Day 54: Basic replaces with sed

26 Sep 2017

One of the most powerful unix/linux command for parsing is sed.

The “find and replace” command has the following syntax:

sed 's/<before>/<after>' <file>

Find and replace:

$ cat foobar.txt
foobar
barfoo

$ sed 's/foobar/barfoo/' foobar.txt
barfoo
barfoo

Separator

The / separator is very popular on internet, but do you know that any char can be used as separator ?

$ sed 's#foobar#barfoo#' foobar.txt
barfoo
barfoo

$ sed 's?foobar?barfoo?' foobar.txt
barfoo
barfoo

Multiple occurencies

Just add g at the end of the sed command:

$ sed 's/bar/424242/' foobar.txt
foo424242
barfoo

$ sed 's/bar/424242/g' foobar.txt
foo424242
424242foo

Write changes on disk

This can be done with -i argument:

# override foobar.txt
$ sed -i 's/foobar/barfoo/' foobar.txt

$ cat foobar.txt
barfoo
barfoo

# override foobar.txt and backup previous file
$ sed -i.bak 's/foobar/barfoo/' foobar.txt

$ cat foobar.txt
barfoo
barfoo

$ cat foobar.txt.bak
foobar
barfoo