[Chicago-talk] trouble caputuring return value

Shlomi Fish shlomif at iglu.org.il
Wed Mar 31 06:13:27 PDT 2010

Hi Richard!

On Wednesday 31 Mar 2010 15:37:16 Richard Reina wrote:
> I have a program that opens a separate terminal and prompts the user for
> some information.  However, for some reason I can't seem to capture the
> return value.  Does anyone happen to know why the value returned by
> get_info.pl is not getting returned? Any help would really be appreciated.
> Thanks
> Richard
> #!/usr/bin/perl -w
> use strict;
> my $info;
> system(q{gnome-terminal --geometry=80x12-0-30 -x perl -e 'require
> "./get_info.pl"; ($info) = get_input();'});

You should not expect Perl to assign to a variable in the main program by 
evaluating an assignment to its name in a different process. To communicate 
with a child process you need inter-process communications, such as anonymous 
pipes, sockets, named pipes, System V IPC, mmap, using the file-system for 
that, etc. Please read a little about UNIX multi-processing basics (a lot of 
which is also relevant to Windows and other operating systems). 

> print $info . "\n";
> <<<<<<< get_info.pl >>>>>>>>
> #!/usr/bin/perl -w
> use strict;
> print "Enter Info\n";
> chomp (my $info = <STDIN>);
> return $info;

You cannot use return to return an arbitrary Perl value from a program. It 
only works for functions. As far as C and UNIX are concerned, everything that 
comes out of a process must be in sequences of octets. You need to use 
"print()" on something to emit it to the outside somehow.


	Shlomi Fish

Shlomi Fish       http://www.shlomifish.org/
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