The /r modifier for the tr/// and s/// operators has been added in version 5.14, see the perl 5.14 delta

Edit: you don't need it though, without /r $string =~ s/search/rep/; will apply its modifications directly on $string. The /r modifier is used to keep the original string intact and output the result to another one.

In reply to Re: problem with perl 5 by Eily
in thread problem with regex in perl script intended for 5.20,but while running on 5.10 by praveenchappa

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