[Perl] chdir and redirection

noir911 · 12-06-2006, 05:24 AM

I wrote this very basic Perl code but it doesn't change the directory nor does it redirect output to the files. Can anyone tell me what I'm doing wrong?

Code:

#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;
my $home="/home/me/coding/";
chdir "$home" or die "cannot change directory: $!";
open STDOUT, ">ls.out" or die "can't write to ls.out: $!";
open STDERR, ">ls.err" or die "can't write to ls.err: $!";
system 'ls -al $home';

chrism01 · 12-06-2006, 05:04 PM

For a start you'll need doublequotes ("), not single quotes (').
Note also that, like bash, it effectively starts a subshell/env, so when it terminates, the calling shell will still be in the orig dir you ran the prog from.
See also: http://perldoc.perl.org/functions/system.html

edit: changed backquotes to double quotes

bigearsbilly · 12-08-2006, 09:38 AM

your code works for me minus the use warnings clause.

Code:

use Env; # enable you to use $HOME

matthewg42 · 12-08-2006, 10:09 AM

At least part of the problem is this line:

Code:

system 'ls -al $home';

Single quotes mean to pass a literal string, but since $home is a variable which you have set in your program, you probably want to have it expanded before it gets passed to ls. Change this line to:

Code:

system "ls -al $home";

By the way, you can get the value of envionrment variables from the %ENV hash. HOME (case sensitive!) is almost always defined in the environment, so you might as well take it from there. For example:

Code:

chdir $ENV{HOME} or die "cannot change directory: $!";

So, all in all, I'd re-write like this:

Code:

#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;

my $dir = $ENV{HOME} . "/coding";

chdir $dir or die "cannot change directory to $dir: $!";
open STDOUT, ">ls.out" or die "can't write to ls.out: $!";
open STDERR, ">ls.err" or die "can't write to ls.err: $!";
system "ls -al $dir";

noir911 · 12-10-2006, 05:42 AM

Matthew, I tried your code on OpenBSD and it doesn't work. It doesn't give any output & just returns me to the shell ($). I am running it from /home/me.

matthewg42 · 12-10-2006, 06:08 PM

What do you get when you execute these commands from the shell:

Code:

echo "shell is $SHELL"
echo "home is $HOME"
which perl
perl --version