sed is most often used for replacing text in a file

$ sed s/cat/dog/g file.txt
“cat"can be a regular expression

change a file in place. with -i

person: in GNU sed it’s -i, in BSD sed, -i SUFFIX confuses me every time.

Some more sed incantations…

sed -n 12 p

print 12th line -n suppresses output so only what you print with ‘p’ gets printed

sed 5 d

delete 5th line

sed /cat/d

delete lines matching /cat/

sed -n 5,30 p

print lines 5-30

sed s+cat/+dog/+

(’+’ can be any character)
Use + as a regex delimeter
person: way easier than escaping /s like s/cat//dog//!

sed -n s/cat/dog/p

only print changed lines.

sed G

double space a file (good for long error lines)

sed /cat la dog’

append ‘dog’ after lines containing ‘cat’

sed ‘i 17 panda”

insert “panda” on line 17