bin/bre-invert-word


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#! /bin/sh
# bre-invert-word : string -> BRE
set -euf

# TODO escape chars in the resulting BRE.
awk -v input="$1" '
  BEGIN {
    split(input,s,"")
    for (i in s) {
      c=s[i]
      printf "\\|%s[^%s]", y, c
      y = y c
    }
  }
'