PHP Regex for filename

Question

I made the user possible to change file names through a textarea, but now I'm having a regex problem.

As I see for Windows 7, these characters only are not allowed for filenames:

\ / : * ? < > |

But I stubbornly, perhaps also wisely, choose to minimize the regex to ONLY these special characters:

- _ .

All the others should have to be cut.

Can someone help me out with this regex?

preg_replace all but: A-Za-z0-9 and - _ .

I still really don't get the hang of it.

or a simple str_replace(); to replace the unneded characters with an empty string like this '' — rsz
– rsz, Commented Dec 4, 2012 at 15:17
[^A-Za-z0-9\-_.]. "anything that ISN'T one of the following..." — Marc B
– Marc B, Commented Dec 4, 2012 at 15:20
Have you tried anything? A google search for regex filename gives you plenty of useful results. — Tchoupi
– Tchoupi, Commented Dec 4, 2012 at 15:20
@IanOverton Althoguh it wouldn't quite work, as the '-' character would act as a range. — Paul S
– Paul S, Commented Dec 4, 2012 at 15:24

Paul S · Accepted Answer · 2012-12-04 15:21:27Z

16

preg_replace('/[^A-Za-z0-9 _ .-]/', '', $filename);

The [] is a character class and the ^ negates it. So it literally matches anything other than the chars in that group.

Note that - is at the end, as it is a special range character if used elsewhere, e.g. 0-9

answered Dec 4, 2012 at 15:21

Paul S

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2 Comments

ESP32 Over a year ago

should it be \. ? Dot means any character.

alexcm Jan 9 at 15:13

@ESP32 only outside "[]" as inside them you are specifying characters. So "." which means everything outside the "[]", is asumed as a character inside them.

newfurniturey · Accepted Answer · 2016-01-01 20:26:32Z

4

Your question has the character-set pretty-much laid out already. You'll just need to plug it into preg_replace() to get it going.

Try this:

$filename = preg_replace('/[^a-zA-Z0-9_.-]/', '', $filename);

The ^ at the beginning of the character set, surrounded by [], states to not-match the list of characters. Therefore, the line can be read as "replace the characters that are not the following".

edited Jan 1, 2016 at 20:26

answered Dec 4, 2012 at 15:21

newfurniturey

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