Bash: Update a variable within a file

Question

I know this is a simple answer and I could probably keep digging around on Google before I stroll across the answer. But I am on a tight schedule and I was hoping for an easy re

Answer 1

You can make use of something like this, which lets you define exactly what values you want to add in the file:

$ bootproto="static"
$ sed -r "s/(BOOTPROTO\s*=\s*).*/\1$bootproto/" file
ONBOOT=no
BOOTPROTO=static

And to make the two of them together:

$ onboot="yes"
$ bootproto="static"
$ sed -r -e "s/(ONBOOT\s*=\s*).*/\1$onboot/" -e "s/(BOOTPROTO\s*=\s*).*/\1$bootproto/" file
ONBOOT=yes
BOOTPROTO=static

Explanation

• (BOOTPROTO\s*=\s*).* catches a group of text containing BOOTPROTO + any_number_of_spaces + = + any_number_of_spaces. Then, matches the rest of the text, that we want to remove. \1$var prints it back together with the given variable.
• \s* keeps the current spaces as they were and then replaces the same line changing the current text with the bash variable $bootproto.
• -r is used to catch groups with () instead of \( and \).

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To make it edit in place, use sed -i.bak. This will create a backup of the file, file.bak, and the file will be updated with the new content.

All together:

sed -ir -e "s/(ONBOOT\s*=\s*).*/\1$onboot/" -e "s/(BOOTPROTO\s*=\s*).*/\1$bootproto/" file