inserting text into a specific line

Question

I\'ve got a text file, and using Bash I wish to insert text into into a specific line.

Text to be inserted for example is !comment: http://www.test.com into

Answer 1

Using man 1 ed (which reads entire file into memory and performs in-place file editing without previous backup):

# cf. http://wiki.bash-hackers.org/doku.php?id=howto:edit-ed
line='!comment: http://www.test.com'
#printf '%s\n' H '/!eeee/i' "$line" . wq | ed -s file
printf '%s\n' H 5i "$line" . wq | ed -s file