Adriano Rodrigues Ferreira wrote:
>
> My problem is:
>
> Given a (multiline) string, I want a function which remove all leading and trailing
> white-space (as given by \s).
>
> Examples:
> " abbds \n sass " => "abbds \n sass"
> " a " => "a"
> " \n first phrase \n second phrase \n \n" => "first phrase \n second
>phrase"
> " \017 a " => "\017 a"
> " " => ""
>
> These also show the following cases:
> * space in between goes on unchanged,
> * also characters which are not space and which does not match \w (like \017), must
> remain unchanged too,
> * strings with only spaces map into the empty string
>
> I have tried
>
> sub trim {
> my ($text) = @_;
> $text =~ m<^\s*(?=\S)(.*)(?=\S)\s*$>s;
> return $2;
> }
>
> The rationale is: (1) scan leading spaces, (2) match a zero-length assertion when
> a non space is encountered, (3) scan everything collecting into $2 until
> (4) a zero-length assertion for a non space is matched, (5) followed
> by trailing spaces. Then I catch $2.
>
> But it does not work. If I change the pattern to
> ^\s*\b(.*)\b\s*$
> and return $1, it works except for cases like " \017 a ".
> I'm not sure I have understood how to use (?= ). Is \b equivalent
> to (?=\w) ?
>
> I would like the solution as concise and simple as possible.
Have you looked at the solution in the FAQ?
perldoc -q "strip blank space"
How do I strip blank space from the beginning/end of a
string?
Although the simplest approach would seem to be:
$string =~ s/^\s*(.*?)\s*$/$1/;
Not only is this unnecessarily slow and destructive, it
also fails with embedded newlines. It is much faster to
do this operation in two steps:
$string =~ s/^\s+//;
$string =~ s/\s+$//;
Or more nicely written as:
for ($string) {
s/^\s+//;
s/\s+$//;
}
This idiom takes advantage of the `foreach' loop's alias�
ing behavior to factor out common code. You can do this
on several strings at once, or arrays, or even the values
of a hash if you use a slice:
# trim whitespace in the scalar, the array,
# and all the values in the hash
foreach ($scalar, @array, @hash{keys %hash}) {
s/^\s+//;
s/\s+$//;
}
John
--
use Perl;
program
fulfillment
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