What is /bin/red
Solution 1:
red is ed in restricted mode.
$ whatis red
red (1) - line-oriented text editor
$ man red
shows `ed` man page.
Also, the code shows, it executes ed --restricted from bindir with all arguments ("$@").
For a manual on ed and its commands, run info Ed.
In the chapter Invoking ed:
The format for running 'ed' is:
ed [OPTIONS] [FILE] red [OPTIONS] [FILE][...]
'-r' '--restricted' Run in restricted mode. This mode disables edition of files out of the current directory and execution of shell commands.