2

This code outputs the scalars in the row array properly:

  $line = "This is my favorite test";
  @row = split(/ /, $line);

  print $row[0];
  print $row[1];

The same code inside a foreach loop doesn't print any scalar values:

  foreach $line (@lines){
      @row = split(/ /, $line);
      print $row[0];
      print $row[1];
  }

What could cause this to happen?

I am new to Perl coming from python. I need to learn Perl for my new position.

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  • 5
    Your code works fine for me. Are you sure that @lines is properly initialized? (Also, maybe you're declaring variables elsewhere, but these snippets would fail to run with use strict;) Commented May 7, 2010 at 17:28
  • When you write split / / ... or split /\s+/ ..., it's almost always better to use split " " ... instead. perldoc.perl.org/functions/split.html Commented May 7, 2010 at 17:51
  • Note that in Perl the print builtin takes a list as an argument, and slices are possible as well, so you could simplify your code by writing print @row[0..1] or print @row[0,1]. Doing print ...; print ...; is ok but I wouldn't recommend it. Commented May 7, 2010 at 17:56
  • See perldoc print for full information on it. (In fact, I recommend using perldoc every time you encounter something new, it answers tons of newbie questions right off the bat.) Commented May 7, 2010 at 17:57
  • 3
    You may get helpful error messages if you use use strict; use warnings;, which should be used in every perl script and module. Commented May 7, 2010 at 18:21

2 Answers 2

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3

As already mentioned in Jefromi's comments, whatever the problem is, it exists outside of the code you posted. This works entirely fine:

$lines[0] = "This is my favorite test";

foreach $line (@lines) {
    @row = split(/ /, $line);
    print $row[0];
    print $row[1];
}

The output is Thisis

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1

When I run into these sorts of problems where I wonder why something in a block is not happening, I add some debugging code to ensure I actually enter the block:

 print "\@lines has " . @lines . " elements to process\n";
 foreach my $line ( @lines )
      {
      print "Processing [$line]\n";
      ...;
      }

You can also do this in your favorite debugger by setting breakpoints and inspecting variables, but that's a bit too much work for me. :)

If you need to learn Perl and already know Python, you shouldn't have that much trouble going through Learning Perl in a couple of days.

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