# get text in one file
grep version package.json

# get text in all file
grep version ./*

# get text in all folder
grep -r "function" ./*js

# get text in regex folder
grep -r --include="*.js" "function" .
# same way
find . -name "*.js" | xargs grep "function"

# get match file line number
grep -n version package.json

# get match file line number and with after 2 other line -A after -B before -C both
grep -nA 2 version package.json

# not need escaped special
grep --color -E "###+" readme.md