Dear Monks,

I'm wondering if anyone can suggest an elegant solution to my regex substitution question. In the following: 

my $greekReplace = "alpha|beta|chi|delta|epsilon|eta|gamma|hbar|kappa|
+lambda|mu|nu|omega|phi|pi|psi|rho|sigma|tau|theta";
my $string = '3*mu';
$string =~ s/($greekReplace)/\\$1 /isg;

[download]
$string would end up as '3*\mu ' (note trailing space). This all works fine.

The issue is that I need to be able to NOT do the 'mu' substitution when 'mu' is prepended with 'a', as in 'amu'.

While I'm sure I can figure out a clunky way of doing the substitution with multiple levels of parentheses and memory variables, I'm wondering if there is a simple solution. I tried using 'a{0}mu' in the above string, but that doesn't work.

Here is some code I have used to test things I've tried:

#!/usr/bin/perl

use strict;
use warnings;

my $greekReplace = "alpha|beta|chi|delta|epsilon|eta|gamma|hbar|kappa|
+lambda|mu|nu|omega|phi|pi|psi|rho|sigma|tau|theta";

my %strings = ( 
    mu  => { valid => '\mu ' },
    amu => { valid => 'amu' },
    bmu => { valid => 'b\mu ' },
    cmu => { valid => 'c\mu ' },
    mud => { valid => '\mu d' },
    '3*mu' => { valid => '3*\mu ' },
);

foreach my $string (sort keys %strings) {
    print "Before: '$string'; ";
    my $string2 = $string;
    $string2 =~ s/($greekReplace)/\\$1 /isg;
    print "After: '$string2' ; Should be: $strings{$string}->{valid}; 
+";
    print $string2 eq $strings{$string}->{valid} ? "Passes\n" : "FAILS
+\n";
}
print "\n";

[download]

Thanks

Update: Thanks Monks....the negative look-behind does the trick!

In reply to Regex question by memnoch

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