Kyle Brandt

Update: David Harding pointed out in his comment to this post that the column utility does exactly this. Therefore, the following is really just an academic exercise.

In my last post I showed how to get columns outputted in the command line to line up using python. In this post I am going to show you how to do it with Bash scripts (I think you could also use this same method with python using calls to the shell). Instead of padding the columns with spaces as I did in my previous post, this time we use a tab character for the delimiter and manually set the tab stops in the terminal itself. Since this is the terminal, not the shell, this will work with other shells as well (such as my favorite interactive shell, Zsh).

There is example code at the bottom. Instead of creating functions as I did with my previous post I have kept this example pretty tedious (repetitive code etc) to lessen the levels of abstraction and make the example a little clearer.

The first part finds the max width of each column of a text file. This example has 4 columns and a while loop that splits them on the tab character by setting the IFS ( Input Field Separator ) variable to tab for the loop only. Each iteration of the while loop remembers the value of each column; it saves the value in the $max# variable if the length was larger then the previous iteration ( the variable substitution ${#variable} returns the length of the variable ).

The second part, after the while loop, finds where the tab stops should be placed. The setterm command with the -tabs switch sets tab stops at absolute positions up to 160 ( each argument specifies where the tab stop is relative to the start of the line, not relative to the previous tab stop ) . So for this example, the second tab stop position is found by adding the width of the first column to the width of second column — this gives us the position relative to the start of line. Lastly, after setting the tab stops the file is displayed on the terminal with cat.

A caveat is that it is hard to find out what to set $TERM to. On my machine, when I am in screen session $TERM is equal to ’screen’, but this doesn’t work with setterm, I have to set TERM to ‘linux’.

I hope this helps someone when creating their next command line utility that uses columns.