UNIX for Dummies Questions & Answers

#!/bin/ksh
recno=0         # Record number
recid=""        # Record ID 1/2/3/4
prev_recid="0"  # Previous record ID
#
cat filename.txt | while read line
do
        recno=$(( $recno + 1 ))
        recid=$(echo "${line}"|cut -c1-1)
        case "${recid}" in
                "1")
                        prev_recid="${recid}"
                        continue
                        ;;
                "2")
                        if [ "${prev_recid}" = "1" ]
                        then
                                prev_recid="${recid}"
                                continue
                        fi
                        if [ "${prev_recid}" = "3" ]
                        then
                                prev_recid="${recid}"
                                continue
                        fi
                        # Error. Do not use for subsequent compares
                        echo "Out of sequence : record ${recno}"
                        echo "${line}"
                        continue
                        ;;
                "3")
                        if [ "${prev_recid}" = "2" ]
                        then
                                prev_recid="${recid}"
                                continue
                        fi
                        # Error. Do not use for subsequent compares
                        echo "Out of sequence : record ${recno}"
                        echo "${line}"
                        continue
                        ;;
                "4")
                        prev_recid="${recid}"
                        continue
                        ;;
                *)
                        # Error. Do not use for subsequent compares
                        echo "Unknown record type : record ${recno}"
                        echo "${line}"
                        continue
                        ;;
        esac
done

./script.sh
Out of sequence : record 12
3PLAYER25 000011000003000