File and Directory Wildcards (Learning the Unix Operating System, 5th Edition)

4.2. File and Directory Wildcards

When you have a number of files named in series (for example, chap1 to chap12) or filenames with common characters (such as aegis, aeon, and aerie), you can use wildcards to specify many files at once. These special characters are * (asterisk), ? (question mark), and [ ] (square brackets). When used in a file or directory name given as an argument on a command line, the following is true:

*: An asterisk stands for any number of characters in a filename. For example, ae* would match aegis, aerie, aeon, etc. if those files were in the same directory. You can use this to save typing for a single filename (for example, al* for alphabet.txt) or to choose many files at once (as in ae*). A * by itself matches all file and subdirectory names in a directory.
?: A question mark stands for any single character (so h?p matches hop and hip, but not help).
[]: Square brackets can surround a choice of single characters (i.e., one digit or one letter) you'd like to match. For example, [Cc]hapter would match either Chapter or chapter, but [ch]apter would match either capter or hapter. Use a hyphen (-) to separate a range of consecutive characters. For example, chap[1-3] would match chap1, chap2, or chap3.

The following examples show the use of wildcards. The first command lists all the entries in a directory, and the rest use wildcards to list just some of the entries. The last one is a little tricky; it matches files whose names contain two (or more) a's.

$ ls
chap10       chap2        chap5     cold
chap1a.old   chap3.old    chap6     haha
chap1b       chap4        chap7     oldjunk
$ ls chap?
chap2    chap5    chap7
chap4    chap6
$ ls chap[5-7]
chap5    chap6    chap7
$ ls chap[5-9]
chap5    chap6    chap7
$ ls chap??
chap10   chap1b
$ ls *old
chap1a.old   chap3.old    cold
$ ls *a*a*
chap1a.old   haha

Wildcards are useful for more than listing files. Most Unix programs accept more than one filename, and you can use wildcards to name multiple files on the command line. For example, the less program displays a file on the screen. Let's say you want to display files chap3.old and chap1a.old. Instead of specifying these files individually, you could enter the command as:

$ less *.old

This is equivalent to "less chap1a.old chap3.old".

Wildcards match directory names, too. You can use them anywhere in a pathname--absolute or relative--though you still need to separate directory levels with slashes (/). For example, let's say you have subdirectories named Jan, Feb, Mar, and so on. Each has a file named summary. You could read all the summary files by typing "less */summary". That's almost equivalent to "less Jan/summary Feb/summary ..." but there's one important difference: the names will be alphabetized, so Apr/summary would be first in the list.