Shell Programming and Scripting

Hi,

I have a k-shell master script which reads variables that are globally set and this script is modified by users per their requirements and users define few other variables.

In the script few expressions are evaluated which include both global variables and those added by the user, I would like to parse the expressions to get the list of variables used in the expression and check if they are set or not set before evaluating the expression.

The expressions are similiar to SQL where clause and I would like to know if there is any handy utility that parses the expressions and returns only the variables eliminating all constants, relational operators, arithmetic operators and logical operators ?

Give us something to parse. Some sample input and required output.

I would keep your master script somewhere that they cannot alter it else you will have a multitude of differences as people tweak the code about and a nightmare to debug. Assuming that each one has a separate home directory, could you get your script to use an input file in there?

You haven't given us anything to look at, but I would suggest something like this:-

Code:

#!/bin/ksh
# Any comments you want
# Change history perhaps

# Define standard settings
a=1
b=2
c=3

# Define user settings from user home directory file my_variables
. ~/my_variables

# Define defaults for unset variables
z1="${z1:-Hello}"
z2="${z2:=Here}"

# Define functions

# Main script processing
echo "Running with\n\ta=$a\n\tb=$b\n\tc=$c\n\tmy_var=$my_var\n\tz1=$z1\n\tz2=$z2"

exit

Does that give you a framework to start with?




Robin

Thank you for your replies

Below is a sample Expression

Code:

 
UsrAppNO=(UsrCustGBLNo*2) + UsrCustRegNo + 99

Actually there is a common global code over which regional customizations happen. In the above expression UsrCustGBLNo is set at global level and UsrCustRegNo at regional level and before I evaluate the expression I have to ensure all variables are set

To add to complexity some expressions are passed as arguments to few scripts so I am forced to look at a generic solution by parsing the input expression and get the variables and check if they hold a value.

The expressions contain relational,logical and arithmetic operators and constants

Thanks
Zulfi

Here are some more expressions

Are you saying that the people setting up their customised variables will be doing so free-form? I would be concerned that they will not process. What are you writing in and what would you expect to write in?

Would you expect to be able to recognise and process UsrAppNO=(UsrCustGBLNo*2) + UsrCustRegNo + 99 or could you set the rules? In ksh (like my example) this could be written as:-

Code:

((UsrAppNO=$UsrCustGBLNo*2)+$UsrCustRegNo+99))

Setting up a quick test, I got this:-

Code:

# UsrCustGBLNo=5
RBATTE1> UsrCustRegNo=10
RBATTE1> ((UsrAppNO=($UsrCustGBLNo*2)+$UsrCustRegNo+99))
RBATTE1> echo $UsrAppNO
119
RBATTE1>

Does that help?
Robin

Yes, the input expression has to be recognised and processed using expr. We are told that the expressions would be simple combinations of basic operators.

Thanks
Zulfi

Homework?