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

NAME

     glob - globbing pathnames

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 char-
     acters '[', ']' and '!'.)

     Ranges

     There is one special convention: two characters separated by '-' denote
     a    range.    (Thus,   "[A-Fa-f0-9]"   is   equivalent   to   "[ABCDE-
     Fabcdef0123456789]".)  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 explic-
     itly.   (Thus,  rm * will not remove .profile, and tar c * will not ar-
     chive 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 com-
     mand:

         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

 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 nega-
     tion 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 cod-
     ing 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_COL-
     LATE 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  "[a]",  that  is,  to "[a[.a-acute.][.a-grave.][.a-
     umlaut.][.a-circumflex.]]".