mdw@git.distorted.org.uk Git - tripe/blob - maint-utils/keysubst

   1 #! /bin/sh
   2
   3 ## This sed(1) script takes key/value pairs in tripe-admin(5) format as
   4 ## input; it writes sh(1) variable assignments as output.  The idea is that
   5 ## you can say
   6 ##
   7 ##      eval $(tripectl algs | sed "$keysubst")
   8 ##
   9 ## and have shell variables set from the output of the command.  The shell
  10 ## variable names are worked out from the key names, with sequences of
  11 ## nonalphanumerics replaced by single underscores.  Quoting is handled
  12 ## correctly, both on input and output.
  13 ##
  14 ## Theory of operation: firstly, ! and @ characters in the input are replaced
  15 ## by !e and !a respectively; this is a reversible transformation, which we
  16 ## undo at the end.  We now know that the input does not contain @.  We use a
  17 ## string of the form [lr][nqQ]@ as a cursor to move across the input from
  18 ## left to right.  The letters on the left of the @ are state markers: l
  19 ## means left of =, r means right; n means not in quotes; q means single-
  20 ## quoted; Q means double-quoted.
  21 ##
  22 ## This is a particularly awful hack.  I'm so sorry.
  23 keysubst='
  24         ## Initial transformation.
  25         s/!/!e/g'$p'
  26         s/@/!a/g'$p'
  27
  28         ## Initial state: left-hand side, not quoted
  29         s/^/ln@/'$p'
  30
  31 :loop
  32         ## Reached the end: exit.
  33         /@$/ b end
  34
  35         ## Enter or leave quoted state as necessary.
  36         s/\(.\)n@'\''/\1q@/'$p'
  37         s/\(.\)n@"/\1Q@/'$p'
  38         s/\(.\)q@'\''/\1n@/'$p'
  39         s/\(.\)Q@"/\1n@/'$p'
  40         t loop
  41
  42         ## Leave backslashed things alone.
  43         /\(..\)@\\/ {
  44           s//\1@/
  45           b lit
  46         }
  47
  48         ## Unquotes spaces delimit key/value pairs.
  49         s/\(rn\)@[      ]\+/'\'' ln@/'$p'
  50
  51         ## An = sign separates left and right sides.
  52         s/l\(.\)@=/='\''r\1@/'$p'
  53
  54         ## Single quotes on the right-hand side need special care.
  55         t loop
  56         s/r\(.\)@'\'/\''\\'\'\''r\1@/'$p'
  57
  58         ## Sequences of alphanumerics are always easy.
  59         s/\(..\)@\([[:alnum:]]\+\)/\2\1@/'$p'
  60
  61 :lit
  62         ## Convert bad left-hand-side characters to underscores.
  63         t loop
  64         s/l\(.\)@\(!.\|[^=![:alnum:]]\)\+/_l\1@/'$p'
  65
  66         ## Convert sequences of nonproblematic right-hand-side characters.
  67         t loop
  68         s/\(r.\)@\([^   '\''"`]\+\)/\2\1@/'$p'
  69
  70         ## And anything else is probably OK.
  71         s/\(..\)@\(.\)/\2\1@/'$p'
  72         b loop
  73
  74 :end
  75         ## Unquote the end appropriately.
  76         s/r.@/'\''/'$p'
  77         s/..@//'$p'
  78
  79         ## And undo the initial transformation.
  80         s/!a/@/g'$p'
  81         s/!e/!/g'$p'
  82 '
  83
  84 sed "$keysubst"