Linux Wildcards - Standard

"Unix is simple. It just takes a genius to understand its simplicity." – Dennis Ritchie

One of the advantage of Unix or *nix operating system is its simplicity. Beginners might find it hard to agree with me. But once you have familiarized with the OS and learned how to make use of it, you will discover the simplicity offered by Unix / *nix operating systems. Wildcards are one such concept which make Unix / *nix simple

Wildcards are symbol used to replace or represent one or more characters. i.e. wildcard expressions can be used by commands to perform action on multiple files at a time.Wildcards can be used in many ways and helps you to keep things simple and easy.

There are mainly 2 ways by which a wild cards can be used. One is the Standard (globbing) wildcard, usually used by shell and the second is regular expression (regex) wildcard used mainly with text searching  and manpulation commands like grep.

In this post we are going to see Standard wildcards. The most used standard wildcards are as follows

• * (Asterisk)
• ? (Question Mark)
• { } (Curly Bracket)
• [ ] (Square Bracket)
• [!] (Exclamation within Square Bracket)
• \ (Back slash)

Before going into the details, displayed below is the ls -l output of a my home directory. Rest of the post will be explained from within this directory

* (Asterisk) 

One of the most commonly used wildcard. This  can represent any number of characters, numerals or special characters. * can be used in cases like listing all files with .txt files in a directory

For example to long list all  .txt files, enter

ls -l *.txt

Sample Output:

-rw-rw-r--  1 calypso calypso    2 Feb 14 15:21 demo.txt
-rw-rw-r--  1 calypso calypso    10 Feb 17 17:06 file1.txt
-rw-rw-r--  1 calypso calypso    10 Feb 17 17:06 file2.txt
-rw-rw-r--  1 calypso calypso    10 Feb 17 17:06 file3.txt
-rw-rw-r--  1 calypso calypso    10 Feb 17 17:06 file4.txt
-rw-rw-r--  1 calypso calypso    10 Feb 17 17:06 file5.txt
-rw-r--r--. 1 calypso calypso 4244 Sep 26  2011 README.txt

Or to list files starting with httpd, enter

ls  httpd*

Sample Output:

httpd-2.2.3-53.el5_7.3.i386.rpm  httpd-devel-2.2.3-53.el5_7.3.i386.rpm  httpd-manual-2.2.3-53.el5_7.3.i386.rpm

? (Question Mark)

Question mark (?) is the wild card  used to represent a single character  i.e. Question mark (?) in a command line argument can represent any letter or number between a-z and 0-9.

For example to copy 5 files named file1.txt, file2.txt, file3.txt, file4.txt and file5.txt from current directory to Downloads directory also located in my home directory enter

cp file?.txt Downloads/

Similarly, two question marks in succession represents two character in succession, three question marks in succession would represent three characters in succession and so on. i.e

ls -l ????

will list all files with exactly four character length

{ } (Curly Bracket) 

Curly Brackets are used to represent multiple terms separated by commas and each term can be a character,  group of character,  or a wild card

For example to list only file1.txt and file2.txt, enter

ls file{1,2}.txt

Similarly to remove file1.txt, file4.txt and file5.txt, enter:

rm file{1,4,5}.txt

[ ] (Square Bracket)

Square Backet is used to specify a range. i.e. /dev/sd[a-c] may represent /dev/sda, /dev/sdb, /dev/sdc.

For example to list file1.txt, file2.txt, file3.txt, file4.txt and file5.txt, enter

ls file[1-5].txt

[!] (Exclamation within Square Bracket)

Represent everything except the character or range mentioned within the  [ ](square bracket). i.e. [!m] can represent any character between a-z except m.

For example

ls file[!2].txt

will display all file?.txt files except file2.txt
Sample Output

file1.txt file3.txt file4.txt file5.txt

\ (Back slash) 

 Back slash or the escape character is used to protect special character. Consider you have copied a file named 'My File.txt' created from a windows machine to your linux box and you want to view the contents of the file using cat command

cat My File.txt

Sample Output

cat: My: No such file or directory
cat: File.txt: No such file or directory

In the above example, cat command thinks My File.txt are two different files, My and File.txt, since there is a space in between the file name. The correct method is to use '\' before the space

These are the different Simple Wildcards used in Unix/*nix systems. Hope you got an idea on wild cards. Like I said before wildcards are very handy and their usage can be improvised based on your requirement.  The regex wildcards will be explained later.