perl scripting help

[ejm20]

ve been asked to create a perl script in bash that will open an xterm or terminal, cd to a specific directory, the load modules. I have very little perl experience and have been searching the web and books with no luck. I can get it to open the shell with the env/paths but cant execute any commands like a simple "cd". Heres what I got:

#!/usr/bin/perl

system ('gnome-terminal', 'sh', -c 'cd /home/$USER/projects; module lo
+ad project/test' );

Thanks!!!!

Code and p tags added by GrandFather

[kcott]

G'day ejm20,

Welcome to the Monastery.

I'm not entirely sure what your ultimate goal is here. You wrote "create a perl script in bash" which I find confusing. It seems to me that you could put your bash commands in a bash script and run that from an xterm (or equivalent).

Having said that, and based on the code you've managed so far, perhaps you're after something like this:

#!/usr/bin/env perl

use strict;
use warnings;
use autodie ':all';

my @commands = (
    'set -vx',
    "cd $ENV{HOME}",
    'date',
    'pwd',
    '/usr/bin/bash -i',
);

system qw{/usr/bin/xterm -e}, join ';', @commands;

When I run that, it pops up an xterm window containing:

+ cd /home/ken
+ date
Sat, 29 May 2021 10:44:54
+ pwd
/home/ken
+ /usr/bin/bash -i

ken@titan ~
$

I can now type more commands into that xterm window. It shuts down normally with exit or Ctrl-D.

One thing to note is that the Perl script (which I called pm_11133222_xterm.pl) will block until the xterm window closes. If that's an issue, you can run it in the background.

This starts the xterm and returns my normal prompt:

ken@titan ~/tmp
$ ./pm_11133222_xterm.pl &
[1] 2182

ken@titan ~/tmp
$

After closing the xterm and hitting enter:

ken@titan ~/tmp
$
[1]+  Done                    ./pm_11133222_xterm.pl

ken@titan ~/tmp
$

You may, of course, already know how to do that.

I didn't think I had gnome-terminal but apparently I do. I'm running Cygwin 3.2.0 (on Win10) so I no doubt got it via some package. I don't have a manpage for it; I found gnome-terminal(1); it says "gnome-terminal is designed to emulate the xterm program ..." but simply replacing xterm with gnome-terminal resulted in various warning and error messages. I got it to run by replacing the last line of script above with:

system qw{/usr/bin/gnome-terminal -- /usr/bin/bash -c}, join ';', @com
+mands;

This now popped up a window with the same initial content as the xterm window described above; subsequent interaction also worked the same. There were, however, two differences: the Perl script did not block; and, I got this warning:

** (gnome-terminal:2292): WARNING **: Error retrieving accessibility b
+us address: org.freedesktop.DBus.Error.NoReply: Message recipient dis
+connected from message bus without replying

An internet search for that message got quite a few hits. Here's a couple of workarounds to remove the warning:

$ NO_AT_BRIDGE=1 ./pm_11133222_gnome.pl

$ ./pm_11133222_gnome.pl 2> /dev/null

As I don't use gnome-terminal — fairly obviously as I only just found that I had it — I wasn't particularly interested in delving into this further. If you encounter the same problem and identify a genuine fix (as opposed to a workaround) please share as it may be useful to others in the future.

[hippo]

I don't use gnome-terminal but this works for me with xterm. It should get you started, anyway.

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

system ('xterm', '-e', 'ls && sleep 10');

[cavac]

Hmm, if OP wants to have an interactive terminal that just executes some commands before dropping to the command line, something like this should work:

system('xterm', '-e', 'bash -rcfile /home/username/script.sh');

[ejm20]

The xterm does open but closes after the sleep command. How can it stay open? Thanks!!!

[hippo]

The same way you would without using Perl at all. eg:

system ('xterm', '-e', 'ls && read line');

will happily leave the xterm open indefinitely until the user closes it (or submits a line).

[navalned]

Taking it a little further and daemonizing, etc...

#!/usr/bin/env perl
use common::sense;
use POSIX qw//;

defined (my $pid = fork()) or die "Can't fork: $!";
exit if $pid;
chdir "$ENV{HOME}" or die "Can't chdir $ENV{HOME}";
POSIX::setsid or die "setsid: $!";
close STDOUT; close STDIN; close STDERR;
open STDIN, '<', "/dev/null" or die "open: $!";
open STDOUT, '>', "/dev/null" or die "open: $!";
open STDERR, '>', "/dev/null" or die "open: $!";

defined ($pid = fork()) or die "Can't fork: $!";
if ($pid) { waitpid $pid, 0; }
else {
eval { 
my @cmd = (
'/usr/X11R6/bin/xterm',
'-e',
'/bin/sh -c "find . | xargs egrep "perl""', #simulate module loading
);
exec @cmd; 
};
warn $@ if $@;
exit 1;
}

[perlfan]

https://stackoverflow.com/questions/18970135/run-a-shell-command-through-perl-in-a-specific-terminal#18970447