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

I suspect this is a dead-simple Perl newbie question (and I'm a dead-simple Perl newbie! :o) ), but darned if I can work it out. I need to process filenames in the format filename.randomcharsEXT where EXT is a three-letter extension of any case (e.g., gif, Jpg, TXT...) and randomchars is guaranteed not to contain a period or any "special" characters. For an input of filename.randomcharsEXT the output needs to be filename.EXT... in other words, I need to drop the random characters between the dot and the extension. This would be straightforward to do across multiple statements, but I'm thinking I should be able to do it with a single s/// and some thoughtful RE. Darned if I can noodle out the syntax, though. Can anyone point me to some references or examples? Nothing I've found in my search so far has helped. Thanks!

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Re: Drop middle part in a substitution
by Roy Johnson (Monsignor) on Jan 26, 2004 at 18:02 UTC
    s/^(.*\.).*(...)$/$1$2/
    Update:
    No need to fiddle with capturing and replacing. Just strip out the stuff we don't want:
    s/[^.]+(?=...$)//
    The PerlMonk tr/// Advocate
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      "Most magic tricks are easy, once YOU know the secret." -- Marshall Brodien

      Gah! In studying your substitution, it's immediately obvious how it works... but crafting it from scratch was simply beyond me. I guess I just don't "have my head around Perl" yet... but I'll get there eventually, I hope.

      A code snippet that I can just plug in is way more than I was expecting; thank you!

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      Not to be picky but you are aware that newlines are valid in filenames under some OS's, right?

      s/^(\.*\.).*(...)$/$1$2/s;

      [download]

      Of course, two periods within a filename may also throw this off.

      Update: Ok. You all got me. I'm a dipshit. Thanks.

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        s/^(\.*\.).*(...)$/$1$2/s;

        This doesn't work for me:

        $_ = 'filename.12345Gif';
s/^(\.*\.).*(...)$/$1$2/s;
print;

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        Output:

        filename.12345Gif

        Drop that first backslash :)

        s/^(.*\.).*(...)$/$1$2/s;

        dave

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        Two periods should not throw it off: the characters to be discarded were guaranteed not to include any periods, so the greedy match is appropriate.

        As for newlines in filenames: I definitely didn't think of that.

        The PerlMonk tr/// Advocate
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        AFAIK msdos fat is the only filesystem with 8.3 filenames. But fat does not allow a newline (in fact it allows only very few characters, and definitly no control characters but \x7f.)

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        Not to be picky but you are aware that newlines are valid in filenames under some OS's, right? :)

        If the filename ends with a newline, you'll end up keeping the last 4 characters instead of the last three. Try: 

        s/^(.*\.).*(...)\z/$1$2/s;

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        instead.
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Re: Drop middle part in a substitution
by Abigail-II (Bishop) on Jan 26, 2004 at 18:08 UTC
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Re: Drop middle part in a substitution
by borisz (Canon) on Jan 26, 2004 at 18:08 UTC 
      s/[^\.]*(?=(?:jpg|gif|txt)$)//;

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    Boris
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Re: Drop middle part in a substitution
by Not_a_Number (Prior) on Jan 26, 2004 at 18:58 UTC

    TMTOWTDI. Here's a non-regex solution:

    my $name = 'filename.dqhfhqlkGif';
substr $name, (index $name, '.') + 1, -3, '';
print $name;

    [download]

    In fact if you change index to rindex, it'll work even if there's more than one period in the name.

    dave

    Update: Also works with filenames containing newlines.

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