NAME | DESCRIPTION | NOTES | SEE ALSO | COLOPHON

GLOB(7)                   Linux Programmer's Manual                  GLOB(7)

NAME         top

       glob - globbing pathnames

DESCRIPTION         top

       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.)

NOTES         top

   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 "[aáàäâ]", that is, to "[a[.a-acute.][.a-
       grave.][.a-umlaut.][.a-circumflex.]]".

SEE ALSO         top

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

COLOPHON         top

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Linux                            2016-10-08                          GLOB(7)