How to left justify text in Bash

Question

Given a text, $txt, how could I left justify it to a given width in Bash?

Example (width = 10):

If $txt=hello, I would like to print:

hello     |

If $txt=1234567890, I would like to print:

1234567890|

Answer 1

You can use the printf command, like this:

printf "%-10s |\n" "$txt"

The %s means to interpret the argument as string, and the -10 tells it to left justify to width 10 (negative numbers mean left justify while positive numbers justify to the right). The \n is required to print a newline, since printf doesn't add one implicitly.

Note that man printf briefly describes this command, but the full format documentation can be found in the C function man page in man 3 printf.

Answer 2

Bash contains a printf builtin:

txt=1234567890
printf "%-10s\n" "$txt"

Answer 3

You can use the - flag for left justification.

Example:

[jaypal:~] printf "%10s\n" $txt
     hello
[jaypal:~] printf "%-10s\n" $txt
hello