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PHP/REGEX: Remove periods and duplicate slashes

Posted on 2011-03-16
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Last Modified: 2012-05-11
The following code works exactly the way I want it to, however I would rather the last two lines be combined into one regular expression.

First, all periods should be removed.  Then, all slashes and groups of slashes should be converted to a single slash (DIRECTORY_SEPARATOR)

All slashes should be converted to the DIRECTORY_SEPARATOR.

So, on Windows, this:
..///my\\\\..///sub\\dir/

Should become this:
\my\sub\dir\

And on Linux, this:
..///my\\\\..///sub\\dir/
Should become this:
/my/sub/dir/

<?php

$source = "..///my\\\\\\\\..///sub\\\\dir/";

// The following code works exactly the way I want it to, however I would rather the last two lines be combined into one regular expression.
$source = str_replace('.','',$source);
$result = preg_replace('#[\\\\/]+#', DIRECTORY_SEPARATOR, $source);

echo $result;

?>

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Question by:hankknight
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6 Comments
 
LVL 35

Assisted Solution

by:Terry Woods
Terry Woods earned 350 total points
ID: 35153118
My first thought is: Why? If it works, and runs quickly, and is understandable (and thus maintainable), then you don't really have a problem to solve!

However, it may not be safe to be removing all periods, as it can be part of a directory name.

This appears to work, and allows periods in directory names to remain:

$result = preg_replace('#(^|[/\\]*)\.\.[/\\]+|[\\/]+#', DIRECTORY_SEPARATOR, $source);

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LVL 7

Assisted Solution

by:lexlythius
lexlythius earned 150 total points
ID: 35153123
<?php

$source = "..///my\\\\\\\\..///sub\\\\dir/";

$result = preg_replace(array('/\.+/', '#[\\\\/]+#'), array('', DIRECTORY_SEPARATOR), $source);

echo $result;

?>
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LVL 35

Expert Comment

by:Terry Woods
ID: 35153124
Even so, if your code may be maintained by someone else in the future, it would be clearer to separate it into 2 replaces.
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LVL 7

Expert Comment

by:lexlythius
ID: 35153128
Note that preg_replace accepts arrays as parameters to do succesive replacements.
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LVL 35

Expert Comment

by:Terry Woods
ID: 35153139
Minor correction, to allow for directory names like dir.. :
$result = preg_replace('#(^|[/\\]+)\.\.[/\\]+|[\\/]+#', DIRECTORY_SEPARATOR, $source);
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LVL 35

Accepted Solution

by:
Terry Woods earned 350 total points
ID: 35153167
My recommended approach for maintainability:

$result = preg_replace('#[\\/]+#', DIRECTORY_SEPARATOR, $source); #remove excess separators
$result = preg_replace('#(^|[\\/])\.\.?[\\/]#', DIRECTORY_SEPARATOR, $result); #remove references to the special cases .. and . as directories

Things that might still trip you up (but probably won't matter):
1. Removing a .. from part of a path may of course make the resulting path invalid
2. linux paths can also have / and \ as part of the directory name - it just needs to be escaped with a \ character
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