IsNotEmptyAndExists checks the given file exists and is not empty.

Pwd returns the process working directory.

ReadInput reads bytes from inputPath (if not empty) or stdin.

ToAbsPath turns a relative path into an absolute path with the given root path, absolute paths are ignored.

WriteOutput writes given bytes into outputPath (if not empty) or stdout.

ErrExpectedStdin indicates that an stdin pipe was expected but not present.