How do I find a word in a file and insert text two lines below that?

Question

I have a file that I want to find a key word in and enter text 2 lines down.

For example lets say the file i have contains the following words

the
cow
goes
moo

I want to be able to find the word "cow" and enter the text "yay" into the file 2 lines below the word cow.

the
cow
goes
moo
yay

I believe this would be done with sed but cannot get it to work.

Any help is greatly appreciated.

Answer 1

$ cat ip.txt 
the
cow
goes
moo

$ sed '/cow/{N;N; s/$/\nyay/}' ip.txt 
the
cow
goes
moo
yay

• N;N; get next two lines
• s/$/\nyay/ add another line

Answer 2

With awk:

awk '/cow/ {print; getline; print; getline; print; print "yay"; next}; 1'

• /cow/ matches cow in the record, and then {print; getline; print; getline; print; print "yay"; next} prints the line, getline gets us the next line, that is printed too, same for the next, and then yay is printed, then goes to the next line (next)

• 1 (true) will print the rest of the lines as default action

Caveat:

• If there are less that two lines between the pattern to search and EOF, then the last line starting from pattern will be repeated to make two lines in between

Example:

% cat file.txt
the
cow
goes
moo

% awk '/cow/ {print; getline; print; getline; print; print "yay"; next}; 1' file.txt
the
cow
goes
moo
yay

Answer 3

Other sed

sed '/cow/! b;n;n;a\yay' file.txt

Other awk

awk '{print;this--};/cow/{this=2}! this{print "yay"}' file.txt

Answer 4

With ed

ed file << EOF
/cow/+2a
yay
.
,p
q
EOF

to print the modified output; or

ed file << EOF
/cow/+2a
yay
.
wq
EOF

or (as a bash one-liner)

printf '%b\n' '/cow/+2a' 'yay\n.' 'wq' | ed file

to write the changes in place.