Your issue is that '?' is a control character in regular expressions - it means match zero or one of the preceding character/pattern. You need to escape the '?' to get a literal '?', i.e.:

$temp1='http://test.com/web/main\?';
$temp2='https://test.com/web1/test1'; 
$proc_string =~ s/$temp1/$temp2/g;
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See Regular Expressions, in particular the section on quantifiers, for details.