\section psub psub - perform process substitution

\subsection psub-synopsis Synopsis
\fish{synopsis}
COMMAND1 (COMMAND2|psub [-f])
\endfish

\subsection psub-description Description

Posix shells feature a syntax that is a mix between command
substitution and piping, called process substitution. It is used to
send the output of a command into the calling command, much like
command substitution, but with the difference that the output is not
sent through commandline arguments but through a named pipe, with the
filename of the named pipe sent as an argument to the calling
program. `psub` combined with a
regular command substitution provides the same functionality.

If the `-f` or `--file` switch is given to `psub`, `psub` will use a
regular file instead of a named pipe to communicate with the calling
process. This will cause `psub` to be significantly slower when large
amounts of data are involved, but has the advantage that the reading
process can seek in the stream.

\subsection psub-example Example

`diff (sort a.txt|psub) (sort b.txt|psub)` shows the difference
between the sorted versions of files a.txt and b.txt.