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Cheulong Sear
Cheulong Sear

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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
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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
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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
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Change in-place

# replace string sed -i 's/Pineapple/Feta/' hawaii-pizza.txt
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Replacing String on a Specific Line Number

sed '3 s/./!/' hawaii-pizza.txt
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Printing Only the Replaced Lines

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

Remove something

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

sed '2d' hawaii-pizza.txt
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Delete Last Line

sed '$d' hawaii-pizza.txt
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To Delete line from range x to y

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