Did you escape the $1 in the value? Also, you will need to double evaluate, and fix what you are evaluating:
my %patt1;
my $key = "<date>([A-Z&;][a-z&;]+), ([0-9]{2}) ([0-9]{4})</date>";
my $value = "qq|<month>\$1</month>|";
$patt1{$key} = $value;

$instr = '<date>Jan, 10 1997</date>';
for my $pat (keys %patt1)
{
    if ( $instr =~ s|$pat|$patt1{$pat}|eegs ) {
      print "match1: $instr\n";
    }
}

[download]
If you're doing this repeatedly in your program, though, it would be better to compile the regexes with qr and store them in an array rather than as keys in a hash.

In reply to Re: interpolation in replacement part by runrig
in thread interpolation in replacement part by anniyan

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.