mirror of
https://github.com/rawiriblundell/wiki.bash-hackers.org
synced 2024-11-02 09:03:06 +01:00
114 lines
4.2 KiB
Markdown
114 lines
4.2 KiB
Markdown
# 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)
|