I have come across a regex while debugging some code and while I have understood part of it , i need to understand entirely in order to accommodate new changes in requirement.

$inp =~ s/<%([^=].*?)%>/eval $1/ges  #this is one 
$inp =~ s/<%=(.*?)%>/eval $1/ges  #this is the second

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Now when i have 2 input strings one : 

<%
my $test='';
if (@{$ctxt{'params'}})
{
$test=
'index=1011'
'asln=' . join(' ',@{$ctxt{'params'}})."\n".
}
$test;
%>

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second input string 

<% $ctxt{'common_params'}; %>

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My understanding of the above regex is when it encounters "<%" it substitutes the value of the variable eg: it assigns test variable with value index and asln , but i fail to understand what is eval doing here ? and what about $1 ? can anyone explain me ?

In reply to regex understanding help by t-rex

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