Hi,

Sorry.  I originally posted on comp.lang.perl.misc.  Then someone
encouraged me to post here because it appeared to be a serious
question about how the Win32 port of Perl handles patterns invoving
variables with backslashes.

I was trying to compare Windows paths using patterns in an Active
State Perl 5.6.1 script running on Win2000ProSP3.  It appears to me
that the backslashes in the content of a variable initialed with a
path doesn't work in a pattern.

I created the followed test script in which all four patterns should
match, IMHO.  If the initial content has no backslashes or a pair, the
patterns match.  But the two cases that have a single backslash fail.
Is this a Perl bug or am I in error?

TIA,
Richard

========= Script =============

my $A_B_C = "abc";
$_ = $A_B_C;
print   "\$A_B_C     " .
        (/^$A_B_C$/? "matches" : "does not match") .
        " \"$A_B_C\"\n";            # Matches

my $ABC_DEF = "abc\\def";
$_ = $ABC_DEF;
print   "\$ABC_DEF   " .
        (/^$ABC_DEF$/? "matches" : "does not match") .
        " \"$ABC_DEF\"\n";  # Doesn't match; why?

print   "\${ABC_DEF} " .
        (/^${ABC_DEF}$/? "matches" : "does not match") .
        " \"${ABC_DEF}\"\n"; # Doesn't match; why?

my $ABC_XXX = "abc\\\\def";
print   "\$ABC_XXX   " .
        (/^$ABC_XXX$/? "matches" : "does not match") .
        " \"$ABC_XXX\"\n"; # Matches

=========== Result ==============

$A_B_C     matches "abc"
$ABC_DEF   does not match "abc\def"
${ABC_DEF} does not match "abc\def"
$ABC_XXX   matches "abc\\def"

That is not what is happening.

There is only one round of interpolation on the m//, the string
resulting from the interpolation is further processed by
the regex engine.

There is nothing win32-specific in your problem as far as I can tell.

If you use forward slashes in the paths, then you don't need
to be concerned with backwards slashes at all.  :-)

Forward slashes work fine as the directory separator on Windows.
It is only the _command interpreter_ that demands backwards ones
(because forward ones are used for something else).

You are in error.

If you really need to work with backslashes, then using single quotes
instead of doubles will make your life easier.

The pattern is:  abc\def

The string to match against is:  abc\def

Pattern requires an "a" followed by a "b" followed by a "c"
followed by a digit character...

The string has no digit characters in it, so the match must fail.

You can fix it by calling quotemeta() on $ABC_DEF before doing
the match, or by:

        /^\Q$ABC_DEF\E$/

But disguising a test for equality as a pattern match is
obfuscation, so don't do that in a serious program:

   ( $_ eq $ABC_DEF ? "matches" : "does not match") .

--
    Tad McClellan                          SGML consulting

    Fort Worth, Texas
.

Tad McClellan writes ..

You still regularly need to deal with back slashes when capturing the
output of system commands on Win32 systems.

"demands" might be misleading - you can enclose forward slashes in  
double-quotes to let them skip past the CMD.EXE parser.

--
  Jason King
  To demunge email: strip invalid, ROT13, add com

Right (because the data comes from the command interpreter).

So you do

   tr#\\#/#;

on the paths, then you don't need to be concerned with them once again.

:-)

--
    Tad McClellan                          SGML consulting

    Fort Worth, Texas
.