Linux Commands

Understanding sed Command

August 14, 2020
3 Min Read
Understanding sed Command
Understanding sed Command

Understanding sed Command

This post helps Understanding sed Command. sed command stands for stream editor and is used to search, find and replace, insert or delete a string. Generally, it is used to replace a particular pattern or text in a file. In short, we can edit files even without opening it using sed command.

sed 's/place/city/' newfile.txt

In the above example, sed command replaces the word “place” with “city” in the file “newfile.txt”.

Here “place” is the search pattern, “city” is the replacement string and ‘/’ is the delimiter. By default, sed command replaces only the first occurrence of the pattern in each line

Replace nth occurrence of a pattern:

If you want to replace only the second occurrence of a pattern or only the third occurrence of a pattern in a line, you can use the following command:

sed 's/place/city/2' newfile.txt

or

sed 's/place/city/3' newfile.txt

Replace all the occurrence of a pattern:

If you want to replace all the occurrences of a pattern in a line:

sed 's/place/city/g' newfile.txt

Replace from nth occurrence to all occurrences:

If you want to replace all the patterns from the 3rd occurrence to all the subsequent occurrences in a line:

sed 's/place/city/3g' newfile.txt

Replace the string on a specific line:

To replace the string ‘place’ only on line 3 with ‘city’:

sed '3 s/place/city/' newfile.txt

Duplicate the line which has the search pattern:

To duplicate all the lines which have the search pattern use the /p flag:

sed 's/place/city/p' newfile.txt

Print only the replaced lines:

Use -n option along with /p flag to suppress the duplicate lines and print only the replaced lines.

sed -n 's/place/city/p' newfile.txt

Replace string on a range of lines:

sed '1,3 s/place/city/' newfile.txt

Here the string will be replaced from line 1 to line 3

sed '3,$ s/place/city/' newfile.txt

‘$’ sign indicates the last line.

The string will be replaced from 3rd to the last line.

Delete lines from a file:

To delete nth line from newfile.txt

sed 'nd' newfile.txt

To delete the last line.

sed '$d' newfile.txt

To delete a range of lines from p to t

sed 'p,td' newfile.txt

To delete the lines which have the specified pattern.

sed '/pattern/d' newfile.txt

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