Sed technique

Replace only those that match the context pattern, such as ： If c It is not the letter that follows A, will c Switch to b

echo "c.cAcf" | sed 's/c/([^A]/)/b/1/g'
Output b.cAbf

 

Precede the line that matches the rule , Insert a specific character

 

echo "abcef" | sed '/ab/ s/^/#/'

 

among /ab/ It's a regular expression , Used to match a line ,

s/^/#/ Command is replace , ^ At the beginning of the line