Trying to determine if path exists in environmental variable

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

This code prepends a path to an NT enviromental %PATH%.

Having this code:

#!/usr/bin/perl -w
use strict;

my $Registry;
my $newpath='C:\Perl\bin';
use Win32::TieRegistry ( TiedRef=>\$Registry, Delimiter=>"/", ArrayVal
+ues=>1 );

my $env= $Registry->{"LMachine/System/CurrentControlSet/Control/".
                     "Session Manager/Environment/"}
    or  die "Can't open CCS/SM/Env: $^E\n";
my $path= $env->{"/PATH"}  or die "Can't get PATH: $^E\n";
#Prepend to path

if ($path->[0] =~ /$newpath/ )
{

    print "$newpath is already in your PATH\n";
}
else
{
print "Here\n";    
    $path->[0]= $newpath . "$path->[0]";
    print "Path is now $path->[0]\n";
    $env->{"/PATH"}= $path or die "Can't set PATH: $^E\n"
}
[download]

I know my bug is in the if ($path->[0] =~ /$newpath/ ) statement, but I'm not sure how to fix the bug. How can I search for $newpath without searching for the regular expression $newpath?

Thanks in advance.

Comment on Trying to determine if path exists in environmental variable Download Code

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Re: Trying to determine if path exists in environmental variable by dpuu (Chaplain) on Aug 16, 2002 at 23:13 UTC
I'd try a split and a grep: `my $list = "foo:bar:baz"; my $wanted = "bar"; if (grep {$_ eq $wanted) split ":", $list) { print "found!\n"; }` [download] --Dave	[reply] [d/l]
Re: Trying to determine if path exists in environmental variable by Zaxo (Archbishop) on Aug 16, 2002 at 23:36 UTC
Your $newpath contains regex metacharacters. Change the regex to escape them by: `if ( $path->[0] =~ /\Q$newpath\E/ )` [download] The '\b' in $newpath is interesting, The match /l\bi/ cannot match anything, since '\b' is a zero-width word boundary and 'li' does not contain one :) In a larger issue, the File::Spec module can help with this task. After Compline, Zaxo	[reply] [d/l]
Re: Trying to determine if path exists in environmental variable by tachyon (Chancellor) on Aug 16, 2002 at 23:51 UTC
While the problem occurs in the if() clause the cause is the value of $newpath and the lack of a quotemeta which should be considered mandatory when interpolating a variable into the match side of a regex `my $newpath='C:\Perl\bin'; .... if ($path->[0] =~ /$newpath/ ) # perl sees this as ... =~/C:\Perl\bin/; # you need either to $newpath = quotmeta $newpath # or do it in the match =~/\Q$newpath/` [download] With quotemeta your code runs as expected. cheers tachyon s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print	[reply] [d/l]
Re: Trying to determine if path exists in environmental variable by slojuggler (Beadle) on Aug 17, 2002 at 01:38 UTC
Here's the final code. I implemented Zaxo's suggestion. Thanks to all who helped. Hope you find this code useful! #!/usr/bin/perl -w =pod This script adds paths into the system path. Simply change @newpaths to reflect the directories you'd like to add. Author: P. Rivera Portions inspired by: Marza/Perlmonks, node 156805; Zaxo and various monks, node 190779 =cut use strict; my $Registry; my $newpath; my @newpaths=('P:\Scripts\Admin','P:\Scripts\Anly','P:\Perl\bin'); use Win32::TieRegistry ( TiedRef=>\$Registry, Delimiter=>"/", ArrayVal +ues=>1 ); my $env= $Registry->{"LMachine/System/CurrentControlSet/Control/". "Session Manager/Environment/"} or die "Can't open CCS/SM/Env: $^E\n"; my $path= $env->{"/PATH"} or die "Can't get PATH: $^E\n"; print "Path currently is $path->[0]\n\n"; print "-" x 65 . "\n"; for $newpath (@newpaths) { print "Attempting to prepend $newpath to path.\n\n"; #See if new path is the system PATH if ($path->[0] =~ /\Q$newpath\E/ ) { print "$newpath is already in your system PATH. Not ad +ded again.\n"; } else { $path->[0]= $newpath . ";$path->[0]"; print "Path is now $path->[0]\n\n"; $env->{"/PATH"}= $path or print "Can't set PATH!!: $^E +\n"; } print "-" x 65 . "\n"; } [download]	[reply] [d/l]
(tye)Re: Trying to determine if path exists in environmental variable by tye (Sage) on Aug 17, 2002 at 05:35 UTC
This came up just a couple of days ago, (tye)Re: Setting and changing system variables under win2000. One of our best programmers did this wrong ((tye)Re: How to access system environment variables?) so I wrote CleanPath, which is another example of how to to this. Update: I originally misread your code. Luckily I quickly realized this and then rewrote this node. Now it mostly just links to related nodes. (: - tye (but my friends call me "Tye")	[reply]
Re: Trying to determine if path exists in environmental variable by slojuggler (Beadle) on Aug 16, 2002 at 23:12 UTC
P.S. The if line causes the error: Can't find unicode character property definition via main->e or e.pl at unicode/Is/e.pl line 0 If I change the line to if (1) no error persists, but then the program doesn't do what it's supposed to do. :-)	[reply]