sed Scripting

sed Options

As with many command-line tools, sed has options available when you enter the command.

e
necessary ONLY if you enter more than 1 instruction on the command line
n
suppress the default action of outputting every line
f
a script filename follows

e

Yes, you can have more than 1 instruction with sed. This is just one way to do that.

sed -e 's/noon/3pm/' -e 's/fox/giraffe/' sedit.txt
The quick brown giraffe slept until 3pm

Another way is to separate each instruction with a semi-colon:

sed 's/noon/3pm/;s/fox/giraffe/' sedit.txt
The quick brown giraffe slept until 3pm

Or, for better clarity, you can put each instruction on a separate line:

sed '
s/noon/3pm/
s/fox/giraffe/
s/quick/slow/
' sedit.txt
The slow brown giraffe slept until 3pm

n

A note about n: as noted, the default action is to print every line. Using n, if you want to print a line, you must include a print command p following the last slash:

sed -n 's/noon/3pm/' sedit.txt

produces no output, while

sed -n 's/noon/3pm/p' sedit.txt
The quick brown fox slept until 3pm

does.

f

If you've progressed to the point of writing sed scripts, this is how to indicate that:

sed -f mySedScript.txt sedit.txt
The slow brown giraffe slept until 3pm

The script file mySedScript.txt contains

s/noon/3pm/
s/fox/giraffe/
s/quick/slow/

Before writing scripts, try to follow these points

Think through want you want to do before you do it

Explicitly describe a procedure to do it

Test, test, test before committing to the final script

Recall that

Have no fear.
The cool thing about sed is that it DOES NOT alter the file, only the OUTPUT.

so to save the changes to a file, you have to redirect to a new file.

sed -f mySedScript.txt sedit.txt > NewSedit.txt