FAQ 4.32 How do I strip blank space from the beginning/end of a string?

Discussion in 'Perl Misc' started by PerlFAQ Server, Feb 25, 2011.

  1. This is an excerpt from the latest version perlfaq4.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 .

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

    4.32: How do I strip blank space from the beginning/end of a string?

    (contributed by brian d foy)

    A substitution can do this for you. For a single line, you want to
    replace all the leading or trailing whitespace with nothing. You can do
    that with a pair of substitutions:

    s/^\s+//;
    s/\s+$//;

    You can also write that as a single substitution, although it turns out
    the combined statement is slower than the separate ones. That might not
    matter to you, though:

    s/^\s+|\s+$//g;

    In this regular expression, the alternation matches either at the
    beginning or the end of the string since the anchors have a lower
    precedence than the alternation. With the "/g" flag, the substitution
    makes all possible matches, so it gets both. Remember, the trailing
    newline matches the "\s+", and the "$" anchor can match to the absolute
    end of the string, so the newline disappears too. Just add the newline
    to the output, which has the added benefit of preserving "blank"
    (consisting entirely of whitespace) lines which the "^\s+" would remove
    all by itself:

    while( <> ) {
    s/^\s+|\s+$//g;
    print "$_\n";
    }

    For a multi-line string, you can apply the regular expression to each
    logical line in the string by adding the "/m" flag (for "multi-line").
    With the "/m" flag, the "$" matches *before* an embedded newline, so it
    doesn't remove it. This pattern still removes the newline at the end of
    the string:

    $string =~ s/^\s+|\s+$//gm;

    Remember that lines consisting entirely of whitespace will disappear,
    since the first part of the alternation can match the entire string and
    replace it with nothing. If you need to keep embedded blank lines, you
    have to do a little more work. Instead of matching any whitespace (since
    that includes a newline), just match the other whitespace:

    $string =~ s/^[\t\f ]+|[\t\f ]+$//mg;



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

    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 25, 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. Ken Fine
    Replies:
    2
    Views:
    105
    Ken Fine
    Jan 7, 2004
  2. Aquila
    Replies:
    35
    Views:
    441
    Mathieu Bouchard
    Mar 31, 2005
  3. Jesse B.
    Replies:
    9
    Views:
    221
    Jesse B.
    Mar 27, 2010
  4. Sandy Lewanscheck

    strip <br> and \n in beginning of string

    Sandy Lewanscheck, Jan 7, 2004, in forum: Javascript
    Replies:
    0
    Views:
    100
    Sandy Lewanscheck
    Jan 7, 2004
  5. yelipolok
    Replies:
    4
    Views:
    244
    John W. Krahn
    Jan 27, 2010
Loading...

Share This Page