Re: How to handle input and output of a program executed by System function in perl

510046470588-0001_at_t-online.de
Date: 07/20/04 

Date: 20 Jul 2004 08:50:48 +0200

zw@cs.man.ac.uk (zw) writes:
>
> Hi,
> I think Perl is good at dealing with system functions like other
> scripting languages do. But I am not sure how does it handle inputs
> and outputs from
> external programs? for example,
> system "java Foo arg1 arg2";
> Can I assign the result returned by Foo.java to a variable like
> $a = system "java Foo arg1 arg2";

the simplest way is
$a = `java Foo arg1 arg2`;

another example is
$s = `cat filename`;
for retrieving the content of an external file, when cat is the
unix command.

in array context, this approach splits the output string into lines.

a safer way would use the functions fork, exec, and pipe for starting
the external programm and indirecting its output into a file handle.

if the program reads or writes (but not both) continually from Stdin/out,
the open function may be used with a pipe.

bidirectional communication, as needed when e.g. writing a perltk interface
to a command line interpreter like octave, is more difficult,
as it has deadlocks coming if not handled carefully.
IPC::Open2 may help, or IO::Pty ;

Klaus Schilling

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