Introduction to sed

sed is a stream editor. It is used to perform basic text transformation.

Syntax

sed SCRIPT INPUTFILE

Substitution

Replace first occurrence in each the lines with new value

sed 's/<OLD_VALUE>/<NEW_VALUE>/' <INPUT_FILE>

Example

To replace first occurrences of ‘pandian’ to ‘satheesh’ in each lines in the file input.txt

Output

pandian is replaced by satheesh in each line ONLY in the first occurrence. If you see the input snapshot, third line has pandian in two places. The sed command just replaces in the first occurrence. In the second occurrence, it is still showing pandian.

Replace n^th occurrence in each line with new value

sed 's/<OLD_VALUE>/<NEW_VALUE>/<OCCURRENCE_NUMNBER>' <INPUT_FILE>

Example

To replace specific occurrence of ‘pandian’ to ‘satheesh’ in each lines in the file input.txt

Output

pandian is replaced by satheesh in each line ONLY in the second occurrence. If you see the input snapshot, third line has pandian in two places. The sed command just replaces in the second occurrence. In the fist occurrence, it is still showing pandian and also other lines still show pandian in the first occurrence.

Replace all occurrences in entire file with new value

sed 's/<OLD_VALUE>/<NEW_VALUE>/g' <INPUT_FILE>

Example

To replace all occurrences of ‘pandian’ to ‘satheesh’ in the file input.txt

Output

pandian is replaced by satheesh in every single place in the file.

Replace from n^th occurrences in each line with new value

sed 's/<OLD_VALUE>/<NEW_VALUE>/<OCCURRENCE_NUMNBER>g' <INPUT_FILE>

Example

To replace 2nd occurrences onwards of ‘pandian’ to ‘satheesh’ in each of the file input.txt

Output

pandian is replaced by satheesh from 2nd occurrence in each line. If you look at first two lines, there is only ONE pandian value. Hence, these lines are not impacted. However, if you look at third and fourth lines, pandian occurrences more than once. Hence, from second occurrence onwards, pandian is replaced by satheesh.

Replace the first occurrences in specific line with new value

sed '<OCCURRENCE_NUMNBER> s/<OLD_VALUE>/<NEW_VALUE>/' <INPUT_FILE>

Example

To replace first occurrences of ‘pandian’ to ‘satheesh’ in third line of the file input.txt

Output

First occurrence of pandian is replaced by satheesh in the third line and NO OTHER CHANGE in the file.

Replace from n^th occurrences onwards in specific line with new value

sed '<OCCURRENCE_NUMNBER> s/<OLD_VALUE>/<NEW_VALUE>/g' <INPUT_FILE>

Example

To replace second occurrences onwards of ‘pandian’ to ‘satheesh’ in fourth line of the file input.txt

Output

Second occurrences onwards of pandian is replaced by satheesh in the fourth line and NO OTHER CHANGE in the file.

Replace all the occurrences in specific line with new value

sed '<OCCURRENCE_NUMNBER> s/<OLD_VALUE>/<NEW_VALUE>/g' <INPUT_FILE>

Example

To replace all the occurrences of ‘pandian’ to ‘satheesh’ in third line of the file input.txt

Output All the occurrence of pandian is replaced by satheesh in the third line and NO OTHER CHANGE in the file.