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

Dear monks: I have a text file which contains:

The variable is $var_one.

I think the following program should copy it to STDOUT, and expand variable names found in the file, but it causes an "uninitialized variable" error in the evaluation: 
my $var_one;
sub copy_file {
  open(IFILE, "<afile");
  while($x = <IFILE>) {$x =~ s|(\$\w+)|$1|eeg; print $x};
  close(IFILE);
}

copy_file();

[download]
This works, by bringing the variable inside the sub: 
my $var_one;
sub copy_file {
  my $var_one = $var_one;
  open(IFILE, "<afile");
  while($x = <IFILE>) {$x =~ s|(\$\w+)|$1|eeg; print $x};
  close(IFILE);
}

[download]
This works too, and finds the global variable: 
my $var_one;
sub copy_file {
  my $x = "<p>The variable is $var_one.</p>";
  $x =~ s|(\$\w+)|$1|eeg; print $x;
}

[download]
If I evaluate only once, I get the name of the variable, from the file, as expected: 
sub copy_file {
  open(IFILE, "<afile");
  while($x = <IFILE>) {$x =~ s|(\$\w+)|$1|eg; print $x};
  close(IFILE);
}

[download]
So... the expression s|(\$\w+)|$1|eeg fails only when the variable is outside the sub, and only when called from inside the while statement. How can I force the RE to find the global variable?

Replies are listed 'Best First'.
Re: about scope and s///eeg
by shenme (Priest) on Sep 12, 2003 at 07:36 UTC
    Your example as given is perhaps not what you're really running?   Fixing the example is as simple as adding 
        $var_one = 'now defined';

    [download]
    after the my $var_one;.
[reply]
[d/l]
      Oops. The global variable is really initialized when defined, as in: 
      my $var_one = "a string";

sub copy_file {
  my $f = shift;
  open(IFILE, "<$f");
  while($x = <IFILE>) {$x =~ s|(\$\w+)|$1|eeg; print $x};
  close(IFILE);
}

copy_file("afile");

      [download]
[reply]
[d/l]
        But then you still get warnings?   What I tested with was: 
        #!/usr/bin/perl -w

use strict;
use warnings;

my  $var_one;
    $var_one = 'now defined';

sub copy_file {
  while( my $x = <DATA>) {
      $x =~ s|(\$\w+)|$1|eeg; 
      print $x;
  };
}

copy_file();

__DATA__
The variable is $var_one.

        [download]
        As coded above I get the output 
        The variable is now defined.
        If I comment out the   $var_one =   I see 
        Use of uninitialized value in substitution iterator at anon02.pl line 12, <DATA> line 1.
The variable is .
        Any chance the variable name is misspelled in the text file?   When I tried the following data: 
        __DATA__
The variable is $var_one.
The variable is $var_one2.
The variable is $Var_one.
        I got error messages: 
        The variable is now defined.
Use of uninitialized value in substitution iterator at anon02.pl line 14, <DATA> line 2.
The variable is .
Use of uninitialized value in substitution iterator at anon02.pl line 14, <DATA> line 3.
The variable is .
[reply]
[d/l]

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