Regular Expressions Cookbook, 2nd Edition

8.25. Strip Invalid Characters from Filenames

Problem

You want to strip a string of characters that aren’t valid in Windows filenames. For example, you have a string with the title of a document that you want to use as the default filename when the user clicks the Save button the first time.

Solution

Regular expression

[\\/:"*?<>|]+

Regex options: None

Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Replacement

Leave the replacement text blank.

Replacement text flavors: .NET, Java, JavaScript, PHP, Perl, Python, Ruby

Discussion

The characters \/:"*?<>| are not valid in Windows filenames. These characters are used to delimit drives and folders, to quote paths, or to specify wildcards and redirection on the command line.

We can easily match those characters with the character class ‹[\\/:"*?<>|]›. The backslash is a metacharacter inside character classes, so we need to escape it with another backslash. All the other characters are always literal characters inside character classes.

We repeat the character class with a ‹+› for efficiency. This way, if the string contains a sequence of invalid characters, the whole sequence will be deleted at once, rather than character by character. You won’t notice the performance difference when dealing with very short strings, such as filenames, but it is a good technique to keep in mind when you’re dealing with larger sets of data that are more likely to have longer runs of characters that you want to delete.

Since we just want to delete the ...