Summary

sed is a stream editor. A stream editor is used to perform basic text transformations on an input stream (a file or input from a pipeline). While in some ways similar to an editor which permits scripted edits (such as ed), sed works by making only one pass over the input(s), and is consequently more efficient. But it is sed’s ability to filter text in a pipeline which particularly distinguishes it from other types of editors.

Usage

Delete a line from file

sed -e '/<pattern>/d' -i <input file>"

Commenting or uncommenting a pattern matched line

sed -e '/<pattern>/s/^/#/g' -i <input file> # (to comment out)
sed -e '/<pattern>/s/^#//g' -i <input file> # (to uncomment)

Examples

Deleting a line from a file

Below is an ls of the test file’s directory and its file content. The file has four lines, and the third line should be removed from the file. This file is very important and may require a rollback. To ensure a backup is made, to ease the rollback process, an extra option, -i<SUFFIX>, will be utilized. The extra option allows editing the file in place, and creates a backup file in case a rollback is required.

ls
test

cat test
This is my first line
This is my second line
This is my third line - delete me
This is my last line

sed -e '/delete me/d' -i.backup test

Below is an ls of the test file’s directory and its file content after the line has been removed, and a diff of the edited and backup file.

ls
test  test.backup

cat test
This is my first line
This is my second line
This is my last line

diff test test.backup
2a3
> This is my third line - delete me

Referenced commands: cat, diff, ed, ls