Bash

From Luke Jackson

Globbing

Globbing is the name for the shell's filename expansion capabilities. When the shell parses a command line, it looks in each token ( word, if you like ) for the special characters:

•  ? - One of any character
• \* - Zero or more of any character
• [ - Introduces a character class

If it finds any of these, it replaces token with a list of all filenames that match the pattern that the token represents. The ? character is a wild card that stands for 'one of any character' -- except the dot ( . ). It must match one character: 'abc?' does not match 'abc', but does match 'abcd'. The * character matches zero or more of any character. The pattern 'abc*' matches 'abc' as well as 'abcd' and 'abcdefgh...'. The [ character introduces a character class, a list of single characters that can be matched. The pattern 'abc[de]' matches 'abcd' and 'abce' but not 'abc' nor 'abcg'. If no match is found, the meta characters can be taken as literally what the are. If you do not want a meta character expanded, you need to escape it with a backslash, e.g., a file named 'abc*' would have to be typed 'abc\*' to avoid expansion. The best way to avoid problems, though, is to avoid special characters -- don't use anything in a filename that you have to escape.

Brace Expansion

On a similar subject, the shell also does brace expansion ( which is not globbing -- globbing is done to names from the filesystem ). If it sees a { character in a token, it checks to see if there is a pair of braces containing a properly formatted list of text strings ( at least one comma and no spaces ) then generates a list of tokens from the expansions. Note well that it does not do filename matching in order to determine whether to generate the token. Given the command

chown 701 public_html/chap{0{8,9},1{0,1,2}}

the last token will be expanded to the list: chap08, chap09, chap10, chap11, and chap12 ( the command will attempt to operate on the all the paths, possibly failing on any path that does not exist ). Note that you can nest braces.