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mohanm_eee has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

I have a text file as below and saved it as "file.txt"

"create variable $VAR alarm_object 0"

Iam trying to read this in a perl script and printing it by substituting the "$VAR" variable

$VAR = TEMP_VAR
open (FILE,"<", "file.txt") or die $!;
        while (<FILE>) {
                chomp;
                eval(print "$_\n");
        }
        close (FILE);

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I want the output as

"create variable TEMP_VAR alarm_object 0"

I tried to achieve this using eval function. It is not working as expected.

How can i achieve this in perl?

Replies are listed 'Best First'.
Re: Substituting Variables while reading text file
by toolic (Bishop) on Aug 05, 2014 at 18:04 UTC
    s/// 
    use warnings;
use strict;

my $VAR = 'TEMP_VAR';
while (<DATA>) {
    s/\$VAR\b/$VAR/g;
    print;
}

__DATA__
create variable $VAR alarm_object 0

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Re: Substituting Variables while reading text file
by frozenwithjoy (Priest) on Aug 05, 2014 at 18:05 UTC

    Edit: Oops, toolic beat me to the punch!

    What about something like this: 
    #!/usr/bin/env perl
use strict;
use warnings;

my $VAR = "TEMP_VAR";

while (<DATA>) {
    s/\$VAR/$VAR/;
    print;
}

__DATA__
create variable $VAR alarm_object 0

    [download]
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Re: Substituting Variables while reading text file
by Laurent_R (Canon) on Aug 05, 2014 at 18:52 UTC
    The problem is probably that you are using a bare word instead of a string. Try changing: 
    $VAR = TEMP_VAR

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    to 
    my $VAR = "TEMP_VAR";

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    and it should work. My quick test with a Perl one-liner under Unix: 
    $ echo 'create variable $VAR alarm_object 0' | perl -e '$VAR = "TEMP_V
+AR"; while (<>) { chomp; eval (qq{print  "$_\n";});}'
create variable TEMP_VAR alarm_object 0

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    My understanding is that this is closer to what the OP wanted than s///, but I may of course be wrong.
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Re: Substituting Variables while reading text file
by aitap (Curate) on Aug 07, 2014 at 07:21 UTC

    String::Interpolate might be useful in this task. If you move your variables to be interpolated to a hash, you will be able to do it yourself, like this: 

    my %variables = ( ... );
...;
while (<FILE>) {
 s/\$(\w+)/$variables{$1}/eg;
 print;
}

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    (untested).

    What you are writing looks like a templating engine. Unless it's a "homework" question, it might be useful to look at Text::Template, Mason and Template.

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