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in reply to How to replace Tab with spaces not altering postion

> perldoc -q tabs
Found in /usr/local/lib/perl5/5.6.1/pod/perlfaq4.pod
  How do I expand tabs in a string?

      You can do it yourself:

  1 while $string =~ s/\t+/' ' x (length($&) * 8 - length($`) % 8)/e;

      Or you can just use the Text::Tabs module (part of the standard 
+perl distribution).

  use Text::Tabs;
  @expanded_lines = expand(@lines_with_tabs);

>

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and this from perlop:
   Occasionally, you can't use just a `/g' to get all the changes to
   occur that you might want.  Here are two common cases:

      # put commas in the right places in an integer
      1 while s/(\d)(\d\d\d)(?!\d)/$1,$2/g;

      # expand tabs to 8-column spacing
      1 while s/\t+/' ' x (length($&)*8 - length($`)%8)/e;

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And this has been in the perl man page since perl1!

    print "\et" x ($tab/8), ' ' x ($tab%8);    # tab over

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  p

Replies are listed 'Best First'.
Re^2: How to replace Tab with spaces not altering postion
by Aristotle (Chancellor) on Oct 11, 2002 at 21:45 UTC

    The problem is it's using $` which incurs a huge performance penalty.

    Here's another OWTDI:

    $_ = join "", map { $_ . " " x (8 - length() % 8) } split /\t/, $_, -1; Update: blakem points out that this code is broken. It will pad all parts of the string to a multiple of 8, including the last one. Getting it not to is disappointingly awkward.. 
    $_ = join "", do {
    my @bits = split /\t/, $_, -1;
    (map { $_ . " " x (8 - length() % 8) } @bits[0..$#bits-1]), $bits[
+-1]
};

    [download]
    (Update is untested.)

    Makeshifts last the longest.

[reply]
[d/l]
[select]
      join "", map{ $_ . (/\n/ ? "" : " " x (8 - length() & 7)) } split /\t/ ?

        p
[reply]
[d/l]
        $_ = "You\tare\tmaking\ttoo\tmany\tassumptions...";

        Makeshifts last the longest.

[reply]
[d/l]

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