sed

print specific line number from file

sed 'n!d' file

add character

s/regex/&n/

convert first word before equals symbol from lower to upper this is used in config files such as ifcfg to convert all variable names

:%s/^[[:alpha:]_]\{1,\}=/\U&/

append line after match

sed '/match/a hello friend' filename

prepend line before match

sed '/match/i hello friend' filename

{upper,lower}case test

sed 's/[a-z].*=/\U&/' filename

this example is for uppercasing var names in a rhel network config file http://bigdatums.net/2017/09/30/how-to-uppercase-lowercase-text-with-sed/