Top 20 Commands with explanation of “sed” command

The sed (Stream Editor) command is a powerful Linux tool used for text processing. It allows for text substitution, deletion, insertion, and more, directly from the command line. This command is widely used in shell scripting, automation, and data manipulation tasks.

Here is a detailed, humanized, and well-explained list of the top 20 sed commands:

---

1. Basic String Substitution

Replace the first occurrence of “old” with “new” in a line

echo "I love old books" | sed 's/old/new/'

Output:

I love new books

✔ How it works:

• s/old/new/ → s stands for substitute. It replaces the first occurrence of “old” with “new”.

---

2. Replace All Occurrences in a Line

To replace every occurrence of “old” with “new”, use the g (global) flag

echo "old books are old but valuable" | sed 's/old/new/g'

Output:

new books are new but valuable

✔ How it works:

• g → This flag tells sed to replace all occurrences in a line instead of just the first one.

---

3. Replace Text in a File

Modify a file directly

sed 's/Linux/Unix/g' file.txt

✔ How it works:

• This replaces “Linux” with “Unix” in every line of file.txt, but does not modify the actual file.

💡 To save changes to the file:

sed -i 's/Linux/Unix/g' file.txt

✔ -i modifies the file in place.

---

4. Replace a Specific Line

Replace text only in line 3

sed '3s/Linux/Unix/' file.txt

✔ How it works:

• 3s/Linux/Unix/ → Only the third line is modified.

---

5. Replace Text Between Line Ranges

Change “hello” to “hi” only from lines 2 to 5

sed '2,5s/hello/hi/g' file.txt

✔ How it works:

• 2,5s/hello/hi/g → Substitutes “hello” with “hi” only between lines 2 to 5.

---

6. Delete a Specific Line

Remove line number 3

sed '3d' file.txt

✔ How it works:

• 3d → Deletes line 3 from file.txt.

---

7. Delete a Range of Lines

Remove lines 2 to 5

sed '2,5d' file.txt

✔ How it works:

• 2,5d → Deletes lines from 2 to 5.

---

8. Delete Empty Lines

Remove all blank lines

sed '/^$/d' file.txt

✔ How it works:

• /^$/d → Deletes lines where there is nothing (^$ represents an empty line).

---

9. Insert a Line Before a Specific Line

Add a line before line 3

sed '3i This is an inserted line' file.txt

✔ How it works:

• 3i → Inserts the text before line 3.

---

10. Insert a Line After a Specific Line

Add a line after line 3

sed '3a This is an added line' file.txt

✔ How it works:

• 3a → Appends the text after line 3.

---

11. Replace a Word Only If It Matches a Pattern

Replace “red” with “blue” only in lines containing “apple”

sed '/apple/s/red/blue/' file.txt

✔ How it works:

• /apple/ → Only matches lines containing “apple”.
• s/red/blue/ → Replaces “red” with “blue”.

---

12. Print Only Modified Lines

Show only lines where “error” is replaced with “warning”

sed -n 's/error/warning/p' file.txt

✔ How it works:

• -n → Suppresses normal output.
• p → Prints only modified lines.

---

13. Print Specific Lines from a File

Display only lines 2 to 4

sed -n '2,4p' file.txt

✔ How it works:

• -n → Suppresses normal output.
• 2,4p → Prints lines 2 to 4.

---

14. Replace Multiple Words

Change both “Linux” to “Unix” and “cloud” to “server”

sed -e 's/Linux/Unix/g' -e 's/cloud/server/g' file.txt

✔ How it works:

• -e allows multiple substitutions.

---

15. Remove Trailing Whitespaces

sed 's/[[:space:]]*$//' file.txt

✔ How it works:

• [[:space:]]*$ → Removes spaces at the end of each line.

---

16. Replace Text Between Delimiters

Change text inside [ ]

echo "[hello]" | sed 's/\[.*\]/[hi]/'

✔ How it works:

• \[.*\] → Matches everything inside [].
• Replaces it with [hi].

---

17. Use a Different Delimiter

Avoid conflicts with / by using #

sed 's#/home/user#/var/www#g' file.txt

✔ How it works:

• # is used as a separator instead of / to avoid conflicts.

---

18. Save Output to a New File

sed 's/Linux/Unix/g' file.txt > newfile.txt

✔ How it works:

• Redirects the modified content to newfile.txt without changing file.txt.

---

19. Modify Only the First 5 Lines

sed '1,5s/old/new/g' file.txt

✔ How it works:

• 1,5s/old/new/g → Changes only in the first 5 lines.

---

20. Use sed with a Shell Script

Create a script (modify_text.sh):

#!/bin/bash
sed -i 's/Linux/Unix/g' file.txt

✔ How it works:

• -i edits file.txt directly.
• You can now run ./modify_text.sh to apply the changes.

---

Final Thoughts

• sed is like a Swiss army knife for text processing.
• You can replace, delete, modify, insert, and format text efficiently.
• Combining sed with grep, awk, and regex makes it even more powerful.