When you have a number of files named in series (for example, chap1.doc to chap12.doc ) 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 characteristics detailed in Table 4-1 are true.
Table 4-1. Shell wildcards
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 chap0.txt chap2.txt chap5.txt cold.txt chap1a.old.txt chap3.old.txt chap6.txt haha.txt chap1b.txt chap4.txt chap7.txt oldjunk $ ls chap?.txt chap0.txt chap4.txt chap6.txt chap2.txt chap5.txt chap7.txt $ ls chap[3-7]* chat3.old.txt chap4.txt chap5.txt chap6.txt chap7.txt $ ls chap??.txt chap1b.txt $ ls *old* chap1a.old.txt chap3.old.txt cold.txt oldjunk $ ls *a*a*
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, both the cat and less programs display files on the screen. cat streams a file's contents until end of file, while less shows the file one screenfull at a time. Let's say you want to display files chap3.old.txt and chap1a.old.txt . Instead of specifying these files individually, you could enter the command as:
$ less *.old.txt
This is equivalent to less chap1a.old.txt chap3.old.txt .
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 . However, there's one important difference when you use less */summary : the names will be alphabetized, so Apr/summary would be first in the list.