sed - 25 examples to delete a line or pattern in a file

In this article of  sed tutorial series, we are going to see how to delete or remove a particular line or a particular pattern from a file using the sed command.

 Let us consider a file with the sample contents as below:

$ cat file
Cygwin
Unix
Linux
Solaris
AIX

1. Delete the 1st line or the header line:

$ sed '1d' file
Unix
Linux
Solaris
AIX

      d command is to delete a line. 1d means to delete the first line.

     The above command will show the file content by deleting the first line. However, the source file remains unchanged. To update the original file itself with this deletion or to make the changes permanently in the source file, use the -i option. The same is applicable for all the other examples.

sed -i '1d' file

    Note: -i option in sed is available only if it is GNU sed. If not GNU, re-direct the sed output to a file, and rename the output file to the original file.

2. Delete a particular line, 3rd line in this case:

$ sed '3d' file
Cygwin
Unix
Solaris
AIX

3. Delete the last line or the trailer line of the file:

$ sed '$d' file
Cygwin
Unix
Linux
Solaris

       $ indicates the last line.

4. Delete a range of lines, from 2nd line till 4th line:

$ sed '2,4d' file
Cygwin
AIX

       The range is specified using the comma operator.

5. Delete lines other than the specified range, line other than 2nd till 4th here:

$ sed '2,4!d' file
Unix
Linux
Solaris

       The ! operator indicates negative condition.

6. Delete the first line AND the last line of a file, i.e, the header and trailer line of a file.

$ sed '1d;$d' file
Unix
Linux
Solaris

     Multiple conditions are separated using the ';' operator. Similarly, say to delete 2nd and 4th line, you can use: '2d;3d'.

7. Delete all lines beginning with a particular character, 'L' in this case:

$ sed '/^L/d' file
Cygwin
Unix
Solaris
AIX

      '^L' indicates lines beginning with L.

8. Delete all lines ending with a particular character, 'x' in this case:

$ sed '/x$/d' file
Cygwin
Solaris
AIX

      'x$' indicates lines ending with 'x'. AIX did not get deleted because the X is capital.

9. Delete all lines ending with either x or X,  i.e case-insensitive delete:

$ sed '/[xX]$/d' file
Cygwin
Solaris

    [xX] indicates either 'x' or 'X'. So, this will delete all lines ending with either small 'x' or capital 'X'.

10. Delete all blank lines in the file

$ sed '/^$/d' file
Cygwin
Unix
Linux
Solaris
AIX

      '^$' indicates lines containing nothing and hence the empty lines get deleted. However, this wont delete lines containing only some blank spaces.

11. Delete all lines which are empty or which contains just some blank spaces:

$ sed '/^ *$/d' file
Cygwin
Unix
Linux
Solaris
AIX

      '*' indicates 0 or more occurrences of the previous character. '^ *$' indicates a line containing zero or more spaces. Hence, this will delete all lines which are either empty or lines with only some blank spaces.

12. Delete all lines which are entirely in capital letters:

$ sed '/^[A-Z]*$/d' file
Cygwin
Unix
Linux
Solaris

      [A-Z] indicates any character matching the alphabets in capital.

13. Delete the lines containing the pattern 'Unix'.

$ sed '/Unix/d' file
Cygwin
Linux
Solaris
AIX

     The pattern is specified within a pair of slashes.

14. Delete the lines NOT containing the pattern 'Unix':

$ sed '/Unix/!d' file
Unix

15. Delete the lines containing the pattern 'Unix' OR 'Linux':

$ sed '/Unix\|Linux/d' file
Cygwin
Solaris
AIX

     The OR condition is specified using the | operator. In order not to get the pipe(|) interpreted as a literal, it is escaped using a backslash.

16. Delete the lines starting from the 1st line till encountering the pattern 'Linux':

$ sed '1,/Linux/d' file
Solaris
AIX

    Earlier, we saw how to delete a range of lines. Range can be in many combinations: Line ranges, pattern ranges, line and pattern, pattern and line.

17. Delete the lines starting from the pattern 'Linux' till the last line:

$ sed '/Linux/,$d' file
Cygwin
Unix

18. Delete the last line ONLY if it contains the pattern 'AIX':

$ sed '${/AIX/d;}' file
Cygwin
Unix
Linux
Solaris

      $ is for the last line. To delete a particular line only if it contains the pattern AIX, put the line number in place of the $. This is how we can implement the 'if' condition in sed.

19. Delete the last line ONLY if it contains either the pattern 'AIX' or 'HPUX':

$ sed '${/AIX\|HPUX/d;}' file
Cygwin
Unix
Linux
Solaris

20. Delete the lines containing the pattern 'Solaris' only if it is present in the lines from 1 to 4.

$ sed '1,4{/Solaris/d;}' file
Cygwin
Unix
Linux
AIX

      This will only delete the lines containing the pattern Solaris only if it is in the 1st four lines, nowhere else.

21. Delete the line containing the pattern 'Unix' and also the next line:

$ sed '/Unix/{N;d;}' file
Cygwin
Solaris
AIX

     N command reads the next line in the pattern space. d deletes the entire pattern space which contains the current and the next line.

22. Delete only the next line containing the pattern 'Unix', not the very line:

$ sed '/Unix/{N;s/\n.*//;}' file
Cygwin
Unix
Solaris
AIX

     Using the substitution command s, we delete from the newline character till the end, which effective deletes the next line after the line containing the pattern Unix.

23. Delete the line containing the pattern 'Linux', also the line before the pattern:

$ sed -n '/Linux/{s/.*//;x;d;};x;p;${x;p;}' file | sed '/^$/d'
Cygwin
Solaris
AIX

    A little tricky ones. In order to delete the line prior to the pattern,we store every line in a buffer called as hold space. Whenever the pattern matches, we delete the content present in both, the pattern space which contains the current line, the hold space which contains the previous line.

   Let me explain this command: 'x;p;' ; This gets executed for every line. x exchanges the content of pattern space with hold space. p prints the pattern space. As a result, every time, the current line goes to hold space, and the previous line comes to pattern space and gets printed. When the pattern /Linux/ matches, we empty(s/.*//) the pattern space, and exchange(x) with the hold space(as a result of which the hold space becomes empty) and delete(d) the pattern space which contains the previous line. And hence, the current and the previous line gets deleted on encountering the pattern Linux. The ${x;p;} is to print the last line which will remain in the hold space if left.

  The second part of sed is to remove the empty lines created by the first sed command.

24. Delete only the line prior to the line containing the pattern  'Linux', not the very line:

$  sed -n '/Linux/{x;d;};1h;1!{x;p;};${x;p;}' file
Cygwin
Linux
Solaris
AIX

     This is almost same as the last one with few changes. On encountering the pattern /Linux/, we exchange(x) and delete(d). As a result of exchange, the current line remains in hold space, and the previous line which came into pattern space got deleted.

    1h;1!{x;p;} -  1h is to move the current line to hold space only if it first line. Exchange and print for all the other lines. This could easily have been simply: x;p . The drawback is it gives an empty line at the beginning because during the first exchange between the pattern space and hold space, a new line comes to pattern space since hold space is empty.

25. Delete the line containing the pattern 'Linux', the line before, the line after:

$ sed -n '/Linux/{N;s/.*//;x;d;};x;p;${x;p;}' file | sed '/^$/d'
Cygwin
AIX

     With the explanations of the last 2 commands, this should be fairly simple to understand.