online and in the aptly named book sed & awk by Dale Dougherty and Arnold
Robbins.
sed and awk aren’t used much anymore, at least not by people who have
entered the profession in the twenty-first century, but they are beloved by
those who take the time to learn them. For this edition of the book, we are
including only a brief mention and a couple quick examples—certainly not
enough to really learn to use either in a large capacity. If there is significant
interest, we may break this out and expand it into a separate chapter in a
future edition.
You use sed with sed commands, like this:
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matthew@seymour:~$ sed sedcommand inputfile
matthew@seymour:~$ sed -e sedcommand inputfile
matthew@seymour:~$ sed -e sedcommand -e anothersedcommand inputfile
The second example does the same thing as the first example, except that it
specifically denotes the command to run. This is optional when there is only
one command, but it is useful when you want to run other commands, as in
the third example.
Let’s say you want to change every instance of camel in the text file
transportation.txt to dune buggy. Here is how you do that:
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matthew@seymour:~$ sed -e 's/camel/dune buggy/g' transportation.txt
The s command stands for substitution. It is surrounded by ‘ marks to
prevent confusion with spaces or other characters in the strings it contains.
The s is followed by / (slash), which is a delimiter separating the parts of the
command from one another. Next is the pattern to match, followed by what it
will be changed to. Finally, the letter g means to replace it globally, or
everywhere in the text file that camel occurs.
You can process text based on line numbers in the file. If you wanted to delete
lines 4 through 17 in the file longtext.txt, you would do this:
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matthew@seymour:~$ sed -e '4,17d' longtext.txt
The characters used for sed commands are generally obvious, like the d in
this example standing for delete. You can use a regular expression in place of
the line numbers. You can also use other commands besides substitute and
delete. You can use sed in scripts and chain commands together.