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.
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 offending characters, we run a search-and-replace with the empty string as the replacement text.
Recipe 3.14 explains how to run a search-and-replace with a fixed replacement text in your favorite programming language.