RECAP OF MONDAY
- inner & outer joins
- self-joins: useful for answering questions like finding all pairs that
  meet some criteria
  -- A.observer < B.observer business is a standard idiom



## Next week:


=== BASH =================

GETTING HELP
- https://www.pcwdld.com/bash-cheat-sheet (and other cheat sheets)
- GNU manual
- shellcheck.net
- man, --help
- Google "... man page"

RUNNING COMMANDS
- I/O model for all programs running in Unix:
-- one input stream, stdin
-- two output streams, stdout & stderr
- Unix conventions:
-- programs read from stdin if no files specified on command line (ie, as args)
-- programs write to stdout
-- programs write error messages & out-of-band messages to stderr
- can pipe one program's stdout to another's stdin:
- wc -l *.csv | sort -n
- wc is given files, it reports #lines on those files
- wc -l 01_ASDN_Readme.txt
-- #lines for that file
- wc -l < 01_ASDN_Readme.txt
-- no files given, #lines in stdin
- equivalent: cat 01_ASDN_Readme.txt | wc -l
- on output side, try sqlite3 -csv database.db 'SELECT Code FROM Species'
-- cmd > output.dat
-- output o tfile, info message still appears because it's in stderr
-- > redirect stdout
-- 2> redirect stderr
-- >& stdout + stderr

PATH
- where are commands coming from?
- some are built in to Bash (cd, pwd, if, while)
- most are programs, whether from Unix (ls, mkdir, grep) or installed
  (sqlite3, python, etc.)
- Bash looks at PATH
- echo $PATH
- which -a command: see where a program is being read from
- PATH can be set in .bash_profile or .profile