Basic Linux command (sed)

sed command is stream editor for filtering and transforming text.

cheulong@master-node:~$ cat hawaii-pizza.txt
Ingredients:
1. Flour
2. Mozzarella
3. Cheese
4. Ham
5. Pizza sauce
6. Pineapple Pineapple

Let replace pineapple from the list

# file doesn't change, only output
sed 's/Pineapple/Feta/' hawaii-pizza.txt

---
Ingredients:
1. Flour
2. Mozzarella
3. Cheese
4. Ham
5. Pizza sauce
6. Feta Pineapple

By default, the sed command replaces the first occurrence of the pattern in each line

Replace

To replacing the nth occurrence of a pattern in a Line

sed 's/Pineapple/Feta/2' hawaii-pizza.txt

# All occurrence 
sed 's/Pineapple/Feta/g' hawaii-pizza.txt
# second occurrence to all occurrence 
sed 's/Pineapple/Feta/2g' hawaii-pizza.txt

Change in-place

# replace string
sed -i 's/Pineapple/Feta/' hawaii-pizza.txt

Replacing String on a Specific Line Number

sed '3 s/./!/' hawaii-pizza.txt

Printing Only the Replaced Lines

sed -n 's/Pineapple/Feta/' hawaii-pizza.txt

Replacing String on a Range of Lines

sed '1,3 s/./!/' hawaii-pizza.txt
# from line 2 to last
sed '2,$ s/./!/' hawaii-pizza.txt

Delete

Remove something

sed 's/Feta//' hawaii-pizza.txt
---
Ingredients:
1. Flour
2. Mozzarella
3. Cheese
4. Ham
5. Pizza sauce
6. 

Delete Line

sed '2d' hawaii-pizza.txt

Delete Last Line

sed '$d' hawaii-pizza.txt

To Delete line from range x to y

sed '4,$d' hawaii-pizza.txt

Insert

Insert Text

sed '3i\Break' hawaii-pizza.txt  # Insert text before line 3
sed '3a\Break' hawaii-pizza.txt  # Insert text after line 3

Best Practices

• Be sure to back up your files before applying for the changes. (especially while using -i)
• Be careful before using regular expressions to avoid any unintended change.
• Always test your SED command on sample file first before using it to avoid unintentional change.

Leave a comment if you have any questions.

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