (Initiate) on Oct 27, 2009 at 19:54 UTC
Thanks everyone I found all of your refrences helpful. I'm having trouble understanding shift operators. When I run `qx(dir thisdoesntexist); print $?;` [download] I get `File Not Found 256` [download] Running `qx(dir thisdoesntexist); print $?>>8;` [download] returns `File Not Found 1` [download] What does it mean to be shifting bits by 8 and how did that change the return code to 1? Thank you, Jason	[reply] [d/l] [select]
Re^2: Return code from calling qx by johna (Monk) on Oct 27, 2009 at 20:06 UTC
Think in terms of binary: `100000000 (binary) = 256 (decimal)` [download] If you shift it 8 bits to the right (>> 8) you get: `1 (binary) = 1 (decimal)` [download] Hope this helps a little. -John	[reply] [d/l] [select]
Re^3: Return code from calling qx by f50bodykit (Initiate) on Oct 27, 2009 at 20:24 UTC
Yes that helps. Thanks John.	[reply]
Re^4: Return code from calling qx by Discipulus (Canon) on Oct 28, 2009 at 10:31 UTC