Running a backticks command in a CGI script

[Cody Fendant]

I have a command foobar which runs just fine from the command line as a normal user.

When I run foobar it normally takes about 5 seconds, then returns "success".

I want to run the command in a CGI script and print the "success" text back to the browser.

If I put $result = `foobar` into my CGI script, it finishes instantly (no 5-second wait) and $result is empty.

How do I troubleshoot this? If the script couldn't find foobar in the path, I would at least get something like "unknown command" back, right?

So the command is silently failing, perhaps because of permissions, because it's running as the www username? What can I do to figure out what's happening and how to get it to work?

[NetWallah]

Try capturing STDERR in addtion to the STDOUT output:

 $result = `foobar 2>&1`

You should also check the value of "$?". From the docs:
$? may be set to non-0 value if the external program fails. The upper eight bits reflect specific error conditions encountered by the program (the program's "exit()" value).

[Cody Fendant]

That's done the trick, thank you. I have a full, detailed and ... incomprehensible error message now. But that's cool, I've solved the immediate problem.

[kcott]

G'day Cody Fendant,

Yes, I can make that silently fail too:

$ perl -e '$result = `foobar`'

But I start getting feedback if I ask for it (i.e. with strict and warnings):

$ perl -Mstrict -Mwarnings -e '$result = `foobar`'
Global symbol "$result" requires explicit package name at -e line 1.
Execution of -e aborted due to compilation errors.

OK, let's fix up that one from strict:

$ perl -Mstrict -Mwarnings -e 'my $result = `foobar`'
Can't exec "foobar": No such file or directory at -e line 1.

Now this one from warnings which clears all errors:

$ perl -Mstrict -Mwarnings -e 'my $result = `ls`'

Given you're working in a CGI environment, you may find the fatalsToBrowser feature of CGI::Carp to be useful.