Using expand and unexpand commands

In the following tutorial, we will look at how to use the "expand" and "unexpand" commands.

Expand Command

The "expand" command is used to convert tabs in files to spaces. When no file is passed or "-" is passed, then standard input is read.

Basic Syntax of command: expand [OPTION]... [FILE]...

The following text file "file1" will be used in the examples that follow. The contents of "file1" contains tabs between each field. This can be verified by using the "cat -vet" option to display hidden characters.


$ cat file1
One	Two	Three	Four	Five	six	seven
One	Two	Three	Four	Five	six	seven
One	Two	Three	Four	Five	six	seven
One	Two	Three	Four	Five	six	seven
One	Two	Three	Four	Five	six	seven
One	Two	Three	Four	Five	six	seven
One	Two	Three	Four	Five	six	seven
One	Two	Three	Four	Five	six	seven

$ cat -vet file1
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$

By using the "cat -vet" option against file1, we can see that the tabs are represented by the "I^" character. The "$" denotes a line feed. Now if we use the expand command, we can convert these tabs into spaces. We will use the expand command and create a new file called "file2".


$ expand file1 > file2

$ cat -vet file2
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$

Expand Command Options:


       -i, --initial
              do not convert tabs after non blanks

       -t, --tabs=NUMBER
              have tabs NUMBER characters apart, not 8

       -t, --tabs=LIST
              use comma separated list of explicit tab positions

       --help display this help and exit

       --version
              output version information and exit

Unexpand Command

The "unexpand" command is used to convert space characters (blanks) into tabs in each file.

Basic Syntax of command: unexpand [OPTION]... [FILE]...

Below is an example using the file "file2" that we created earlier. From the "cat -vet" command, we can see that there are no tabs present within file2. We will now use the "unexpand command to convert these to tabs and then create a new file called "file3".


$ cat -vet file2
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$
One     Two     Three   Four    Five    six     seven$

$ unexpand -a file2 > file3

$ cat -vet file3
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$
One^ITwo^IThree^IFour^IFive^Isix^Iseven$

Expand Command Options:


       -a, --all
              convert all blanks, instead of just initial blanks

       --first-only
              convert only leading sequences of blanks (overrides -a)

       -t, --tabs=N
              have tabs N characters apart instead of 8 (enables -a)

       -t, --tabs=LIST
              use comma separated LIST of tab positions (enables -a)

       --help display this help and exit

       --version
              output version information and exit