gistfile1.sh

# SINGLE-QUOTED
# text between the single-quotes is read as a plain string
$ echo 'foo "bar" `baz`'
foo "bar" `baz`

# BACK-QUOTED
# text between the back-quotes is read as a command
$ echo `echo "foo"`
foo

# DOUBLE-QUOTED
# any nested back-quotes are to be read as commands
# all other text between the double-quotes is read as a plain string
$ echo "hello `echo "world"`"
hello world

gistfile2.txt

cat * | grep foo

=>

Pipe(Call(Cat(), ["a.txt", "b.txt"]), Call(Grep(), ["foo"]))