the awesome power of recursive shell functions

Recursive shell functions allow you to build a pipeline dynamically. For example, if you want to print lines from standard input only if they match both of two regular expressions, you might do this:

grep2 () {
    grep -e "$1" | grep -e "$2"
}

But what if you want to allow any number of regular expressions? Here's the way:

mgrep () {
    if [ $# = 0 ]; then
        cat
    else
        pattern="$1"
        shift
        grep -e "$pattern" | mgrep "$@"
    fi
}