Find and replace with SED

Published 7 december, 2015 | By Tuncay Sahin

Linux Sed command is a stream editor that can perform basic text transformation on input stream. It can be used for editing in shell scripts for non-interactive editing. Sed can be used to find and replace a pattern on the input.

Examples

The syntax of the command is:

sed ‘s/ //’

echo “Hello there” | sed -e ‘s/there/here/’

Output is: Hello here

Replaces just first instance of pattern in a line. Here, 2 instances of ‘one’ exist in the file. But sed has replaced only the first one	cat numbers.txt one two three one sed -i ‘s/one/four/’ numbers.txt four two three one
Replace all the instances of the pattern, with the ‘g’ command of sed:	sed -i ‘s/one/four/g’ numbers.txt four two three four
Replace all the instances of the pattern for multiple files within a folder	find /home/private -type f -exec sed -i ‘s/one/four/g’ {} \;
Example script	#!/bin/bash for fl in *.php; do mv $fl $fl.old sed ‘s/FINDSTRING/REPLACESTRING/g’ $fl.old > $fl rm -f $fl.old done

Insert and Append

A pattern can be inserted to the file with ‘i’ command and appended with ‘a’ command. This insert and append operation use a newline for inserting and appending.

Insert a new line above	sed ‘i \inserted line’ numbers.txt
Append a new line at the end	sed ‘a \Appended line’ numbers.txt
Suppress the output by running sed in quiet mode.	sed -n ‘s/one/four/’ numbers.txt
Printing the output	sed -n ‘s/one/four/p’ numbers.txt
Find the pattern (like grep) root in the file /etc/passwd.	sed -n ‘/root/p’ /etc/passwd root:x:0:0:root:/root:/bin/bash
Deleting lines 1 to 3 from the given file.	sed ‘1,3d’ count.txt
Writing to a file	sed -n ‘/root/w rootpwd.txt’ /etc/passwd

Posted in ICT Knowledgebase, Linux (RHEL / CentOS)

Tuncay Sahin

ICT Engineer | Docent ICT & Trainer

Find and replace with SED

Examples

Insert and Append

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