You can use the eval function to substitute a value defined by a variable. Suppose you have a string literal $a = 'a $string' and you want Perl to substitute $string with the value of the $string variable. This is normally not a problem. Because if you use double quote, Perl does the interpretation automatically: $string = 'theactual'; $a = "a $string"; pri... But this doesn't work if the value of $string isn't available when you define the template $a . In this case, you have to use single quote to preserve the template definition. But you can use eval to do the replacement when the value of $string becomes available: #!/usr/bin/perl $a = 'a $string'; $string = ...

Variable Meaning $_ The default or implicit variable. @_ Within a subroutine the array @_ contains the parameters passed to that subroutine. $a, $b Special package variables when using sort() $<digit> Contains the subpattern from the corresponding set of capturing parentheses from the last pattern match, not counting patterns matched in nested blocks that have been exited already. $. Current line number for the last filehandle accessed. $/ The input record separator, newline by default. $| If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel. Default is 0 (regardless of whether the channel is really buffered by the system or not; $| tells you only whether you've asked Perl explicitly to flush after...