Sed

Oct 31, 2020 / Updated on Oct 31, 2020

SED: Delete lines from file (delete command)



SED: Extract specific lines from a file (print command)

To extract line 3 and 5

sed -n -e '3p' -e '5p' my.txt

or semi colon separated

sed -n -e '3p;5p' my.txt

Extract range of lines - e.g. get lines from 2 to 5

sed -n -e '2,5 p' my.txt

Extract last line of the file

sed -n -e '$ p' my.txt

Extract range of lines: from 3 to last line

sed -n -e '3,$ p' my.txt 

Extract no. of lines from a specific line. e.g. get four lines starting from line 2

sed -n -e '2,+4 p' my.txt 

Extract every nth line starting form a specific line. e.g. get every 2nd line starting from first line

send -n -e '1~2 p' my.txt

Extract lines containing specific word. e.g. lines containing the word rocket

sed -n -e '/rocket/ p' my.txt

Extracts lines starting with first match of rocket to the nth line

sed -n -e '/rocket/, 5 p' my.txt # till 5th line
sed -n -e '/rocket/, $ p' my.txt # till last line
sed -n -e '/rocket/, +5 p' my.txt # next 5 lines after the match

Lines between two words

sed -n -e '/rocket/, /science/ p' my.txt

SED: Extract and write to file (write command)

This one exactly same as p command described above, except here we give a filename and output is written to the file.

e.g. to extract all lines containing the word rocket into a file rocket.txt

sed -n -e '/rocket/ w rocket.txt' my.txt

interestingly, following writes each patterns into separate file. i.e. lines containing rocket written into rocket.txt and lines containing the word science are written into science.txt

sed -n -e '/rocket/ w rocket.txt' -e '/science/ w science.txt' my.txt

SED: Append command

Append a line after nth line e..g insert a new line ‘this is some line’ after 4th line

sed -e '4 a this is some line' my.txt

Insert after the last line

send -e '$ a this is some line' my.txt

Insert after specific pattern (Note: inserted for each match)

send -e '/rocket/ a this is some line' my.txt

SED: Insert command

Insert command works same way as append command mentioned above, the only difference it inserts before the line

SED: Read command

Read command similar to append except it get the contents from file

Append content from file after nth line e..g insert the content of my2.txt after 4th line of my.txt

sed -e '4 r my2.txt' my.txt

SED: Change command

Replace a line with new line e.g. replace line 3 with ‘this is new line’

sed -e '3 c this is new line' my.txt

Replace a line containing word

sed -e '/rocket/ c this is new line' my.txt

Replace range of lines e.g. replace lines 2 to 4 with ‘this is new line’

sed '4, 6 c this is new line' my.txt

SED: Translate command

Translate characters

echo 'this is some text' | sed 'y/abcdefghij/1234567890/'

this outputs t89s 9s som5 t5xt

SED L command

Replace white space with escape chars

sed -n 'l' my.txt

this command replaces tab with \t and end of line with $, etc

To wrap lines with n chars

send -n -e 'l 5' my.txt

SED: quit command

Print first 3 lines

sed -e '3 q' my.txt

print until pattern match

sed -e '/rocket/ q' my.txt

quit with exit status e.g. exit with status code 1

sed -e '/rocket/ q 11' my.txt

after executing the above check the status echo $? this prints 11

SED: Execute command

Executes external command

e.g. insert date at line 3

sed '3 e date' my.txt

insert data where it matches a word

sed '/rocket/ e date' my.txt

SED: = command

The = command writes the line number followed by its contents

sed '=' my.txt 

Line number for first 3 lines

sed '1, 3=' my.txt 

SED: & command

& gives the matched pattern value

e.g following replaces science with rocket science

sed 's/science/rocket &/' my.txt

SED: Substitute command

Replace a pattern with a value

e.g. change first occurrences of rocket with science in each line.

sed -e 's/rocket/science/' my.txt

on all occurrences

sed -e 's/rocket/science/g' my.txt

restrict by pattern. e.g. replace rocket with science where a line contains the word extreme

sed -e '/extreme/ s/rocket/science/g' my.txt

Replace the second occurrence

sed -e '/s/rocket/science/2' my.txt

print only changed lines

sed -e '/s/rocket/science/p' my.txt

Write only changed lines to a different file

sed -e '/s/rocket/science/w new.txt' my.txt

SED: command index

  • a = append
  • b = branch
  • c = change text
  • d = delete lines
  • D = delete first line (in patspace)
  • e = execute on the command line
  • g = copy from holdspace
  • G = append from hold space
  • h = copy to hold space
  • H = append to hold space
  • i = insert
  • l = print substitute line feeds
  • n = next input line
  • N = append next input line
  • p = print
  • P = print first line
  • q = quit
  • Q = quit immediately
  • r = read file
  • R = read line from file
  • s = substitute
  • t = test for substitution
  • T = test for no substitution
  • y = simple character replace
  • w = write to file
  • W = write line to file
  • z = clear line (zap)
  • = = print line number

SED: Options

-n, –quiet, –silent: Same as standard -n option.

-e script, –expression=script: Same as standard -e option.

-f script-file, –file=script-file: Same as standard -f option.

--follow-symlinks: If this option is provided, the SED follows symbolic links while editing files in place.

-i[SUFFIX], –in-place[=SUFFIX]: This option is used to edit file in place. If suffix is provided, it takes a backup of the original file, otherwise it overwrites the original file.

-l N, –line-lenght=N: This option sets the line length for l command to N characters.

--posix: This option disables all GNU extensions.

-r, –regexp-extended: This option allows to use extended regular expressions rather than basic regular expressions.

-u, –unbuffered: When this option is provided, the SED loads minimal amount of data from the input files and flushes the output buffers more often. It is useful for editing the output of “tail -f” when you do not want to wait for the output.

-z, –null-data: By default, the SED separates each line by a new-line character. If NULL-data option is provided, it separates the lines by NULL characters.

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