Yes, perl interpolates double quoted strings, including regular expression patterns used in the match and substitution operators.    The gory details are in: Gory details of parsing quoted constructs.

If you don't want string interpolation you can use single quoted operators: 

if ( $hello =~ m'^[ \|\t\r\n]+$' ) {

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But then "\t", "\r" and "\n" won't be interpolated.

In reply to Re: left side of pattern matching by jwkrahn
in thread left side of pattern matching by BeneSphinx

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