Basic regex syntax, brackets create a character class 
use re 'debug';
my $orig = 'my_stuff[1]=400';
my $want = 'my_stuff[1]=';


print "They Match\n" if  $orig =~ /$want/;
__END__
Compiling REx "my_stuff[1]="
Final program:
   1: EXACT <my_stuff1=> (8)
   8: END (0)
anchored "my_stuff1=" at 0 (checking anchored isall) minlen 10
Guessing start of match in sv for REx "my_stuff[1]=" against "my_stuff
+[1]=400"
Did not find anchored substr "my_stuff1="...
Match rejected by optimizer
Freeing REx: "my_stuff[1]="

[download]
you want /\Q$want\E/ or substr

In reply to Re: How does this regex not match? by Anonymous Monk
in thread How does this regex not match? by Anonymous Monk

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