sed

• Replace foo with bar in a file :)

Bash

 sed -i 's/foo/bar/g' /some/path/file.txt

Replace "dark" or "somecrap" or "light" to "boles"

Bash

 sed -i 's/dark/boles/g;s/somecrap/boles/g;s/light/boles/g' /some/path/file.txt

• Delete line using matching patterns in a line

Bash

sed -i '/pattern-to-match/d' ./some/file

• Mach based on part of a pattern

Bash

sed -i '/backend=/c\  export backend=soemthing' somefile