TACL (programming language)

TACL (the Tandem Advanced Command Language) is the scripting programming language used in Tandem Computers.

Tandem Computers were originally designed and sold by Tandem Computers, Inc., based in Cupertino, CA. Tandem's strategy was the emerging concept of "continuous availability" that relied on redundant hardware and a well engineered operating system (NonStop Kernel or NSK) to ensure continuous application availability by ensuring the system could survive any single point of hardware failure.

The paragraph above describes the philosophy behind the design of the hardware and the software. Upon that NSK platform there are two programming languages at least - TAL as the compiled language, and TACL as the interpreted language. NSK has compilers for most useful languages too. TAL is rumoured to be about to be deprecated, but TACL remains as the default scripting language on these machines. HP provide a Korn-based shell command interface also these days, but it does not offer all that TACL does for NSK sysadmins - for instance, the netstat command has not been implemented. TACL builtins reflect the multi-CPU nature of NSK, and there probably isn't much more to say than that - if you fully understand all the TACL builtins then you are probably well on the way to understanding the NSK.

TACL continues to be the scripting language used on Hewlett Packard NonStop Servers. NonStop servers are key components of the backbone infrastructure of the largest banks, casinos, retailers, telephone companies, email systems and stock exchanges worldwide.

TACL is interpreted. TACL instructions can be stored in a simple text file as MACROS, ROUTINES, or DEFINES to make scripts. Such scripts are often used to store complex configuration instructions such as start-up and hardware configuration sequences.

The TACL language has a large number of Built-in utilities which allow the user to capture output from various system utilities and parse the captured text, line by line or character by character. This allows users to build TACL programs that can monitor system events through the use of filters that monitor the system and application event logs.

Example of a TACL routine saved in the file FILE1:

?Section HELLO_BERNARD ROUTINE

#OUTPUT Hello BERNARD

How to run the TACL routine:

1. From a TACL prompt type: LOAD / KEEP 1 / FILE1 (this loads the routine into memory)

2. Type: HELLO_BERNARD to run the routine

3. Output will be: Hello BERNARD

Or create a file named FILE1 and add the following two lines:

?TACL ROUTINE

#OUTPUT Hello BERNARD

Execute the routine by naming the file at the tacl prompt:

> RUN FILE1