Substituting a single line with multiple lines of text - linux

Question

In Linux what command can I use to replace a single line of text with new multiple lines? I want to look for a keyword on a line and delete this line and replace it with multiple new lines. So in the text shown below I want to search for the line that contains "keyword" and replace the entire line with 3 new lines of text as shown.
For example replacing the line containing the keyword,
This is Line 1
This is Line 2 that has keyword
This is Line 3
changed to this:
This is Line 1
Inserted is new first line
Inserted is new second line
Inserted is new third line
This is Line 3

Answer 1

$ sed '/keyword/c\
> Inserted is new first line\
> Inserted is new second line\
> Inserted is new third line' input.txt
This is Line 1
Inserted is new first line
Inserted is new second line
Inserted is new third line
This is Line 3
$ and > are bash prompt

Answer 2

Create a file, script.sed, containing:
/keyword/{i\
Inserted is new first line\
Inserted is new second line\
Inserted is new third line
d
}
Apply it to your data:
sed -f script.sed your_data
There are numerous variations on how to do it, using the c and a commands instead of i and/or d, but this is reasonably clean. It finds the keyword, inserts three lines of data, and then deletes the line containing the keyword. (The c command does that all, but I didn't remember that it existed, and the a command appends the text and is essentially synonymous with i in this context.)

Answer 3

you can do it using shell builtins too:
STRING1_WITH_MULTIPLE_LINES="your
text
here"
STRING2_WITH_MULTIPLE_LINES="more
text"
OUTPUT=""
while read LINE || [ "$LINE" ]; do
case "$LINE" in
"Entire line matches this")OUTPUT="$OUTPUT$STRING1_WITH_MULTIPLE_LINES
";;
*"line matches this with extra before and/or after"*)OUTPUT="$OUTPUT$STRING2_WITH_MULTIPLE_LINES
";;
*)OUTPUT="$OUTPUT$LINE
";;
esac
done < file
echo "$OUTPUT" >file