What is sed?
sed is a “stream editor for filtering and transforming text”. Here is a very detailed tutorial.
Basic usages
Use “s” for substitution
Basic syntax:
echo "Sunday Monday" | sed 's/day/night/'
Sunnight Monday
Note that only the first occurrence of day was replaced by night. To replace all, you have to use sed pattern flag /g for global replacement.
echo "Sunday Monday" | sed 's/day/night/g'
Sunnight Monnight
Flexible delimiters
I think we all agree that the following code is ugly:
echo "/usr/local/bin/n" | sed 's/\/usr\/local/\/usr/'
With sed, the delimiter does not need to be /. It can be /, _, -, #, * etc. Pick the one fit you the best.
echo "/usr/local/bin/n" | sed 's_/usr/local_/usr_'
echo "/usr/local/bin/n" | sed 's-/usr/local-/usr-'
echo "/usr/local/bin/n" | sed 's#/usr/local#/usr#'
echo "/usr/local/bin/n" | sed 's*/usr/local*/usr*'
echo "/usr/local/bin/n" | sed 's</usr/local</usr<'
# ...