\section{Conditional Execution Commands} \label{Conditional Execution Commands} All conditonal execution commands are of the form: \medskip \centerline{\tt n"X command-string '} \centerline{or} \centerline{\tt n"X then-command-string | else-command-string '} \medskip In the first form of the command, {\tt n} is a numeric argument on which the decision is based, {\tt X} is any of the conditional execution commands listed in table~\ref{Conditional Execution Commands}, and {\tt command string} is the command string which will be executed if the condition is satisfied. The numeric argument is separated from the conditional execution command by a double quote ({\tt "}) and the command string is terminated with an apostrophe {\tt '}. If the condition is not satisfied, the command string will not be executed; execution will continue with the first command after the apostrophe. In the second form of the command, two command strings are specified. The first one is executed if the condition is satisfied and the second is executed if the condition is not satisfied. Only one of the command strings will be executed. After execution of the appropriate command string, control will continue with the first command after the apostrophe (unless the command string caused a branch out of the conditional to occur), since execution of the vertical bar command {\tt |} causes TECO to scan to the next matching apostrophe. Conditional commands are similar to the IF-THEN-ELSE constructs that you find in other structured programming languages, although none can match the brevity and elegance of TECO's implementation. Nonetheless, you must use these facilities wisely. Good programming practice dictates that a branch into the range of a conditional (from outside that range) should not occur. Conditional execution commands may be nested in the same manner as iteration commands. That is, the command string which is to be executed if the condition on {\tt n} is met may contain conditional execution commands, which may, in turn, contain further conditional execution commands. \begin{table}[h] \caption{\bf{Conditional Execution Commands}} \label{Conditional Execution Commands} \end{table} \nopagebreak \begin{list}{}{\labelsep 20pt} \item[{\em COMMAND}] {\em FUNCTION} \item[{\tt n"A}] Execute the following command string if {\tt n} equals the ASCII code for an alphabetic character (upper or lower case {\tt A} to {\tt Z}). \item[{\tt n"C}] Execute the following command string if {\tt n} is the ASCII code of any character that is a symbol constituent. This is usually one of the upper or lower case letters {\tt A} to {\tt Z}, one of the digits {\tt 0} to {\tt 9}, or period, or dollar sign, but may include additional characters on some operating systems. Consult the appropriate appendix. \item[{\tt n"D}] Execute the following command string if {\tt n} equals the ASCII code for a digit ({\tt 0} to {\tt 9}). \item[{\tt n"E}] Execute the following command string if {\tt n} is equal to zero. \item[{\tt n"F}] Execute the following command string if {\tt n} is FALSE. Equivalent to {\tt n"E}. \item[{\tt n"G}] Execute the following command string if {\tt n} is greater than zero. \item[{\tt n"L}] Execute the following command string if {\tt n} is less than zero. \item[{\tt n"N}] Execute the following command string if {\tt n} is not equal to zero. \item[{\tt n"R}] Execute the following command string if {\tt n} equals the ASCII code for an alphanumeric (upper or lower case {\tt A} to {\tt Z} or {\tt 0} to {\tt 9}). \item[{\tt n"S}] Execute the following command string if {\tt n} is SUCCESSFUL. Equivalent to {\tt n"L}. \item[{\tt n"T}] Execute the following command string if {\tt n} is TRUE. Equivalent to {\tt n"L}. \item[{\tt n"U}] Execute the following command string if {\tt n} is UNSUCCESSFUL. Equivalent to {\tt n"E}. \ifnotintecoeight \item[{\tt n"V}] Execute the following command string if {\tt n} equals the ASCII code for a lower case alphabetic character (lower case {\tt A} to {\tt Z}). {\em [Not in TECO-8]} \item[{\tt n"W}] Execute the following command string if {\tt n} equals the ASCII code for an upper case alphabetic character (upper case {\tt A} to {\tt Z}). {\em [Not in TECO-8]} \fi \item[{\tt n"<}] Identical to {\tt n"L} \item[{\tt n">}] Identical to {\tt n"G} \item[{\tt n"=}] Identical to {\tt n"E} \end{list} \label{Retrieving Environment Characteristics} The following TECO commands return values of interest to users who want information about their current job, the operating system, their terminal, etc. All negative {\tt EJ} commands return an operating system dependent value. Consult the appendices for operating system unique commands. \begin{table}[h] \caption{\bf{Retrieving Environment Characteristics}} \label{Retrieving Environment Characteristics} \end{table} \nopagebreak \begin{list}{}{\labelsep 20pt} \item[COMMAND] FUNCTION \item[{\tt -1EJ}] Return a number representing the computer and operating system upon which TECO is currently running. This value has the form {\em 256m+n} where {\em m} is a number representing the computer in use and {\em n} is a number representing the operating system that is running. Current values of {\em m} and {\em n} are: \begin{tabular}{llll} \multicolumn{2}{c}{\em Computer (m)} & \multicolumn{2}{c}{\em Operating System (n)} \\ 0 & PDP-11 & 0 & RSX-11D \\ & & 1 & RSX-11M \\ & & 2 & RSX-11S \\ & & 3 & IAS \\ & & 4 & RSTS/E \\ & & 5 & VAX/VMS \\ & & & (compatibility mode) \\ & & 6 & RSX-11M+ \\ & & 7 & RT-11 \\ 1 & PDP-8 & 0 & OS/8 \\ 2 & DEC-10 & 0 & TOPS-10 \\ 3 & DEC-20 & 0 & TOPS-20 \\ 4 & VAX-11 & 0 & VAX/VMS \\ & & & (native mode) \\ \end{tabular} \item[{\tt 0EJ}] Returns a value equal to your job number. On single-user systems, this is always a 0. \item[{\tt 1EJ}] Returns a value equal to your console keyboard number (the keyboard you detached from if you are running detached). On single-terminal systems, this is always a 0. \item[{\tt 2EJ}] Returns a value equal to your operating system's user identification number. This may be called your {\em UIC}, {\em PPN}, Group, etc. under various operating systems. Consult the appendices for more information. \end{list} \begin{table}[h] \caption{\bf{Setting Environment Information}} \label{Setting Environment Information} \end{table} \nopagebreak \begin{list}{}{\labelsep 20pt} \iftecotenonly \item[{\tt n,1EJ}] Set the terminal number to receive output. This will not affect terminal input. Your job will remain attached to, or detached from, your terminal, whichever it was before. Output will only occur if the specified terminal is ASSIGNed with a monitor {\tt ASSIGN} command (you may \caret {\tt C}, issue that command and continue) and if your job has POKE privileges. This command also sets the terminal to be reattached if the set detach flag ({\tt 64\&ET}) is cleared. The reattaching operation requires {\tt [1,2]} or {\tt JACCT} privileges. {\em [TECO-10 only]} \item[{\tt n,2EJ}] Sets your {\tt [p,pn]} to {\tt n} where {\tt n} has the same format as the number returned by the {\tt 2EJ} command. Issuance of this command requires the appropriate privileges. {\em [TECO-10 only]} \fi \end{list}