5 PECS (Pluggable Environment Contribution System)

5.1 USER ENVIRONMENT SETTINGS

PECS supports personal settings for the following types of settings:

- environment variables

- X resources

- GUI root window menu items

- shell aliases

All personal settings belong in files in the ~/.pecs directory, which should exist and contain (comments-only) example files. The big problem with putting a setting in one of these files, is knowing which file to put it in! This section explains the steps to determine where to put a setting:

1. Decide the 'type' of the setting

Four 'types' of personal settings are supported by PECS:

a. environment variables (type=env)

b. X resources (type=xrdb)

c. GUI root menu items (type=wmrc)

d. shell aliases (type=ali)

Note down what 'type' it is.

2. Decide the 'application-scope' of the setting

Settings either:

a. relate to a PECS-aware application (application-scope=apps)

(e.g. VLTROOT, INTROOT, GNU_ROOT, NOCCS, PRINTER, RTAP_EXISTS)

b. don't relate to a PECS-aware application (application-scope=misc)

(e.g. DFLOW_ROOT because it relates to older versions of VLTSW only, NNTPSERVER, LESS, MAIL, PATH=$HOME/bin:$PATH).

3. Decide the 'host-scope' of the setting

Settings either:

a. are applicable only on certain hosts (host-scope=<name-of-host>)

b. are applicable on all hosts (host-scope=all)

4) Put the setting in the right file

Now that you've worked out the three attributes 'type', 'application-scope' and 'host-scope', it's easy; the setting belongs in the file:

~/.pecs/<application-scope>-<host-scope>.<type>

e.g., to change your prompt set 'PS1' in ~/.pecs/apps-all.env, and

to change your VLTROOT set VLTROOT in the same file.

5) Activating the setting

To activate the change in setting first run:

make_xdefaults

and then log out and back in.

Let's look at a couple of examples; consider each of the following

settings, look at the values it has for each attribute, and see the

name of the file it goes in.

Example #1: Changing VLTROOT

Suppose you're working on a machine where VLTROOT is set to /vlt/MAR2001/CCS, and you need to point it at FEB2000 instead just for a quick test. Well,

it's an environment variable (type=env)

it relates to VLTSW, which is a PECS-aware application (application-scope=apps)

you only need it for a quick test on host 'te13' (host-scope=te13)

So, having worked that out, the setting belongs in the file:

~/.pecs/apps-te13.env

So, in the file you just put:

VLTROOT=/vlt/FEB2000/CCS

Note that environment variables supported by a PECS-aware application are automatically made available to sub-processes ('exported') so you do not need to export it yourself (though it does no harm to do so).

Example #2: the 'which' alias

Yes, the 'which' command under Bourne-like shells does not work quite the same as it did under Tcsh. Under Bash, the nearest equivalent to 'which' is 'type' or 'type -all'. So to make 'which' an alias for 'type -all':

it's a shell alias (type=ali)

it's not related to a PECS-aware application, it's just personal setting (application-scope=misc)

you want it everywhere (host-scope=all)

So, having worked that out, the setting belongs in the file:

~/.pecs/misc-all.ali

So, in the file you just put:

alias which='type -all'

Aliases are read per-shell-process, so it is not necessary to log out; your next new xterm will see the alias.

Note that Bash aliases have an '=' between the alias and its value, unlike Tcsh.

Example #3: you want to add 'top' and 'xv' to your 'User Menu'

PECS provides a GUI root window sub-menu entitled 'User Menu'. Suppose you want to create the menu to contain the command

'top'

it's a GUI root window menu item (type=wmrc)

it's not related to a PECS-aware application (the user menu never is) (application-scope=misc)

you want to see this menu everywhere (host-scope=all)

So, having worked that out, the setting belongs in the file:

~/.pecs/misc-all.wmrc

So, in the file you put:

Menu user_menu

{

"My Menu" f.title

"Top" f.exec "xterm -T top -n top -e top"

"Xv" f.exec "xv"

}

Note that 'top' isn't on all systems, so simply calling 'top' is a bit naive.

To activate the settings select 'Restart' from the GUI root window menu.

Example #4: you don't like the Xclock updating every second

PECS allows you to specify new values for X resources, but it also allows you to 'unset' existing ones (this is not a standard behaviour of X).

You will probably find your Xclocks showing a second hand, because of the X resource:

XClock*update: 1

To cancel this setting, just provide a blank value for it. So,

it's an X resource (type=xrdb)

it's related to a PECS-aware application (yes, this resource is defined by VLTSW)

(application-scope=apps)

you want to see this menu everywhere (host-scope=all)

So, having worked that out, the setting belongs in the file:

~/.pecs/apps-all.xrdb

So, in the file you put:

XClock*update:

To activate the change you need to log out and log in again.

Example #5: you don't like to use

"export VARIABLE=VALUE"

and you want to keep using

"setenv VARIABLE VALUE"

Very bad idea, but if you are so obstinate, you should write a function, because aliases which require embedded parameters must be written as functions, but should still be put in the ".ali" file. Here's an example:

export_function()

{

export $1=$2

}

alias setenv=export_function

5.2 A CRASH-COURSE IN BOURNE SHELL

What follows is a little cookbook of common things you may wish to put in your ~/.pecs/*.env files:

To set a variable do this:

VARIABLE1=value

VARIABLE2="value with spaces"

export VARIABLE1 VARIABLE2

(Notice there are no spaces around the '='; bourne shell is sensitive

about this.)

To safely test if a variable is set do this:

if [ "X$VARIABLE" != X ]; then

code to do if VARIABLE is set

else

code to do if VARIABLE is not set

fi

To set an alias, put something like this in your

~/.pecs/misc-all.ali file:

alias ALIASNAME="alias value"

(e.g: alias ls="/bin/ls -a")

A switch statement looks like this:

case "$VARIABLE" in

value1) do this

and then this

and this is last ;;

value2) do this

and something else ;;

*) this is the default action ;;

esac

If you want to do a tcsh rehash, you should do:

hash -r

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