подстановка имен путей (globbing pathnames)
Имя (Name)
glob - globbing pathnames
Описание (Description)
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).
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
'[' 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 '!'.)
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 "[--0]" matches the three characters '-', '.', '0',
since '/' cannot be matched.)
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 '[' 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 '\'.
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 containing an
explicit '/' character is syntactically incorrect. (POSIX
requires that syntactically incorrect patterns are left
unchanged.)
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 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.)
Примечание (Note)
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:
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 undefined.
Character classes and internationalization
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 current 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 multicharacter
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 "[aáaäâ]", that is, to
"[a[.a-acute.][.a-grave.][.a-umlaut.][.a-circumflex.]]".
Смотри также (See also)
sh(1), fnmatch(3), glob(3), locale(7), regex(7)
