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.

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    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:


    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:


    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( <> ) {
    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;


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