To understand how single and double quotes work in Perl, maybe perlop helps you.

The problem at hand is really simple, and had you used strict, Perl would have told you about your usage of $dfull and $full.

I recommend to also print out the value you are actually checking with the -X test as follows:

my $dir= $part1;
if( -e $dir ) {
    print "-e $dir is true\n"
} else {
    print "-e $dir is false\n"
};
[download]

That way, you will see what expressions you actually check, and you'll find out that $path is empty, as $dpath contains the value you've constructed.

G'day LloydRice,

You appear to have answers to your questions from various monks.

Seeing the amount of code you wrote for your tests, I thought I'd introduce you to the built-in module Test::More.

I don't have Perl running on an MSWin platform (so I can't duplicate your exact tests) but the following should give you an idea of how much coding this module can save you. I also think that, with the substantially reduced code, the tests themselves become far more obvious and the code is more readable and maintainable.

#!/usr/bin/env perl

use strict;
use warnings;

use Test::More tests => 3;

ok(-e '/Users/ken/tmp/Sample Music', 'Single quotes');
ok(-e "/Users/ken/tmp/Sample Music", 'Double quotes');
ok(-e "'/Users/ken/tmp/Sample Music'", 'Single quotes in double quotes
+');
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Output:

1..3
ok 1 - Single quotes
ok 2 - Double quotes
not ok 3 - Single quotes in double quotes
#   Failed test 'Single quotes in double quotes'
#   at ./pm_example.pl line 10.
# Looks like you failed 1 test of 3.
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Thanks to all who weighed in on this. I have learned a lot. Judging by the tone of many of the replies, some will be glad to hear that I have started using "strict" (at least some of the time).

However, it turns out that the real problem was that I was mixing Perl functions for file operations with Win command lines executed via qx. What I had not considered (and learned) was that qx actions go through the Win command line interpreter, but the Perl functions, in particular, the -x tests, do not. The difference is, of course, that path/file names with spaces get chopped up by the CLI and thus required enclosing Dquotes, but work fine in the -x tests, in which case, the Dquotes mess things up.

I am now using the Perl file operations in Win32::File and Win32::CopyFile and nearly everything is working. A little more clean-up and the job will be done.

Again, thanks for all the help.

Lloyd.

I then tried the File::Spec module. It helps.

$me = "dirtest3";

# Perl script to test variations on file/dir test argument quoting

use File::Spec;

print "All of the following conditions are true on my system.\n";
print "The issue is to see which tests work.\n";
print "The final path includes a directory name containing a space.\n"
+;
print "\n";


$part1 = "C:";
$part2 = "users";
$part3 = "public";
$part4 = "Music";
$part5 = "Sample Music";
$full = File::Spec->catfile( $part1, $part2, $part3, $part4, $part5 );

print "\nThese tests use a path consisting of concatenated substrings:
+\n";
print "  full = '$full'\n";
print "\n";


$expl = "Full path, unquoted";
if ( -e $full )
{ print "'-e $expl' is true\n"; } else { print "'-e $expl' is false\n"
+; }

$expl = "Full path in single quotes";
if ( -e '$full' )
{ print "'-e $expl' is true\n"; } else { print "'-e $expl' is false\n"
+; }

$expl = "Full path in double quotes";
if ( -e "$full" )
{ print "'-e $expl' is true\n"; } else { print "'-e $expl' is false\n"
+; }
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All of the following conditions are true on my system.
The issue is to see which tests work.
The final path includes a directory name containing a space.


These tests use a path consisting of concatenated substrings:
  full = 'C:\users\public\Music\Sample Music'

'-e Full path, unquoted' is true
'-e Full path in single quotes' is false
'-e Full path in double quotes' is true
[download]

OK. Finally. Here's my real question.

What's the difference between the strings $dfull in test2 and $full in test 3? I know that $full did not print correctly in test3 because it was single quoted in the print statement. But that is really part of my question. What is different about a string that parses correctly with or without single quotes. I understand that double quotes trigger interpolation. But single quotes don't do that. What do they do?

What's the difference between the strings $dfull in test2 and $full in test 3?

Just to retrace your steps a bit, do you understand the difference between  $dfull in dirtest2 and  $full also in dirtest2? Had strictures (see strict) been enabled, Perl would have refused to compile  $full because it was not pre-defined. Without strictures but with warnings enabled, Perl would have told you that  $full was undefined wherever you used it in this state. These two pragmata can be enormously useful to the learning (and even the experienced) programmer. A word to the wise...

And certainly do study and understand the difference between interpolating (double-quotish) and non-interpolating (single-quotish) string operators.

See perlop: Quote and Quote like operators. Understanding Perl's string handling generally and the different quote types particularly is fundamental to making good use of Perl.

If the code changes take longer than the time saved, it's fast enough already.

Thanks, Corion. I will reread perlop and study these cases some more.