The readtx statement reads a tape record, converts the tape record to hexadecimal, and assigns the resulting hexadecimal value to a specified variable.
readtx var[then|else|onerr statement.block]
The length of the tape record is specified by the most recently executed TCL t-att command.
The then clause is taken if the operation is successful.
Either else or onerr can be specified, but not both. If the tape unit has not been attached or if an end-of-file (eof) mark is read, the else or onerr clause, if present, is executed. In addition, the onerr clause can be used to check for end-of-tape (eot), tape unit not ready, parity error, or block transfer error.