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

Assume you've got the following code:

#!/usr/bin/perl -w

$ID="1234";

open(FILE,"<file.txt");
while(<FILE>) {
    print;
close(FILE);

exit 0;

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And the file "file.txt" contains:

This is a text file. My ID number is $ID.

When printing out that line, it prints out '$ID' instead of evaluating the variable. How to get the variable to be evaluated? This is eluding me for some reason.

Replies are listed 'Best First'.
Re: Eval'ed data loaded from a file?
by chromatic (Archbishop) on Dec 28, 2000 at 01:46 UTC
    There are at three options. First, write a regex that scans your text for variables, replacing them with the values. It's much, much easier to use a hash for this: 
    my $text = "Insert $id here!\n";
my %values = ( id => 10 );
$text =~ s/\$(\w+)\b/$values{$1}/g;
print $text, "\n";

    [download]
    That's untested, but can't be too far off. This is a simple solution that works for simple problems. It's possible to craft a much nicer regex to catch boundary conditions, but it's difficult.

    The second option is an awful abuse of eval I like to call Double Interpolation of a String . I wouldn't recommend it, if you can avoid it.

    The third option is to use a templating mechanism from the CPAN, like Text::Interpolate or Text::Template. This is by far the most powerful and safe mechanism. If you're going to be doing this often, time invested in learning one of these modules will pay off nicely.

[reply]
[d/l]
      Much abliged.

      I was hoping that there was some stupidly simple explaination but I was expecting something like the above.

      Again, thanks for your time.

[reply]
Re: Eval'ed data loaded from a file?
by chipmunk (Parson) on Dec 28, 2000 at 01:48 UTC
[reply]

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