Change tab size of “cat” command

Question

When I am in vim I can change the tab size with the following command:

:set ts=4

Is it possible to set tab size for cat command output too?

Answer 1

The first command here emulates the formatting you see in vim. It intelligently expands tabs to the equivalent number of spaces, based on a tab-STOP (ts) setting of every 4 columns.

printf "ab\tcd\tde\n" |expand -t4   

Output

ab  cd  de

To keep the tabs as tabs and have the tab STOP positions set to every 4th column, then you must change the way the environment works with a tab-char (just as vim does with the :set ts=4 command)

For example, in the terminal, you can set the tab STOP to 4 with this command;

tabs 4; printf "ab\tcd\tde\n" 

Output

ab  cd  de

Answer 2

There's no notion of tabs or tab stops in cat; the program just funnels the inputs to the output and treats tabs like any other character. If the output device happens to be a terminal, tabs will be handled according to whatever behavior the terminal is configured to provide.

Systems implementing POSIX.1 have a command called tabs(1) that will adjust the terminal's concept of how tabs should be displayed. Depending on a particular tab layout is not considered a good idea, as someone may send your file to some other device such as a printer that won't do what you intended.

When you adjust ts in vim (or plain vi), all you're doing is adjusting how the editor interprets tab characters when displayed. It has no bearing on what ends up in the file.

Answer 3

According to the manpage, cat can not do it on its own. But you can e.g. run the output from cat through tr filter to replace the tabs with any number of spaces you wish:

cat somefile | tr '\t' '  '

will replace the tab character with two spaces.

Update: as pointed out in the comments to this post, this actually does not work. Nevertheless, I'm keeping the answer as an example of how not to do it.