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RE: strip multiple spaces

by autark (Friar)
on Aug 01, 2000 at 05:23 UTC ( #25382=note: print w/replies, xml ) Need Help??

in reply to strip multiple spaces

You have used the regex / / (match one space) as delimiter for split. Unfortunatly the string in $line contains several consecutive spaces, so perl does what it's told, split on one space. As an example:
$line = "foo bar"; print ++$i, ". $_\n" for split / /, $line;
$line is assigned the string "", where the '.' is meant to be space (it's more visible). That would output:
1. foo
3. bar
It prints out three lines, one which is empty (because there is nothing between the two spaces). So we have to deal with more than one whitespace. We could do this: split /\s+/, $line Now, perl will look for 1 or more spaces when trying to figure out where to split - and in your example that would probabely work out just fine. (don't use \s* as delimiter as that would match everywhere)
But, what if your string looked something like this: $line = "  foo   bar  "; Using \s+ as delimiter now would garble things up again. It would return an extra element (which is empty) at the front. How do we fix this then ? Well, the solution may look at bit counterintuitive from what we have learned so far: split " ", $line Hm, wouldn't that just match one single space again ? Well, it should, but it doesn't. This is a special case in perl, and if we apply that to our test case we will get the following result:
1. foo
2. bar
Ah, just what we want (in almost all cases I would dare to say). As an interesting note, consider the following:
perl -MO=Deparse -e 'split " "' split(/\s+/, $_, 0);
perl -MO=Deparse -e 'split /\s+/' split(/\s+/, $_, 0);
generates the exact same output - but we know that the semantics is not the same. But as long as perl does The Right Thing(TM), I'm happy :-)


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