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Re^2: Regular Expressions: Removing 'only' single spaces from a string

by BioBoy (Novice)
on Oct 20, 2005 at 23:37 UTC ( [id://501847]=note: print w/replies, xml ) Need Help??


in reply to Re: Regular Expressions: Removing 'only' single spaces from a string
in thread Regular Expressions: Removing 'only' single spaces from a string

This solution worked perfectly. Now, do you think you could break it down for me? Forgive me, but I'm having a little trouble understanding it.

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Re^3: Regular Expressions: Removing 'only' single spaces from a string
by GrandFather (Saint) on Oct 20, 2005 at 23:54 UTC

    Did it though? Consider:

    use warnings; use strict; my $str1= "It is very very cold now\n"; my $str2 = $str1; $str1 =~ s/(?<! ) (?! )//g; print $str1; $str2 =~ s/ (?! )//g; print $str2;

    which prints:

    Itisvery verycoldnow Itisvery verycoldnow

    Which string is correct? The (?<! ) is a zero width look back negative assertion: it matches if there isn't a space before the current space being matched. The (?! ) is a zero width look ahead negative assertion: it matches if there isn't a space after the current space being matched. Together these ensure that only single spaces are matched: only match a space that doesn't have a space before it and doesn't have a space after it.

    You should have a look at perlretut.


    Perl is Huffman encoded by design.
      Thanks for that explaination.

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