### 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