sed is a command-line utility in Linux and Unix systems that is used for text processing. It is particularly useful for performing basic text transformations on an input file, such as substitution, deletion and addition of text.
The basic syntax for sed is:
sed 'command' inputfile
Where command is the command to be executed on the inputfile
Replace all occurrences of the word “pc” with “mac”:
sed 's/pc/mac/g' inputfile
Delete all lines that contain the word “mac”:
sed '/mac/d' inputfile
Insert the text “Hello, world!” at the beginning of each line:
sed 's/^/Hello, world! /' inputfile
Print only the lines from 2 to 5
sed -n '2,5p' inputfile
Substitute the word “pc” with “mac” only on the first line
sed '1 s/pc/mac/' inputfile
sed is a very powerful command that can be used to perform various text transformations. It can also use regular expressions for more advanced text processing.