glob — globbing pathnames
Long ago, in UNIX V6, there was a program
/etc/glob that would expand wildcard
patterns. Soon afterward 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.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, "
is equivalent to "
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
the three characters '−', '.', '0', since '/' cannot
An expression "
[!...]" matches a single
character, namely any character that is not matched by the
expression obtained by removing the first '!' from it.
[!]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,
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 behavior using this command:
shopt −s nullglob
(Similar problems occur elsewhere. For example, 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: for example, 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
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
(iii) Ranges X−Y comprise all characters that fall
between X and Y (inclusive) in the current collating
sequence as defined by the
LC_COLLATE category in the current
(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
and have things work in Denmark, too, where there are three
letters past 'z' in the alphabet. These character classes
are defined by the
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
(vi) Equivalence class expressions, like "
[=a=]", where the string
=]" is any
collating element from its equivalence class, as defined
for the current locale. For example, "
[[=a=]]" might be
equivalent to "
that is, to "
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Copyright (c) 1998 Andries Brouwer
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2003-08-24 fix for / by John Kristoff + joey