Sed, short for Stream EDitor, is a command that is used to perform text transformations and manipulations on a file. Some of these transformations include searching and replacing text. With Linux sed command, you can manipulate and edit text files without even opening them. In this tutorial, you will learn how to manipulate text files using sed command.
Linux sed command syntax
$ sed {OPTIONS} filenameIn this tutorial, we will be using linuxgeek.txt file as our reference file.
# cat linuxgeek.txtOutput
1. Substituting or replacing a string
In most cases, sed command is used for replacing strings of text.
The command below replaces ‘Linux‘ with ‘Unix‘.
# sed 's/Linux/Unix/' linuxgeek.txt- The
sin the command is the replacement indicator. - The
/are the delimiters Linuxis the search termunixis the replacement term
By default, sed command replaces only the first occurrence in a line. The subsequent occurrences will not be substituted or replaced.
Output
2. Substituting or replacing the nth occurrence in a line
If you want to replace the second string occurrence in a line, use the /2 flag as shown.
# sed 's/Linux/Unix/2' linuxgeek.txtOutput
3. Substituing or replacing all occurrences of the pattern in a file
To replace all the occurrences of the search pattern in the file, use the /g flag. The /g is the global replacement.
# sed 's/Linux/Unix/g' linuxgeek.txtOutput
4. Substituting or replacing all occurrences of a string in a specific line only
If you want to replace all occurrences of a string in a specific line, say in line 2, use the syntax below
# sed '2 s/Linux/Unix/g' linuxgeek.txtOutput
5. Substituting or replacing a string in a specific range of lines
If you want to specify the range of lines that the string replacement will occur, use the example shown below. The example instructs the replacement to occur from lines 1 -3
# sed '1,3 s/Linux/Unix/g' linuxgeek.txtOutput
Additionally, you can replace text from a specific line to the end of the file as shown
# sed '2,$ s/Linux/Unix/g' linuxgeek.txtWhat the command does is that it replaces all the occurrences from the 2nd line to the last line of the file.
6. Parenthesize the first character of every word
The example below demonstrates how you can put parenthesis on every first character of a word in a line.
$ echo "Hey Guys, Welcome To Linux Operating System" | sed 's/(b[A-Z])/(1)/g'
Output
7. Delete lines from a file
You can also use the linux sed command to delete lines in a file.
Examples
Syntax:
$ sed 'nd' filename.txt
To delete the 3rd line in the file execute
$ sed '3d' linuxgeek.txtOutput
To delete a range of lines, say from line 3 to line 5 , run the command:
$ sed '3,5d' linuxgeek.txtOutput
