Wildcards in Unix

Wildcards are a little different in Unix/Linux, depending on where they are used

Wildcards in file listings

Wildcards

? any single character, except a leading dot
* zero or more characters, except a leading dot
[ ] defines a class of characters ( - for range, ! to exclude)

Examples:

[abc]?? 3 character filename beginning with "a", "b", or "c".
[1-9][A-Z] 2 character filename starting with a number, and ending with an uppercase letter.
[!A-Z]?? 3 character filename that does not begin with an uppercase letter.
*e[0-9]f any file ending with "e", a single number, and "f".

Note:this is similar to (but not the same as) pattern matching we saw with grep.

Consider the following:

-rw-r--r--. 1 root      root         0 Jul 21 09:19 bap
-rw-r--r--. 1 root      root         0 Jul 21 09:19 bapper
-rw-r--r--. 1 root      root         0 Jul 21 09:20 bapperization
-rw-r--r--. 1 root      root         0 Jul 21 09:27 bill5
-rw-r--r--. 1 root      root         0 Jul 21 09:19 cap
-rw-r--r--. 1 root      root         0 Jul 21 09:26 cat
-rw-r--r--. 1 root      root         0 Jul 21 09:27 cat9
-rw-r--r--. 1 root      root         0 Jul 21 09:19 dap
-rw-r--r--. 1 root      root         0 Jul 21 09:26 dog
-rw-r--r--. 1 root      root         0 Jul 21 09:19 fap
-rw-r--r--. 1 root      root         0 Jul 21 09:27 jason7
-rw-r--r--. 1 root      root         0 Jul 21 09:28 leonard679
-rw-r--r--. 1 root      root         0 Jul 21 09:27 mouse
-rw-r--r--. 1 root      root         0 Jul 21 09:27 nathan3

ls -al [bc]a*    will return

-rw-r--r--. 1 root root 0 Jul 21 09:19 bap
-rw-r--r--. 1 root root 0 Jul 21 09:19 bapper
-rw-r--r--. 1 root root 0 Jul 21 09:20 bapperization
-rw-r--r--. 1 root root 0 Jul 21 09:19 cap
-rw-r--r--. 1 root root 0 Jul 21 09:26 cat
-rw-r--r--. 1 root root 0 Jul 21 09:27 cat9

ls -al *[0-9]    will return

-rw-r--r--. 1 root root 0 Jul 21 09:27 bill5
-rw-r--r--. 1 root root 0 Jul 21 09:27 cat9
-rw-r--r--. 1 root root 0 Jul 21 09:27 jason7
-rw-r--r--. 1 root root 0 Jul 21 09:28 leonard679
-rw-r--r--. 1 root root 0 Jul 21 09:27 nathan3


Quiz type questions:

what will the following return?

ls -al *[!0-9]

ls -al *[0-9][0-9]

ls -al ?a?

Wildcards in grep

 .
any single character
* match the preceding character zero or more times
+
 match the preceding character one or more times
[ ] defines a class of characters ( - for range, ^ to exclude)

Anchors in grep

^
 Match to the beginning of a line
$
 Match to the end of a line


Examples:

[abc].. 3 character filename beginning with "a", "b", or "c".
[1-9][A-Z] 2 character filename starting with a number, and ending with an uppercase letter.
[^A-Z].. 3 character filename that does not begin with an uppercase letter.

>cat file

big
bad bug
bag
bigger
boogy

>grep b.g file

big
bad bug
bag
bigger

notice that boogy didn't match, since the "." matches exactly one character.

The repetition meta-characters * and +

    the expression consisting of a character followed by a star matches any number (possibly zero) of repetitions of that character. In particular, the expression ".*" matches any string, and hence acts as a "wildcard". Note that ".*" can match NO characters, but ".+" must have at least one character.

Examples:

>cat file
big
bad bug
bag
bigger
boogy

   
Wildcards #1

>grep "b.*g" file
big
bad bug
bag
bigger
boogy

   
Wildcards #2

>grep "b.*g." file
bigger
boogy

Other examples:

grep "^[0-9]" testfile  <---- `find all lines in file testfile that begin with a digit

grep "^[^0-9]" testfiel <----- find all lines in file testfile that begin with any character OTHER than a digit

grep "cat+" testfile <-----find all lines in file testfile that contain either cat catt cattt cattttt (etc.)