Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

Before yesterday, I used only lower case letters, numbers, dot (.) and underscore(_) for directories and file naming.

Today I would like to start using more special characters. Which ones are safe (by safe I mean I will never have any problem)?

ps : I can't believe this question hasn't been asked already on this site, but I've searched for the word "naming" and read canonical questions without success (mosts are about computer names).

Edit #1 : (btw, I don't use upper case letters for file names. I don't remember why. But since a few month, I have production problems with upper case letters : Some OS do not support ascii!)

Here's what happened yesterday at work : As usual, I had to create a self signed SSL certificate. As usual, I used the name of the website for the files : www2.example.com.key www2.example.com.crt www2.example.com.csr.

Then comes the problem : Generate a wildcard self signed certificate. I did that and named the files example.com.key example.com.crt example.com.csr, which is misleading (it's a certificate for *.example.com).

I came back home, started putting some stars in apache configuration files filenames and see if it works (on a useless home computer, not even stagging).

Stars in file names really scares me : Some coworkers/vendors/... can do some script using rm find xarg that would lead to http://www.ucs.cam.ac.uk/support/unix-support/misc/horror, and already one answer talks about disaster.

Edit #2 :

Just figured that : does not need to be escaped. Anyone knows why it is not used in file names?

Edit #3 :

Let's summarize what I understood so far :

  • . and _ are safe to use in file names.
  • Special character that need to be escaped (eg space | ( * ) should be avoided.
  • Some other special caracters should be avoided for various reasons ( / - : )

What about all the other ones, like % or =?

share|improve this question

4 Answers 4

up vote 8 down vote accepted

Sounds like a recipe for disaster.

You can use anything other than / - but you might want to wrap in single quotes (') to avoid execution of special characters.

eg. $*`\|

Using special characters in file names is very much a Windows-ism - mostly taken from GUI machine administration versus command line (which doesn't lend itself to continuously having to escape file names).

The safest approach is just to stick to a-zA-Z0-9_.

share|improve this answer
Yes. It scares a lot. –  coincoin Sep 27 '12 at 11:19
I assume dot(.) and underscores(_) are safe for file names. dash (-) is not. Are there any other character that can be safely used ? –  coincoin Sep 27 '12 at 11:53
It all comes down to how you escape the file names. The safest approach is just to stick to [a-zA-Z0-9_.] –  MageStackDay Needs You ... Sep 27 '12 at 12:33
Do not use the pipe | character in filenames. –  jftuga Sep 27 '12 at 13:09
Please read my answer to avoid any ambiguity or out of context comments. I had already stated the OP should restrict his filenames to a specific subset of characters [a-zA-Z0-9_.] - hypens NOT included. The original question was What characters can you not use - and the only one you can't use is / - anything else is fine. But advisable, no. –  MageStackDay Needs You ... Sep 27 '12 at 14:19

In UNIX you can use any character except '/' because it separates directory names. Unicode characters are also fine.

share|improve this answer
And NUL, since everything is C-based under the hood. –  Ignacio Vazquez-Abrams Sep 27 '12 at 13:57

While Antonio is correct, my suggestion would be do not change your naming style, except maybe to add upper-case letters (but even that can be ambigous if other operating systems get into the mix).

This will spare you a lot of problems you might face otherwise with locales and special characters that might need to be escaped (like e.g. the space or $ sign) in shell commands.

share|improve this answer
Thank you very much. I'll update the question to provide more details. –  coincoin Sep 27 '12 at 11:13

: is generally not used in file names because Windows would refuse reading such a file. It has more restrictions with names and in particular use : as a device separator, which Unix doesn't need having a single file system hierarchy.

share|improve this answer
On OS X, a file named ooz:bar would appear in the Finder as ooz/bar. –  kojiro Sep 27 '12 at 16:04

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.