FAQ 6.6 How do I substitute case insensitively on the LHS while preserving case on the RHS?

Discussion in 'Perl Misc' started by PerlFAQ Server, Feb 8, 2011.

  1. This is an excerpt from the latest version perlfaq6.pod, which
    comes with the standard Perl distribution. These postings aim to
    reduce the number of repeated questions as well as allow the community
    to review and update the answers. The latest version of the complete
    perlfaq is at http://faq.perl.org .

    --------------------------------------------------------------------

    6.6: How do I substitute case insensitively on the LHS while preserving case on the RHS?

    Here's a lovely Perlish solution by Larry Rosler. It exploits properties
    of bitwise xor on ASCII strings.

    $_= "this is a TEsT case";

    $old = 'test';
    $new = 'success';

    s{(\Q$old\E)}
    { uc $new | (uc $1 ^ $1) .
    (uc(substr $1, -1) ^ substr $1, -1) x
    (length($new) - length $1)
    }egi;

    print;

    And here it is as a subroutine, modeled after the above:

    sub preserve_case($$) {
    my ($old, $new) = @_;
    my $mask = uc $old ^ $old;

    uc $new | $mask .
    substr($mask, -1) x (length($new) - length($old))
    }

    $string = "this is a TEsT case";
    $string =~ s/(test)/preserve_case($1, "success")/egi;
    print "$string\n";

    This prints:

    this is a SUcCESS case

    As an alternative, to keep the case of the replacement word if it is
    longer than the original, you can use this code, by Jeff Pinyan:

    sub preserve_case {
    my ($from, $to) = @_;
    my ($lf, $lt) = map length, @_;

    if ($lt < $lf) { $from = substr $from, 0, $lt }
    else { $from .= substr $to, $lf }

    return uc $to | ($from ^ uc $from);
    }

    This changes the sentence to "this is a SUcCess case."

    Just to show that C programmers can write C in any programming language,
    if you prefer a more C-like solution, the following script makes the
    substitution have the same case, letter by letter, as the original. (It
    also happens to run about 240% slower than the Perlish solution runs.)
    If the substitution has more characters than the string being
    substituted, the case of the last character is used for the rest of the
    substitution.

    # Original by Nathan Torkington, massaged by Jeffrey Friedl
    #
    sub preserve_case($$)
    {
    my ($old, $new) = @_;
    my ($state) = 0; # 0 = no change; 1 = lc; 2 = uc
    my ($i, $oldlen, $newlen, $c) = (0, length($old), length($new));
    my ($len) = $oldlen < $newlen ? $oldlen : $newlen;

    for ($i = 0; $i < $len; $i++) {
    if ($c = substr($old, $i, 1), $c =~ /[\W\d_]/) {
    $state = 0;
    } elsif (lc $c eq $c) {
    substr($new, $i, 1) = lc(substr($new, $i, 1));
    $state = 1;
    } else {
    substr($new, $i, 1) = uc(substr($new, $i, 1));
    $state = 2;
    }
    }
    # finish up with any remaining new (for when new is longer than old)
    if ($newlen > $oldlen) {
    if ($state == 1) {
    substr($new, $oldlen) = lc(substr($new, $oldlen));
    } elsif ($state == 2) {
    substr($new, $oldlen) = uc(substr($new, $oldlen));
    }
    }
    return $new;
    }



    --------------------------------------------------------------------

    The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
    are not necessarily experts in every domain where Perl might show up,
    so please include as much information as possible and relevant in any
    corrections. The perlfaq-workers also don't have access to every
    operating system or platform, so please include relevant details for
    corrections to examples that do not work on particular platforms.
    Working code is greatly appreciated.

    If you'd like to help maintain the perlfaq, see the details in
    perlfaq.pod.
     
    PerlFAQ Server, Feb 8, 2011
    #1
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Guest
    Replies:
    5
    Views:
    635
    Kai-Uwe Bux
    Jan 31, 2006
  2. Guest
    Replies:
    1
    Views:
    465
    Luke Meyers
    Jan 31, 2006
  3. tomaszewski.p
    Replies:
    4
    Views:
    815
    Tom Anderson
    Sep 12, 2008
  4. Knute Johnson
    Replies:
    0
    Views:
    425
    Knute Johnson
    Sep 11, 2008
  5. Roedy Green
    Replies:
    0
    Views:
    425
    Roedy Green
    Sep 12, 2008
Loading...

Share This Page