sed

sed linux command cheatsheet by Thamizhiniyan C S

Introduction

Sed is a Stream Editor used for modifying the files in unix (or linux).

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Syntax

sed [flags] [pattern/script] [input file]

'[condition(s)(optional)] [command/mode(optional)]/[source/to-be-searched pattern(mandatory)]/[to-be-replaced pattern(depends on command/mode you use)]/[args/flags to operate on the pattern searched(optional)]'

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Important Flags

Flags	Description
-e	To add a script/command that needs to be executed with the pattern/script(on searching for pattern)
-f	Specify the file containing string pattern
-E	Use extended regular expressions
-n	Suppress the automatic printing or pattern spacing

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Modes / Commands

Commands	Description
s	(Most used)Substitute mode (find and replace mode)
y	Works same as substitution; the only difference is, it works on individual bytes in the string provided(this mode takes no arguments/conditions)

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Arguments

Flags/Args	Description
/g	globally(any pattern change will be affected globally, i.e. throughout the text; generally works with s mode)
/i	To make the pattern search case-insensitive(can be combined with other flags)
/d	To delete the pattern found(Deletes the whole line; takes no parameter like conditions/modes/to-be-replaced string)
/p	prints the matching pattern(a duplicate will occur in output if not suppressed with -n flag.)
/1,/2,/3../n	To perform an operation on an nth occurrence in a line(works with s mode)

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Examples

Command	Description
sed 's/unix/linux/' file.txt	Replacing or substituting string
sed 's/unix/linux/2' file.txt	Replacing the nth occurrence of a pattern in a line
sed 's/unix/linux/g' file.txt	Replacing all the occurrence of the pattern in a line
sed 's/unix/linux/3g' file.txt	Replacing from nth occurrence to all occurrences in a line
sed 's_http://_www_' file.txt	Changing the slash (/ -> _) delimiter
sed 's/unix/{&}/' file.txt	Using & as the matched string ( adding curly braises )
sed 's/(unix)/11/' file.txt	Replace the word “unix” in a line with twice as the word like “unixunix”
sed 's/(unix)(linux)/21/' file.txt	Switch the words “unixlinux” as “linuxunix”
sed 's/^(.)(.)(.)/321/' file.txt	Switching the first three characters in a line
sed 's/unix/linux/p' file.txt	Duplicating the replaced line with /p flag
sed -n 's/unix/linux/p' file.txt	Printing only the replaced lines
sed 's/unix/linux/' file.txt | sed 's/os/system/'	Run multiple sed commands by piping the output of one sed command as input to another sed command
sed -e 's/unix/linux/' -e 's/os/system/' file.txt	To run multiple sed commands in a single sed command
sed '3 s/unix/linux/' file.txt	Replacing string on a specific line number
sed '1,3 s/unix/linux/' file.txt	Replacing string on a range of lines
sed '2,$ s/unix/linux/' file.txt	Replacing the text from second line to last line in the file
sed '/linux/ s/unix/centos/' file.txt	Replace on a lines which matches a pattern. Here the sed command first looks for the lines which has the pattern “linux” and then replaces the word “unix” with “centos”
sed '2 d' file.txt	Deleting lines
sed 'p' file.txt	Duplicating lines
sed -n '/unix/ p' file.txt	Sed as grep command
sed '/unix/ a "Add a new line"' file.txt	Add a line after a match
sed '/unix/ i "Add a new line"' file.txt	Add a line before a match
sed '/unix/ c "Change line"' file.txt	Change a line
sed 'y/ul/UL/' file.txt	Transform like tr command
sed 's/\bthe\b/this/'	Transform the first occurrence of the word 'the' with 'this' in each line
sed 's/\bthy\b/your/Ig'	Case Insensitive transform all the occurrences of the word 'thy' with 'your'
sed 's/thy/{&}/Ig'	Case Insensitive. Highlight all the occurrences of 'thy' by wrapping them up in brace brackets
sed 's/\(\d\{4\}\s\)\{2\}\(\d\{4\}\)/**** **** ****/g'	Replace occurrences of credit card numbers in the format XXXX XXXX XXXX with a masked version **** **** **** in each line
sed -E 's/([0-9]+) ([0-9]+) ([0-9]+) ([0-9]+)/\4 \3 \2 \1/'	Rearranges these groups in reverse order, separated by whitespace, effectively reversing the order of the groups of digits in each line
sed 's/hack/back/3' file.txt	Substitute every 3rd occurrence of the word 'hack' to 'back' on every line
sed '3,4 s/hack/back/3' file.txt	Substitute every 3rd occurrence of the word 'hack' to 'back' on 3rd and 4th line
sed 's/ */:/g' sed1.txt	Formatting the trailing spaces in sed1.txt with a colon(:)
sed 's/\(^\b[[:alpha:] ]*\)\([[:digit:]]*\)/\=\> \1\[\2\]/g' file.txt	Making every line to start with a bullet point and enclose the digits in square brackets using regex
sed -e 's/[[:digit:]]//g' -e 's/ *//'g sed2.txt	Remove all digits and replace trailing spaces into a single space