You are very kind! It's dangerous to encourage me!



Knowing "how simple it really is" is simpler than learning tons by rote. Using truss/tusc/strace can be very educational, showing you all the calls under the covers. To round it out (never ends), this needs:Mostly a basic ksh list, ksh93 and bash goes on much farther. Begs the need for the arithmetic bits, date/time bits, test, with regex matching, case. I love 'case', because it structures testing so all cases are addressed, and facilitates nice commenting! Just use balanced () in case patterns, so the vi % feature is not incapacitated.

BTW, a nice use of 'line' and subshell is to avoid using a command that must pass all the data, just to remove the header line(s) before processing:

Code:

( . . . | ( line >&2 ; sort ) >output_file ) 2>>log_file

Subshell is also great for collecting logging or multipel commands' output without saying >>file_name over and over, like the stderr to log_file above. Trailer lines are a different problem, maybe time to learn some sed:

Code:

 . . . | sed '
  ${
    w trailer_file
    d
   }
 ' | . . . .

The best training is for use, not to pass a certification by knowing every dumb feature; to know which pragmas are useful, clear, fast and robust. It does not hurt to teach formatting in a normal way, so it reads well for review and maintenance. In all code, a common sin is not formatting lists of predicates or actions on separate lines, not throwing in blank lines and indentation so multi-line formatted commands and container expressions like if stand out from surrounding single-line commands. Both the quality of your work and the size and speed of project you can execute are enhanced by good formatting, good logging and good error handling. Don't learn to be a weak, hope and prayer, cryptic script writer; it is not worth the pain or the limitation. You, too, deserve well behaved, robust, easily read, tracable code, even in shells!

PPS: if you only use cd inside subshells, you never leave ~ $HOME, and all your commands can be recalled and rerun using $EDITOR=vi and ksh set -o vi and the like. Increase you $HISTSIZE to 32767, put your $HISTFILE on permanent, and if possible net mounted, disk (not /tmp), periodically save your $HISTFILE, and recall how you did it the last time using escape /pattern. This is the nicest Character User Interface (CUI) this side of becoming an emacs addict. It saves you more typing than cd of your login shell ever did, and reduces mistakes - running a command in the wrong directory. The path you used to type in to cd can be recalled and reused with the whole command 'line' (can be many line single shell command). Recalled commands are also good starters for scripts. Really long command lines need to be passed through vi (escape /pattern v) to avoid being truncated, but still work over and over!