It looks simple: I have a compiled third-party command line program (i.e. no source code available), where I want to catch its output (stdout and stderr). The program is available on Windoze and Unix/Linux, so I'm looking for a portable solution. Should be easy, isn't it? 
$command="bsub $parameters" # 3rd party program
...
$output=qx($command 2>&1); # Works also under Win

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Now consider the case when $parameters happens to be a parameter which bsub doesn't like. For example, the call (on the Win/Unix) command line 
bsub -k

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happens to be illegal because of the -k switch. Not surprisingly, bsub complains: 
bsub: option requires an argument -- k
Usage: bsub ....

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Now to the strange part: If I do the same under Perl, i.e. 
$parameters='-k'
...
$command="bsub $parameters" # 3rd party program
...
$output=qx($command 2>&1); # Works also under Win

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my $output is empty - this happens under Unix and Windows the same. It seems that bsub somehow finds out that its standard error is not connected to a terminal, and then refuses to print the message.

Is my guess likely correct, or are there other possibilities which could explain this behaviour?

And: Is it possible to fool a program (such as bsub) into thinking that it is connected to a terminal, although it is called via backticks from Perl? I guess there is indeed no workaround possible, but just wanted to make sure that I didn't miss something...

Ronald

Ronald Fischer <ynnor@mm.st>

In reply to How to trick this program (weird catch-the-output problem)? by rovf

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