wiki.bash-hackers.org/syntax/expansion/globs.md

# Pathname expansion (globbing)

## General

Unlike on other platforms you may have seen, on UNIX(r), the shell is
responsible for interpreting and expanding globs ("filename wildcards").
A called program will never see the glob itself; it will only see the
expanded filenames as its arguments (here, all filenames matching
`*.log`):

    grep "changes:" *.log

The base syntax for the pathname expansion is the [pattern
matching](/syntax/pattern.md) syntax. The pattern you describe is matched
against all existing filenames and the matching ones are substituted.
Since this substitution happens **after [word
splitting](/syntax/expansion/wordsplit.md)**, all resulting filenames are
literal and treated as separate words, no matter how many spaces or
other `IFS`-characters they contain.

## Normal behaviour

- with [the set command](/commands/builtin/set.md) (`-f`, `noglob`) you can
  entirely disable pathname expansion
- when matching a pathname, the slash-character (`/`) always needs to be
  matched explicitly
- the dot at the beginning of a filename must be matched explicitly
  (also one following a `/` in the glob)
- a glob that doesn't match a filename is unchanged and remains what it
  is

## Customization

- when the shell option `nullglob` is set, non-matching globs are
  removed, rather than preserved
- when the shell option `failglob` is set, non-matching globs produce an
  error message and the current command is not executed
- when the shell option `nocaseglob` is set, the match is performed
  case-insensitive
- when the shell option `dotglob` is set, wildcard-characters can match
  a dot at the beginning of a filename
- when the shell option `dirspell` is set, Bash performs spelling
  corrections when matching directory names
- when the shell option `globstar` is set, the glob `**` will
  recursively match all files and directories. This glob isn't
  "configurable", i.e. you **can't** do something like `**.c` to
  recursively get all `*.c` filenames.
- when the shell option `globasciiranges` is set, the bracket-range
  globs (e.g. `[A-Z]`) use C locale order rather than the configured
  locale's order (i.e. `ABC...abc...` instead of e.g. `AaBbCc...`) -
  since 4.3-alpha
- the variable [GLOBIGNORE](/syntax/shellvars.md#GLOBIGNORE) can be set to
  a colon-separated list of patterns to be removed from the list before
  it is returned

### nullglob

Normally, when no glob specified matches an existing filename, no
pathname expansion is performed, and the globs are <u>**not**</u>
removed:

    $ echo "Textfiles here:" *.txt
    Textfiles here: *.txt

In this example, no files matched the pattern, so the glob was left
intact (a literal asterisk, followed by dot-txt).

This can be very annoying, for example when you drive a
[for-loop](/syntax/ccmd/classic_for.md) using the pathname expansion:

    for filename in *.txt; do
      echo "=== BEGIN: $filename ==="
      cat "$filename"
      echo "=== END: $filename ==="
    done

When no file name matches the glob, the loop will not only output stupid
text ("`BEGIN: *.txt`"), but also will make the `cat`-command fail with
an error, since no file named `*.txt` exists.

Now, when the shell option `nullglob` is set, Bash will remove the
entire glob from the command line. In case of the for-loop here, not
even one iteration will be done. It just won't run.

So in our first example:

    $ shopt -s nullglob
    $ echo "Textfiles here:" *.txt
    Textfiles here:

and the glob is gone.

### Glob characters

- \* - means 'match any number of characters'. '/' is not matched (and
  depending on your settings, things like '.' may or may not be matched,
  see above)
- ? - means 'match any single character'
- \[abc\] - match any of the characters listed. This syntax also
  supports ranges, like \[0-9\]

For example, to match something beginning with either 'S' or 'K'
followed by two numbers, followed by at least 3 more characters:

    [SK][0-9][0-9]???*

## See also

- [Introduction to expansion and substitution](/syntax/expansion/intro.md)
- [pattern matching syntax](/syntax/pattern.md)
- [the set builtin command](/commands/builtin/set.md)
- [the shopt builtin command](/commands/builtin/shopt.md)
- [list of shell options](/internals/shell_options.md)