Originální popis anglicky:
glob - Globbing pathnames
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).
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.
An expression `[...]' where the first character after the leading `[' is not an
`!' matches a single character, namely any of the characters enclosed by the
brackets. The string enclosed by the brackets cannot be empty; therefore `]'
can be allowed between the brackets, provided that it is the first character.
(Thus, `[][!]' matches the three characters `[', `]' and `!'.)
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 `[--0]' matches the three characters `-', `.', `0', since `/' cannot
be matched.)
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 `[' by preceding them by a
backslash, or, in case this is part of a shell command line, enclosing them in
quotes. Between brackets these characters stand for themselves. Thus, `[[?*\]'
matches the four characters `[', `?', `*' and `\'.
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.)
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.)
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.
Of course ranges were originally meant to be ASCII ranges, so that `[ -%]'
stands for `[ !"#$%]' and `[a-z]' stands for "any lowercase
letter". Some Unix implementations generalized this so that a range X-Y
stands for the set of characters with code between the codes for X and for Y.
However, this requires the user to know the character coding in use on the
local system, and moreover, is not convenient if the collating sequence for
the local alphabet differs from the ordering of the character codes.
Therefore, POSIX extended the bracket notation greatly, both for wildcard
patterns and for regular expressions. In the above we saw three types of items
that can occur in a bracket expression: namely (i) the negation, (ii) explicit
single characters, and (iii) ranges. POSIX specifies ranges in an
internationally more useful way and adds three more types:
(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
`[aáàäâ]' (warning: Latin-1 here), that is, to
`[a[.a-acute.][.a-grave.][.a-umlaut.][.a-circumflex.]]'.
sh(1),
fnmatch(3),
glob(3),
locale(7),
regex(7)
