Notes on bash(1)

[Phil Pennock <phil@athenaeum.demon.co.uk>]

I recently needed to check something in bash(1) and noticed some
interesting points in the manual.  I'm throwing them this way for
discussion/whatever.  Bash is 2.01.1(1)-release.

* bash has arrays.  'declare', 'local' & 'readonly' each accept '-a' to
  declare an array.  Is it reasonable to add '-a' to 'typeset'?  This
  would automatically duplicate the bash-ism.
  Further, would it be an idea to then deprecate 'set -A' which
  overloads parameter setting onto 'set'?

* ${parameter/pattern/string} and ${parameter//pattern/string}
  pattern is expanded as per pathname expansion.  Longest match of
  pattern against parameter is replaced with string.  Once for / and for
  all instances with //.  #pattern anchors to beginning, %pattern
  anchors to end.  string may be null.  Applied to an array, this works
  on each element.
  zsh has a some of this with the colon-modifier 's'.
  The anchors in particular are nice.  They would make it easy to fully
  replicate basename(1) without forking.  We can't currently (AFAIK)
  accurately duplicate $(basename file .ext) (think - filename: .ext.ex)
  % base=${var:t:s/%.ext//}

* ${parameter:offset} and ${parameter:offset:length} provide substring
  and array extraction.  Both length and offset are arithmetic
  expressions.  length>=0.  offset may be negative to measure from end.
  zsh notably has ${parameter[start,stop]} already.  How desirable is
  this alternate syntax, given that zsh allows history modifiers in the
  same place?  It doesn't look like there would be a conflict, provided
  zsh requires $[...] for variables there.  Testing, bash allows:
  $ foo=abcde; t=2; echo ${foo:t}
-- 
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