You don't have to escape the \\ if you
don't put it into ".."'quotes (except \'), just by removing
the escapes, your code will work fine,
<workable example provided>:
use strict;
use warnings;

my $text=q'
\Start
We have $\alpha$-helical to a $\beta$-sheet proteins and stuff.
The $\beta$-sheet structures relate to $\pi$ by several \degrees.
';

 my %allowed_text_code = (
 '$\alpha$'  => '&#945;',  '$\beta$'   => '&#946;',
 '$\gamma$'  => '&#947;',  '$\delta$'  => '&#948;',  
 '$\theta$'  => '&#952;',  '$\pi$'     => '&#960;',
 '\degrees'  => '&#176;' );

 foreach my $tex_key (keys %allowed_text_code) {
    $text =~ s/\Q$tex_key\E/$allowed_text_code{$tex_key}/g;
 }
 print $text. "\n";

[download]

This would not hold if your TeX-Source don't
look like I expected ;-)

Regards
mwa

In reply to Re: character encoding ambiguities when performing regexps with html entities by mwah
in thread character encoding ambiguities when performing regexps with html entities by angelixd

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