Reads input from files (or the standard input, if none are supplied) and prints it on the standard input, expanding references to environment variables with their actual values.

All POSIX-compatible shell constructs are understood: $NAME, ${NAME}, ${NAME:-word}, ${NAME+=word}, ${NAME:=word}, ${NAME:?word}.

A special ternary construct is provided: ${NAME:|word1|word2}, which substitutes the expansion of word1 if NAME is set and the expansion of word2 otherwise.

Additionally, conditional statements, comments and quote sequences are provided as well.