The unexpand command can be used to change a file to be separated with tabs instead of spaces, and the expand command can be used to change a file to be separated with spaces instead of tabs. In this example, each word in file 1 is separated by a single space.

[root@server1 ]# cat file1
Hello world
How are you today?

The unexpand command with the -t or --tabs option can be used to change a space into a tab. In this example, file1 is not changed because the unexpand command will only convert strings consisting of at least two spaces.

[root@server1 ]# unexpand --tabs=1 file1
Hello world
How are you today?

Let's take an example where file2 has words separated by at least 2 spaces.

[root@server1 ]# cat file2
Hello  world
How  are  you  today?

The unexpand command with the -t or --tabs option will now place a tab (8 spaces) between each word.

[root@server1 ]# unexpand --tabs=1 new-file1
Hello        world
How        are        you        today?

The cat command with the -T or --show-tabs and -e (show line feed) options can be used to be absolutely certain that file1 is delimited with tabs. The ^I character represents a tab and $ represents a line feed.

[root@server1 ]# cat -te file1
Hello^Iworld$
How^Iare^Iyou^Itoday?$