Safe Characters for File Names

* ASCII Characters

 0-9 A-Z a-z
 Space ! " # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ `
 { | } ~ (33 specials)

* Bourne shell metacharacters

 Space | & ; ( ) < > Newline Tab

* Other significant characters

 ? [ ] $ { } ` \ ' " * ! #

* WWW Security FAQ

The World Wide Web Security FAQ (<http://www.w3.org/Security/Faq/>)
gives the following list of unsafe characters (for all user-supplied
text passed to a shell):

& ; ` ' \ " | * ? ~ < > ^ ( ) [ ] { } $ NEWLINE RETURN

This excludes '~' and '^', which I had considered safe, and permits
'!', '#', SPACE, and TAB, which I considered problematic.

I'll take a cautious approach and exclude the new characters the FAQ
considers problematic in addition to the ones I identified myself.

* Safe characters

Most unix systems place no restrictions on valid characters for file
names. However non-printing and other characters are inconvenient for
file manipulation, and shell metacharacters in text processed by the
shell can pose a security risk. Therefore safe characters are
alphanumerics and a conservatively selected subset of special
characters.

 0-9 A-Z a-z
 % + , - . / : = @ _ (10 specials)

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