Input/Output

• echo builtin, options -e interprets backslash escaped characters, -n supresses trailing newline (prints on one line)
• read [option] [VARNAME1] builtin, reads user input, assigns to variables
• File descriptors are numbers that correspond to i/o streams: 0, 1, 2 are stdin, stdout, stderr respectively.
  • each process has /proc/<process_ID>/fd/<0-2> (not on mac?)
• M>N M is a file descriptor, N is a filename
• M>&N M is a fd, N is also a fd (M defaults to 1, stdout)

When executing a command, following steps in order are:
- if stdout of previous command is piped into stdin of current cmd, /proc/<current_process_ID>/fd/0 targets same anonymous pipe as /proc/<previous_process_ID>/fd/1
- if stdout of current cmd is piped to another, set ps output to another anonymous pipe