Word Language

  [Quotes]        quotes        'abc'  $'\n'  "$var"
  [Substitutions] com-sub       $(command)   `command`   @(split command)
                  var-sub       ${var}   $0   $9   
                  arith-sub     $((1 + 2))
                  tilde-sub     ~/src
                  proc-sub      diff <(sort L.txt) <(sort R.txt)
  [Var Ops]       op-test       ${x:-default}  
                  op-strip      ${x%%suffix}  etc.
                  op-replace    ${x//y/z}
                  op-index      ${a[i+1}
                  op-slice      ${a[@]:0:1}
                  op-format     ${x@P}
