====== Shell ======
eg. ''bash'' (''sh'' but "bourne" again), ''zsh'' (default for macOS), ''tcsh'' (NIH favorite)

===== Tutorials =====
  * https://www.tutorialspoint.com/unix/index.htm starts super super basic but covers advance topics (via Orma)
  * https://seankross.com/the-unix-workbench/command-line-basics.html
  * https://missing.csail.mit.edu/2020/shell-tools/ via Warren
  * https://www.learnshell.org/ (via Amar)
  * [[https://afni.nimh.nih.gov/pub/dist/doc/htmldoc/background_install/unix_tutorial/basic/basic_03.scripts.html|AFNI's unix intro]] to scripting
  * [[https://andysbrainbook.readthedocs.io/en/latest/unix/Unix_Intro.html|Andy's brain blog book unix chapter]] includes videos
  * Pitt's [[https://crc.pitt.edu/|center for research computing]] suggests 
    * https://cvw.cac.cornell.edu/Linux/default
    * https://software-carpentry.org/lessons/

==== Readline Keyboard Shortcut reference ====
 https://readline.kablamo.org/emacs.html

===== Utilities =====
fzf, fasd (z), readline editing options, alt+., ctrl+r, [[https://github.com/WillForan/fuzzy_arg|fuzzy ctrl+r, alt+n newfiles]]

===== Idioms  =====

short if-statements. short form function definitions. regexp w/BASH_REMATCH
<code=bash>
if [ -r file.txt ]; then
  rm file.txt
fi

# same as
[ -r file.txt ] && rm file.txt

# same as
test -r file.txt && rm "$_"

####

function abc {
  echo abc
}

# same as
abc(){ echo abc; }

###

foobar="a1 b2 c3"
[[ $foobar =~ c.* ]] && echo $BASH_REMATCH # c3
</code>

===== Input Arguments =====
Both functions and scripts take "input arguments": what's provided to the right of the script or function.


''"$#"'' is number input args, ''"$*"'' is all as single string ''"$@"'' is each argument quoted
''$1'' .. ''$9'' are input arguments 1 to 9 (('$0' is the scripts name, ''$FUNCNAME'' is the current function)). ''printf'' like ''echo'' but first argument is how to format what follows
<code=bash>
nargs()    { echo  "$#"; }
arg_at()   { nargs "$@"; }
arg_star() { nargs "$*"; }

arg_at   a b c # 3
arg_star a b c # 1

second()   { printf "*%s*\n" "$2"; }
arg_at2()  { second "$@"; }
arg_star2(){ second "$*"; }

arg_at2   a b c # *b*
arg_star2 a b c # **

</code>