Common sed Commands for Text Manipulation with Regular Expressions

This guide lists frequently used sed one‑liners for manipulating the contents of a file.

1. Print the first and third lines of 1.txt : sed -e '3p' -e '1p' -n 1.txt

2. Print from the first line to the last line (i.e., the whole file): sed -n '1,$'p 1.txt

3. Print lines 3 through 5: sed -n '3,5'p 1.txt

4. Delete all lines (from the first to the last): sed '1,$'d 1.txt

5. Delete the third and then the first line: sed -e '3d' -e '1d' 1.txt

6. Replace the letter r with R on the first line: sed '1s/r/R/g' 1.txt

7. Change lower‑case b to upper‑case B on lines 1‑2: sed '1,2s/b/B/g' 1.txt

8. General substitution syntax: s/pattern/replacement/g (global) or without g to replace only the first occurrence; any delimiter such as # can be used.

9. Replace every occurrence of nologin with NO : sed 's#nologin#NO#g' 1.txt

10. Delete all digits: sed 's/[0-9]//g' 1.txt 11. Delete all digits and colons: sed 's/[0-9]//g' -e 's/[:]//g' 1.txt 12. Add line numbers to each line (using grep -n and sed to strip the colon): grep -n '.*' 1.txt | sed 's/[:]//g' 13. Delete all lower‑case letters: sed 's/[a-z]//g' 1.txt Replace all lower‑case letters with A : sed 's/[a-z]/A/g' 1.txt 14. Remove every character that is not a lower‑case letter (i.e., keep only a‑z): sed 's/[^a-z]//g' 1.txt 15. Remove every character that is not a digit (i.e., keep only 0‑9): sed 's/[^0-9]//g' 1.txt 16. Convert all lower‑case letters to upper‑case: sed 's/[a-z]/\u&/g' 1.txt 17. Convert all upper‑case letters to lower‑case: sed 's/[A-Z]/\L&/g' 1.txt 18. Combine -n with substitution to print only the modified line, e.g., upper‑casing the first line: sed -n '1s/[a-z]/\u&/g'p 1.txt 19. Swap two fields separated by colons using extended regular expressions: sed -r 's/([^:]+)(:.*:)([^:]+$)/\3\2\1/' 1.txt Example swapping aa and ff in aa:bb:cc:dd:ee:ff yields ff:bb:cc:dd:ee:aa . 20. Perform the same swap with basic regular expressions (escaping parentheses): sed 's/\(aa\)\(.*\)\(ff\)/\3\2\1/' 1.txt 21. Use the -i option for in‑place editing (remember to back up the file first): sed -r -i 's/([^:]+)(:.*:)([^:]+$)/\3\2\1/' 1.txt