GLOB

GLOB

NAME DESCRIPTION WILDCARD MATCHING PATHNAMES EMPTY LISTS NOTES SEE ALSO

NAME

glob - Globbing pathnames

DESCRIPTION

Long ago, in Unix V6, there was a program /etc/glob that would expand wildcard patterns. Soon afterwards this became a shell built-in.

These days there is also a library routine glob(3) that will perform this function for a user program.

The rules are as follows (POSIX 1003.2, 3.13).

WILDCARD MATCHING

A string is a wildcard pattern if it contains one of the characters `?', `*' or `[['. Globbing is the operation that expands a wildcard pattern into the list of pathnames matching the pattern. Matching is defined by:

A `?' (not between brackets) matches any single character.

A `*' (not between brackets) matches any string, including the empty string.

Character classes

An expression `[...' where the first character after the leading `[unrenderable node]' can be allowed between the brackets, provided that it is the first character. (Thus, `[[!' matches the three characters `[', `' and `!'.)

Ranges

There is one special convention: two characters separated by `-' denote a range. (Thus, `[A-Fa-f0-9' is equivalent to `[ABCDEFabcdef0123456789'.) One may include `-' in its literal meaning by making it the first or last character between the brackets. (Thus, `[-]' matches just the two characters `]' and `-', and `[--/' matches the three characters `-', `.', `/'.)

Complementation

An expression `[!...' matches a single character, namely any character that is not matched by the expression obtained by removing the first `!' from it. (Thus, `[!a-]' matches any single character except `]', `a' and `-'.)

One can remove the special meaning of `?', `*' and `[[[?*' matches the four characters `[[', `?', `*' and `'.

PATHNAMES

Globbing is applied on each of the components of a pathname separately. A `/' in a pathname cannot be matched by a `?' or `*' wildcard, or by a range like `[.-0'. A range cannot contain an explicit `/' character; this would lead to a syntax error.

If a filename starts with a `.', this character must be matched explicitly. (Thus, `rm *' will not remove .profile, and `tar c *' will not archive all your files; `tar c .' is better.)

EMPTY LISTS

The nice and simple rule given above: `expand a wildcard pattern into the list of matching pathnames' was the original Unix definition. It allowed one to have patterns that expand into an empty list, as in

xv -wait 0 *.gif *.jpg

where perhaps no *.gif files are present (and this is not an error). However, POSIX requires that a wildcard pattern is left unchanged when it is syntactically incorrect, or the list of matching pathnames is empty. With bash one can force the classical behaviour by setting allow_null_glob_expansion=true.

(Similar problems occur elsewhere. E.g., where old scripts have

rm `find . -name

new scripts require

rm -f nosuchfile `find . -name

to avoid error messages from rm called with an empty argument list.)

NOTES

Regular expressions

Note that wildcard patterns are not regular expressions, although they are a bit similar. First of all, they match filenames, rather than text, and secondly, the conventions are not the same: e.g., in a regular expression `*' means zero or more copies of the preceding thing.

Now that regular expressions have bracket expressions where the negation is indicated by a `^', POSIX has declared the effect of a wildcard pattern `[^...' to be undefined.

Character classes and Internationalization

Of course ranges were originally meant to be ASCII ranges, so that `[ -%' stands for `[[ !

(iii) Ranges X-Y comprise all characters that fall between X and Y (inclusive) in the currect collating sequence as defined by the LC_COLLATE category in the current locale.

(iv) Named character classes, like

[:alnum: [:alpha: [:blank: [:cntrl: [:digit: [:graph: [:lower: [:print: [:punct: [:space: [:upper: [:xdigit: so that one can say `[[[:lower:]' instead of `[a-z', and have things work in Denmark, too, where there are three letters past `z' in the alphabet. These character classes are defined by the LC_CTYPE category in the current locale.

(v) Collating symbols, like `[.ch.' or `[.a-acute.', where the string between `[.' and `.' is a collating element defined for the current locale. Note that this may be a multi-character element.

(vi) Equivalence class expressions, like `[=a=', where the string between `[=' and `=' is any collating element from its equivalence class, as defined for the current locale. For example, `[[[=a=]' might be equivalent to `[[a

SEE ALSO

sh(1), glob(3), fnmatch(3), locale(7), regex(7)