4.2 File and Directory Wildcards

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

Notation	Definition
*	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, with the exception of any starting with a period. To match all your dot files, try .??* .
?	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 chap[12] would match chap1 or chap2 . 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  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.