Package duct provides the internals for the duct command-line program wrapping code formatters that do not read from standard input data stream, and instead they take file names as command arguments. The package offers components that allow such commands to be wrapped inside of a standard Unix stdin to stdout filter-like data flow. The general idea is that input data read from standard input is written to an intermediate temporary file. The name of the file gets passed to as one of the positional arguments of the named program to be executed. The modified contents of the file are then re-read and written out the standard output. This way the wrapped program can be used as a regular Unix filter. Some code formatters take file names but do not modify files directly. Instead they write the formatted code to stdout or stderr. This scenario is supported by a the WrapWrite function that writes code from stdin to the temporary file but relies on the command's own stdout and/or stderr to write out the output.