What does =~ do in Perl?

=~ is the operator testing a regular expression match. The expression /9eaf/ is a regular expression (the slashes // are delimiters, the 9eaf is the actual regular expression). In words, the test is saying “If the variable $tag matches the regular expression /9eaf/ …” and this match occurs if the string stored in $tag contains those characters 9eaf consecutively, in order, at any point. So this will be true for the strings

9eaf

xyz9eaf

9eafxyz

xyz9eafxyz

and many others, but not the strings

9eaxxx
9xexaxfx

and many others. Look up the ‘perlre’ man page for more information on regular expressions, or google “perl regular expression”.

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