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sed Command in Linux with Examples (Beginner to Advanced)

The sed (Stream Editor) command in Linux is used for text manipulation. It processes and edits text files in a non-interactive way, making it useful for automation.

1. Basic Syntax

sed [options] 'command' file
  • [options] → Additional options (like -i for in-place editing).
  • 'command' → The operation to perform.
  • file → The target file.

2. Print File Content (Default Behavior)

sed '' file.txt

If no command is given, sed prints the file as is.

3. Substituting (Replacing) Text

sed 's/old/new/' file.txt
  • Replaces the first occurrence of “old” with “new” in each line.
sed 's/old/new/g' file.txt
  • Replaces all occurrences of “old” with “new” in each line (g = global replacement).
sed -i 's/old/new/g' file.txt
  • Edits the file in place instead of just displaying output.

4. Replace Text on a Specific Line

sed '3s/old/new/' file.txt
  • Replaces “old” with “new” only on line 3.

5. Delete Lines

sed 'd' file.txt
  • Deletes all lines (prints nothing).
sed '3d' file.txt
  • Deletes line 3.
sed '2,5d' file.txt
  • Deletes lines 2 to 5.
sed '/pattern/d' file.txt
  • Deletes lines containing “pattern”.

6. Print Specific Lines

sed -n '3p' file.txt
  • Prints only line 3.
sed -n '2,5p' file.txt
  • Prints lines 2 to 5.
sed -n '/pattern/p' file.txt
  • Prints lines containing “pattern”.

7. Add Text Before or After a Line

sed '3i This is inserted before line 3' file.txt
  • Inserts text before line 3.
sed '3a This is inserted after line 3' file.txt
  • Inserts text after line 3.

8. Replace Only Whole Words

sed 's/\<word\>/replacement/g' file.txt
  • Ensures only whole occurrences of “word” are replaced.

9. Find and Replace Using Regular Expressions

sed 's/[0-9]/#/g' file.txt
  • Replaces all numbers with #.
sed 's/[A-Za-z]/*/g' file.txt
  • Replaces all letters with *.

10. Change Case (Uppercase/Lowercase)

sed 's/[a-z]/\U&/g' file.txt
  • Converts lowercase letters to uppercase.
sed 's/[A-Z]/\L&/g' file.txt
  • Converts uppercase letters to lowercase.

11. Multiple Substitutions

sed -e 's/foo/bar/g' -e 's/hello/world/g' file.txt
  • Replaces “foo” with “bar” and “hello” with “world”.

12. Remove Empty Lines

sed '/^$/d' file.txt
  • Deletes empty lines.

13. Remove Leading and Trailing Spaces

sed 's/^[ \t]*//;s/[ \t]*$//' file.txt
  • Removes spaces from the beginning and end of each line.

14. Replace the Nth Occurrence of a Word

sed 's/foo/bar/2' file.txt
  • Replaces only the second occurrence of “foo” on each line.

15. Swap Words in a Line

sed 's/\(word1\) \(word2\)/\2 \1/' file.txt
  • Swaps “word1” and “word2” in each line.

16. Extract Specific Columns (Like cut)

sed 's/[^ ]* //' file.txt
  • Removes the first word in each line.

17. Replace Text Between Two Patterns

sed '/start/,/end/s/foo/bar/g' file.txt
  • Replaces “foo” with “bar” only between “start” and “end” lines.

18. Append a String to Every Line

sed 's/$/ - Appended text/' file.txt
  • Appends ” – Appended text” at the end of each line.

19. Insert Line Numbers

sed = file.txt | sed 'N;s/\n/\t/'
  • Adds line numbers before each line.

20. Backup Original File Before Editing

sed -i.bak 's/old/new/g' file.txt
  • Creates a backup file.txt.bak before modifying file.txt.

The sed command is a powerful tool for text manipulation, from simple replacements to advanced pattern matching.