Add pipeviewer (pv) and shell colors

[abkslm]

pv (Pipe Viewer) is a "terminal-based tool for monitoring the progress of data through a pipeline" (a-j-wood/pv/README.md). We propose creating a simpler analogue of pv to use as a progress bar for future programs within FogOS.

We also propose adding a switch for coloring of the FogOS shell, to enable a fun "rainbow" mode, where each output is generated as a sequence of ROY-G-BIV (for example, the first output would be red, second would be orange, etc). This is just for funsies (we propose psh or Pride Shell as a name for this mode).

Files added/modified:

• We will need to create a file user/pv.c, which will likely need to include types.h, stat.h, and user.h. No existing header files will need to be updated (most likely).
  • pv will be massively simplified compared to the widely-available version, in part because xv6 has very limited library support compared to Linux systems.
• We will need to modify user/sh.c to use a counter and an array of ANSI color codes to produce the rainbow output.

Team: Andrew B. Moore, Athene Marston

[malensek]

Sounds great!