source vaibale in perl

bharatbsharma · 04-27-2010, 11:10 PM

Hello

I can define all variables in tcl programming in a file for instance var.cfg
and source the same file in my tcl script such as

source var.cfg

Is this possible in perl too?

smoker · 04-28-2010, 01:17 AM

you can use

require "filename.pl"

or

require "filename.txt"

filename.txt (or .pl) doesn't need #!/usr/bin/perl at the start, but the file must end with

1;

on it's own.

bigearsbilly · 04-28-2010, 03:33 AM

Quote:

Originally Posted by smoker

but the file must end with

1;

on it's own.

that is not strictly correct. the last statement must return a true value.

here is a (hastily written) example of how to save a hash to file and read it in
on the next invocation. The sort of thing that's easy in tcl and lisp.
if you try it the 'now' should change on each go.

(ignore the hard-coded file names, bad style)

Code:

use strict;
use warnings;
use Data::Dumper;

our %thing;

require "./1" if -f "./1";
%thing = (
        fish => 'lips',
        create => scalar localtime(),
        ) unless %thing;

$thing{now} = scalar localtime;

open OUT, ">1" or die "ouch! $@\n";
print OUT  Data::Dumper->Dump ( [\%thing], [qw(*thing)]) ;
print Data::Dumper->Dump ( [\%thing], [qw(*thing)]) ;

Sergei Steshenko · 04-28-2010, 07:02 AM

Quote:

Originally Posted by bharatbsharma

Hello

I can define all variables in tcl programming in a file for instance var.cfg
and source the same file in my tcl script such as

source var.cfg

Is this possible in perl too?

Well, YES and NO. The YES part is that you can get values of variable from an external file provided the variables are global/package ones.

The NO part is that you can't get value of lexical variable through 'require', but you can through 'eval'.

A better idiom is to import an anonymous hash:

Code:

sergei@amdam2:~/junk> cat -n hash_importer.pl
     1  #!/usr/bin/perl -w
     2
     3  use strict;
     4
     5  my $x = 10;
     6  my $hash_ref = require './hash_to_be_imported.prl';
     7
     8  warn "\$x=$x";
     9
    10  foreach my $key(keys %{$hash_ref})
    11    {
    12    warn "key/value: $key/$hash_ref->{$key}"
    13    }
sergei@amdam2:~/junk> cat -n hash_to_be_imported.prl
     1  {
     2  foo => 1,
     3  bar => 2
     4  }
sergei@amdam2:~/junk> ./hash_importer.pl
$x=10 at ./hash_importer.pl line 8.
key/value: bar/2 at ./hash_importer.pl line 12.
key/value: foo/1 at ./hash_importer.pl line 12.
sergei@amdam2:~/junk>

If you want to delve deeper into the issue and understand how Perl uses lexical scoping to isolate things, replace contents of 'hash_to_be_imported.prl' file with these:

Code:

sergei@amdam2:~/junk> cat -n hash_to_be_imported_1.prl
     1  my $x = 0;
     2
     3  warn "IMPORTED FILE: \$x=$x";
     4
     5  {
     6  foo => $x++,
     7  bar => $x++
     8  }
     9
sergei@amdam2:~/junk>

and look carefully at the behavior/value of $x in both files.

The point of my example is complete separation of the data to be imported from the importer - this allows a lot of reuse of the data to be imported. Another point is that data to be imported can not screw up the importer provided the importer is written using only lexical variables.