IPC::Open2

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

I need to execute a program, write some data to its stdin and then read its stdout. A little research has yieled that open FILE, "| $prog |"; does not work for some less than obvious reasons.

Gladly, perl comes with IPC::Open2, which allows you to direct the STDIN and STDOUT of an executed program and let your script control them. But, for some reason my code isn't working. Here is is:

#!/usr/bin/perl
use IPC::Open2;

print open2(\*BOIN, \*BOOUT, "cat"); 

print BOIN "proclist\n";
print BOIN "quit\n";
close BOIN;

while (<BOOUT>) {
    print;
}
close BOOUT;
[download]

Prints nothing. Any thoughts?

Comment on IPC::Open2 Select or Download Code

Replies are listed 'Best First'.
Re: IPC::Open2 by btrott (Parson) on May 19, 2000 at 21:48 UTC
Because you've switched BOIN and BOOUT. You need to write to BOOUT and read from BOIN--you were doing the opposite. It should read: `#!/usr/bin/perl -w use strict; use IPC::Open2; print open2(\BOIN, \BOOUT, "cat"); print BOOUT "proclist\n"; print BOOUT "quit\n"; close BOOUT; while (<BOIN>) { print; } close BOIN;` [download] If you'd had warnings on in your original, you would have received this warning: `Filehandle main::BOIN opened only for input at foo.pl line 8. Filehandle main::BOIN opened only for input at foo.pl line 9.` [download] By the way, as perlipc warns, watch out for Unix buffering. In this case (using cat) you might want to use the -u flag for unbuffered output. In your case, it doesn't matter much, since you close the output filehandle. But in general, it's something to think about.	[reply] [d/l] [select]
Re: IPC::Open2 by pschoonveld (Pilgrim) on May 19, 2000 at 21:53 UTC
Damn, I'm stupid. RTFM for me. Thanks.	[reply]


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