JSON Uglify (Bash)

json-uglify.sh

#!/bin/bash

SELF="$( basename "$0" )"

# new-line char is skipped here
while read -r LINE; do
  while [ -n "$LINE" ]; do
    # skip whitespaces
    [[ "$LINE" =~ ^[$' \t\r\n']+ ]] && {
      PART="${BASH_REMATCH[0]}"
      LINE="${LINE:${#PART}}"
    }

    CHAR="${LINE:0:1}"
    PART=''
    case "$CHAR" in
      [\][{},:])
        PART="$CHAR"
        ;;

      \")
        [[ "$LINE" =~ ^\"([^\"\\]|\\.)*\" ]] || {
          echo "$SELF: cannot match \"string\"" >&2
          exit 2
        }
        PART="${BASH_REMATCH[0]}"
        ;;

      [-0-9])
        [[ "$LINE" =~ ^-?(0|[1-9][0-9]*)(\.[0-9]+)?([eE][-+]?[0-9]+)? ]] || {
          echo "$SELF: cannot match number" >&2
          exit 2
        }
        PART="${BASH_REMATCH[0]}"
        ;;

      # null | true, assuming the input IS already correct JSON
      n|t)
        PART="${LINE:0:4}"
        ;;

      # false, assuming the input IS already correct JSON
      f)
        PART="${LINE:0:5}"
        ;;

      ?)
        echo "$SELF: unexpected char $CHAR" >&2
        exit 2
    esac
    echo -n "$PART"
    LINE="${LINE:${#PART}}"
  done
done
# new-line in the end
#echo ''