How to Match and Validate Spaces in PHP Regular Expressions?

Matching Spaces in Regular Expressions

When working with regular expressions, it's often necessary to match whitespace characters, including spaces. This question seeks to address matching spaces in PHP regular expressions, particularly for the purpose of validating inputs containing only letters, numbers, and spaces.

To match a single space character, use the expression " " (two spaces within quotes). For matching one or more spaces, use " "* (two spaces followed by an asterisk) or " " (one space followed by a plus).

For more generalized spacing, consider using "[ X]" (a physical tab character) or " X*" or "[ X] ". These expressions are compatible with most regex engines.

If using newer regex engines, "s" and its variations can be employed for whitespace matching. In PHP, you can refer to the PHP manual for specific regex syntax.

To remove non-valid characters while allowing spaces, use a regex like:

/[^a-zA-Z0-9 ]/

To further ensure there's only one space between words and none at the start or end, use the following regex steps:

/ +/ -> " " (convert multiple spaces to single space)
^ -> "" (remove space from start)
$ -> "" (remove space from end)

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