Text slicing and parameter operations

This recipe walks through some simple text-replacement techniques and parameter-expansion shorthands available in Bash. A few simple techniques can help avoid writing multiple lines of code.

How to do it...

Let's get into the tasks.

Replace some text from a variable:

$ var="This is a line of text"
    $ echo ${var/line/REPLACED}
    This is a REPLACED of text"

The line word is replaced with REPLACED.

We can produce a substring by specifying the start position and string length, using the following syntax:

${variable_name:start_position:length}

Print from the fifth character onwards:

$ string=abcdefghijklmnopqrstuvwxyz
    $ echo ${string:4}
    efghijklmnopqrstuvwxyz

Print eight characters starting from the fifth character:

$ echo ${string:4:8}
    efghijkl

The first character in a string is at position 0. We can count from the last letter as -1. When -1 is inside a parenthesis, (-1) is the index for the last letter:

echo ${string:(-1)}
    z
    $ echo ${string...