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Using SprintF in S & R

by dirtdog (Monk)
on Jul 11, 2017 at 17:41 UTC ( #1194845=perlquestion: print w/replies, xml ) Need Help??

dirtdog has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, I'm hoping someone can assist with a one-liner. I'm trying to pad a leading zero to a 5 digit time. I'm close, but I'm missing something.

perl -i.bak -pe 's/\<time\>(\d+)\<\/time\>/\<time\>sprintf("%06d",$1)\ +<\/time\>/ if /\<time\>(\d{5})\<\/time\>/' <file>

I'm ending up with the following:


and I'm expecting this:


any help would be greatly appreciated!

Replies are listed 'Best First'.
Re: Using SprintF in S & R
by herveus (Parson) on Jul 11, 2017 at 18:06 UTC

    The right hand side of s/// does not execute code unless you use the "e" modifier.

    So, s/\<time\>(\d+)\<\/time\>/\<time\>sprintf("%06d",$1)\<\/time\>/e is what you want. Note the "e" after the last slash.

    Edit to correct placement of "e" modifier. Thanks Laurent. Too many slashes and backslashes!

      The right hand side of s/// does not execute code unless you use the "e" modifier.

      Would you bet your money on that statement? I would not.

      You are right, s/// usually does not execute code without the /e modifier. But Perl would not be Perl if you could not mess around with that. Note that even if you could mess with perl, you probably should not.

      I'll abuse a trick invented by Andrew Pimlott, that I saw first in the "Perl hardware store" talks (1, 2, 3, 4) by Dominus:

      #!/usr/bin/perl use strict; use warnings; sub TIEHASH { return bless {},$_[0]; } sub FETCH { return $_[1]; } tie my %X,__PACKAGE__; my $foo='look! no eval: 3735928559'; $foo=~s/(\d+)/$X{sprintf '0x%08X',$1}/; print $foo;
      >perl look! no eval: 0xDEADBEEF >

      But there is also a way without tie magic. Dereferencing an anonymous array reference:

      #!/usr/bin/perl use strict; use warnings; my $foo='look! no eval: 3735928559'; $foo=~s/(\d+)/${[sprintf '0x%08X',$1]}[0]/; print $foo;
      >perl look! no eval: 0xDEADBEEF >

      Both tricks (ab)use the fact that s/// interpolates the replacement expression, unless you force it not to do so (using ' as the delimiter instead of /).


      Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
      I guess you mean to have the "e" modifier at the end of the substitution, not after the regex of the statement modifier (the if conditional).

      Besides, I don't think you need to escape the < and > characters.


        Ack! Thanks for pointing that out. The perils of too much copy and paste.

Re: Using SprintF in S & R
by Anonymous Monk on Jul 11, 2017 at 17:48 UTC
    s{<time>(\d+)</time>}{sprintf "<time>%06d</time>", $1}eg

      thank you! ...worked like a charm.

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