sed examples to insert, append, and substitute text in your files

sed_examples.sh

sed -i \                             # -i: inplace; you can remove -i to do a dry run
  -e '/<pattern>/i <text>' \         # /i: insert text after the pattern
  -e '/<pattern>/a <text>' \         # /a: append text before the pattern
  -e 's/<pattern>/<text>/g'  \       # s/: substitute ; /g: global; match ALL instances instead of just the 1st match                 
  -e 's/(<pat1>)<random_text>(<pat2>)/\1 + \2'   # \1 reference <pat1>; \2 reference <pat2>
  input.file
  
# to loop through a directory 
find <directory>  -type f -exec sed -i -e 's/<pattern>/<text>/g' {} \;