Shell Programming and Scripting

awk -F'|' '{ s=s$1 }
           $1=="C"&&$2!=$3 {
             print "Balance error at line " NR
           }
           ($1=="A"&&NF!=4)||($1=="B"&&NF!=6)||($1=="C"&&NF!=3) {
             print "Wrong number of fields at line "NR
           }
           END {
             print s;gsub(/AB+C/,"",s)
             if(s=="")print "Syntax OK"
             else print "Syntax Error"
           } ' infile

syntax_error()
{
  echo syntax error in record $rec ending at line $line
  exit 1
}
while IFS="|" read label x; do
  line=$((line+1))
  check="$check$label"                                  # Append label to check variable
  case $label in
    A) rec=$((rec+1));;
    C) case $check in
         A*BC)
           check="${check%BC}"                          # Cut off trailing B and C
           check="${check#A}"                           # Then cut off leading A
           while [ "$check" != "${check%B}" ]; do       # Then cut off rest of trailing B's
             check="${check%B}"
           done
           [ "$check" = "" ] || syntax_error            # Something is wrong if check is not empty
           ;;
         *)    syntax_error                             # Something is wrong if pattern not A*BC
       esac ;;
  esac
done < infile
echo syntax is OK