sed command and its commonly usage

Table of contents

1. Introduction
2. Various ways of using sed
3. Repeated patterns
   1. print lines
   2. Insert and Append
   3. delete lines
   4. comment/uncommend
   5. change variable value
   6. convert CRLF to LF
   7. substitute first or last in file
   8. substitute if pattern
4. Resources

Introduction

sed is a powerful stream editor that allows you to perform text transformations on input streams or files. It is commonly used in Bash scripts for tasks like search and replace, text substitution, and pattern matching.

Various ways of using sed

# multi command
echo "hello world" | sed -e 's/hello/Hello/g' -e 's/world/Stream EDitor/g'

# read patterns from sed file
echo 's/hello/Hello/g' >> hello.sed
echo 's/world/Stream EDitor/g' >> hello.sed
echo "hello world" | sed -f hello.sed
Hello World

# create backup befor any change
echo "hello world" > hello.txt
sed 's/world/sed/g' -i.bk hello.txt

# inline change without backup
sed 's/world/sed/g' -i hello.txt

Repeated patterns

print lines

sed -n '1,10p' input_file

This command prints lines 1 to 10 from the input file. The -n flag suppresses automatic printing, and the p command explicitly prints the specified range of lines.

Insert and Append

sed '2i\This is a new line' input_file

This command inserts "This is a new line" before line 2 in the input file. The i command is used for inserting text at a specified line number. Similarly, you can use the a command to append text after a specific line.

delete lines

# delete the last line of a file
sed '$d'

# delete the first 5 lines of a file
sed '1,5d'

# delete from the 10th line to the last line of a file
sed '10,$d'

# delete ALL lines matched pattern from a file
sed '/pattern/d'

# delete ALL blank lines from a file
sed '/^$/d'

# delete all leading blank lines at top of file
sed '/./,$!d'

# delete all trailing blank lines at end of file
sed -e :a -e '/^\n*$/{$d;N;ba' -e '}'  # works on all seds

comment/uncommend

sed '/<pattern>/s/^/#/g'           # (to comment out)

sed '/<pattern>/s/^#//g'           # (to uncomment)

sed '3,5s/^#//'                    # (to uncomment lines between 3 and 5)

change variable value

sed 's/var=.*/var=new_value/'

convert CRLF to LF

# DOS/Windows to Unix
sed 's/\r$//'

# Unix to DOS/Windows
sed 's/$/\r/'

substitute first or last in file

# substitute first
sed '1 s/foo/bar/g'

# substitute last
sed '$s/foo/bar/g'

substitute if pattern

# substitute if pattern matched
sed '/pattern/ s/foo/bar/g'

# substitute if pattern not matched
sed '/pattern/! s/foo/bar/g'

Resources

sed1line

catonmat sed.stream.editor.cheat.sheet

au-bio-bootcamp cheatsheet_sed

eriklievaart sed

Doing cut and paste with sed

lzone cheat-sheet/sed

quickref sed

Linuxhint - 50 sed command example