[Info-vax] Long uptime cut short by Hurricane Sandy

[Stephen Hoffman]

On 2013-02-03 05:38:26 +0000, AEF said:

> I tried to write a script once that changed directory. It didn't work.
> Why? Because it forked itself to oblivion. I was told to try it with a
> period and a space in front it.

The leading dot-and-space syntax is shell shorthand for the shell's 
source command.  This command causes the script to run in the current 
process environment, and not in its own shell.

In VMS terms, you created a subprocess, issued a SET DEFAULT or 
possibly defined some symbols or some process logical names, and got 
nothing back when the subprocess exited; no changed default, no symbols 
and no logical names.   This is analogous to the difference between the 
SPAWN @mumble command and the @mumble command in DCL.

Here's a sequence that creates a script that uses cd to change the 
default directory of the current process.

$ cat z.z
#!/bin/bash
cd ~/foo
$ chmod o+x z.z
$ alias foo=.\ ~/z.z
$ foo

This sequence is similar to setting up a DCL foreign command for a 
procedure, though with the added detail of making the script 
executable.   In this case, this is also very close to the DCL command:

$ FOO :== SET DEFAULT yourloginroot:[foo]

You could also use

$ alias foo=source\ ~/z.z

in the above script, to make what's going on a little more verbose.

Yes, I do believe I've mentioned bash is cryptic.

The sethost script <http://labs.hoffmanlabs.com/node/1831> that I'd 
mentioned in a recent post is an example of using a script to shorten 
up common commands, too.

> Fine, but something else broke. I
> figured I should try it another time. And even if I write such a
> thing, I have to copy it to hundreds of servers running various
> versions of Solaris and Red Hat.
> 
> I've been using the ^R trick lately, so that helps. Still a far cry
> from TO.COM.

^S and ^R fall out of what readline provides.  There are a number of 
other features used for rummaging the history.  On BSD, see the 
editline stuff.  Also set vim or emacs or nano or whatever you'd prefer 
as your editor, and cause the shell to use the same control sequences 
as your editor.  And you'll probably want to configure and use command 
completion, too.

>> In aggregate, this isn't much different from having what TO.COM
>> provides, though the details do differ.
> 
> It's far less.

Caveat: not having used TO.COM and having just looked at the 
description from the Freeware, writing what TO.COM is documented to 
provide looks to be a SMOP in the shell, though that SMOP within the 
margin for error caused by some fundamental differences between OpenVMS 
and whichever Unix you're using.  A Unix system doesn't typically have 
a direct analog of an OpenVMS logical name, for instance.

These differences get back to the "don't automatically try to use the 
same solution on different platforms, as that path often leads to 
frustration" discussion.  Or more succinctly, "VMS != Unix"

You can combine something like sethost with the z.z script shown above 
to get pretty close to what TO.COM provides.

Or switch the script to a bash script (or switch the shebang to invoke 
python, perl, php, ruby, scala or whatever, and use the alias and the 
script to translate that CSV or XML or whatever-format-file you're 
using the VT to cause the MicroVAX to boot VMS to invoke that DCL 
procedure to mung that text.  Or dispense with the command-line stuff 
entirely, and allow the boss to cut-n-paste the input data into a text 
box on some web server, and process it there.  Or get rid of the whole 
chain of tools and get rid of the spreadsheet, and move the tool 
owership, bug tracking and related details into the same database, and 
all with a web UI and possibly with local clients for Android and iOS 
devices.

-- 
Pure Personal Opinion | HoffmanLabs LLC