Shell Programming and Scripting

(copied directly from my other thread about something else)

At the moment, I just use...

cat config_file|grep var_name|cut -d'=' -f2

... which is fine for what I've been doing, but I'm not sure what to
do when there are a variable number of entries and I want it go through
them like a list.

Course, the config file itself could be a script but I prefer to keep
the configs seperate from the functions. Not really sure how to do
this. It's a problem sometimes, though I can usually hack up some kind
of work-around for my ignorance.

You don't need to use cat ... read useless use of cat (dont worry everyone has been there)

How about providing a sample of your config_file. Might be really helpfull.

I don't think there's a general best way. Personally, I prefer the way you seem to dislike, which is just sourcing a "script" which does nothing but define variables.

The big exception to this is when there's multiple targets, for example a connectivity check script that should treat different targets in different ways. The config would be something like

Code:

# This is a comment
# Host that's pingable
1.2.3.4|ping -c 3 -W 1 ${HOST}
# Host not pingable, but with a know port open
5.6.7.8|nc -w 3 -z ${HOST} 80

and read it like this:

Code:

grep -v '^#' ${config} | while IFS='|' read HOST COMMAND
do
    CMD=$( eval "echo $COMMAND" )
    $CMD
    if [ $? -eq 0 ]
.....
done

Don't put functions in your config files, then. :shrug: It's still the simplest and most direct way to do it, and the way its almost always done. You don't have to worry about comments or blank lines, the shell handles it.

Other alternatives usually involve eval which is, in the end, might as well just have sourced it since eval runs any shell statement, except that much harder for having to do all sorts of parsing yourself.

Interesting

So what do I use instead of cat for a line like this?

Code:

foo=`cat config_file|grep var_name|cut -d'=' -f2`

As to the question posting my config file, I don't have a specific one in mind. Something in another thread brought it to mind, and it's something I've been thinking about for a while.
------------------------------------------
As to the other comments:

Ok, I'll try doing it with scripts instead. The main config file I'm thinking provides variables for 17 different scripts (many of which both a) require the same variables and b) call eachother), so I'm not sure if it makes sense to have each of them loading all of the variables.,, I guess I could have any parent scripts load the proper variables into the sub-scripts... but some of them are called both independently and as a part of other operations. It's sort of complicated. since it's basically designed to shift my netbook between keyboard and tablet mode, and it manages all the settings for each mode, as well as things like rotating the screen and syncing the virtual keyboard with the screen orientation.

So far, I've just been "cat"ing all the required variables into each script as they are needed. I have no idea if this is the right way to do it. It's just what occured to me to do. That's sort of how all my scripting is. I just use the few commands I know to get the result I want. It usually works, but I'm sure there is all kinds of stupidity happening in the process(es?).

Code:

foo=$( grep var_name config_file | cut -d'=' -f2 )

Do it like it's usually done with headers in C: conditional includes

Code:

if [ -z $CONF_FILE_LOADED ]
then
    var1=value1
    var2=value2
....
    CONF_FILE_LOADED=1
fi

So no matter how often you source it, the variables are set only once.

Another way to read a variable:
Config file:

Code:

efs=123

script snippet:

Code:

IFS='='  #set Input Field Separator
grep efs config_file | read var_name var_value
print "Variable: ${var_name}  value: $var_value"

Output:

Code:

Variable: efs  value: 123