Linux Sed commnad (Replacing and Filtering )

The Linux operating system makes use of terminal commands to work with a computer's file system. The primary use of the Linux command sed, which is short for stream editor, is to modify each line of a file or stream by replacing specified parts of the line. It makes basic text changes to a file or input from a pipeline. 

For example, say you have a file named "songs.text" that contains these lines:

1, Justin Timberlake, Title 545, Price $6.30

2, Taylor Swift, Title 723, Price $7.90

3, Mick Jagger, Title 610, Price $7.90

4, Lady Gaga, Title 118, Price $6.30

5, Johnny Cash, Title 482, Price $6.50

6, Elvis Presley, Title 335, Price $6.30

7, John Lennon, Title 271, Price $7.90

Making Text Substitutions With Sed

If you want to change all price occurrences of $6.30 to $7.30, you can make the changes using the sed command in this way:

sed 's/6.30/7.30/' songs.txt > songs2.txt

This code makes the change and writes the modified file to "songs2.txt". The output file contains:

1, Justin Timberlake, Title 545, Price $7.30

2, Taylor Swift, Title 723, Price $7.90

3, Mick Jagger, Title 610, Price $7.90

4, Lady Gaga, Title 118, Price $7.30

5, Johnny Cash, Title 482, Price $6.50

6, Elvis Presley, Title 335, Price $7.30

7, John Lennon, Title 271, Price $7.90

If you want to replace all occurrences of "Cash" with "Trash" you use:

sed 's/Cash/Trash/' songs.txt > songs2.txt

which creates a file with content:

1, Justin Timberlake, Title 545, Price $7:30

2, Taylor Swift, Title 723, Price $7.90

3, Mick Jagger, Title 610, Price $7.90

4, Lady Gaga, Title 118, Price $7:30

5, Johnny Trash, Title 482, Price $6.50

6, Elvis Presley, Title 335, Price $7:30

7, John Lennon, Title 271, Price $7.90

Filtering With the Sed Command

Sed is also frequently used to filter lines in a file or stream. For example, if you only want to see the lines containing "John," you use:

sed -n '/John/p' songs.txt > johns.txt

which writes the following lines to file johns.txt:

5, Johnny Trash, Title 482, Price $6.50

7, John Lennon, Title 271, Price $7.90

https://www.lifewire.com/example-uses-of-sed-