Did you read error indicators? Essentially (as gwadej and toolic as also pointed out) you are not checking the error code you think you are. $! is set by the perl C libraries, not by external system calls, and its value is essentially meaningless unless a Perl library call (like open) just failed. On the other hand $? is set to the return value of the invoked system call, and as such is what you need to check in the case of backticks (or system). | [reply] |
Yes, I realize now that I'm not doing my error checking correctly by using $! but my next question (read: obsession) is why do the perl C libraries set errno to "Bad file descriptor" whenever perl executes a shell command using backquotes that sends data to STDOUT?
Consider this:
perl -e '$res = `echo test`; print $!."\n";'
versus this:
perl -e '$res = `echo test>/dev/null`; print $!."\n";'
In the first example, $! is "Bad file descriptor". In the latter example, $! is empty. So whatever the answer is, it has something to do with whether or not the command has output. You can replace "echo test" with any shell command that produces STDOUT info.
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Try using strace to find out.
Nevermind, I just did, and I don't see a system call returning that error.
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Not entirely sure, but an interesting test case I found is the following:
perl -e 'print `echo test`; print $!."\n";'
shows $! to be empty. I am guessing the issue is that echo is attempting to output to a non-existent terminal, and this error is a result of an internal perl call to determine if the output is being piped to an existing terminal. Note that perl -e 'print $res = `echo test`; print $!."\n";'
does yield $! eq "Bad file descriptor".
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