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Resolve variable inside another variable

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# 1  
Old 08-07-2012
Bug Resolve variable inside another variable
Hello Everyone,

I am trying to resolve a variable inside another variable.Let me go straight to the example.

Code:
Input:

Query=$Table_1 Join $Table_2

(Query itself is a variable here)

Now for two different cases I am assigning different values to Table_1 and Table_2

Code:
Case 1:
Table_1=tbl1_c1
Table_2=tbl2_c1

After this I want to write a command here so that when I echo Query it should show like:

Code:
echo $Query

tbl1_c1 Join tbl2_c1

I suppose this can be done with eval , and I have tried few options as well but I could not achieve the desired output.

Could you please help.

Thanks,
Vinay
# 2  
Old 08-07-2012
This won't work for you?
Code:
Table_1=tbl1_c1
Table_2=tbl2_c1
Query="$Table_1 Join $Table_2"
echo "$Query"

This User Gave Thanks to bartus11 For This Post:
vinay4889
# 3  
Old 08-07-2012
I'm not quite sure what the issue you're having is. It seems the solution Bartus posted should work. For funsies though, you could probably do it like this:

Code:
(19:12:02\[root@DeCoBoxOmega)
[~/Desktop]$ tables=( "tb1|tb2" "tb3|tb4") #create an array with pairs of tables

(19:12:10\[root@DeCoBoxOmega)
[~/Desktop]$ echo "${tables[0]%%|*}" #use string manipulation to play around with one
tb1

(19:12:26\[root@DeCoBoxOmega)
[~/Desktop]$ echo "${tables[1]##*|}" #Or the other
tb4

(19:12:34\[root@DeCoBoxOmega)
[~/Desktop]$ query="${tables[0]%%|*} Join ${tables[1]##*|}" #Use these arrays to create a variable

(19:12:46\[root@DeCoBoxOmega)
[~/Desktop]$ echo ${query} #and bob's your uncle
tb1 Join tb4

(19:12:50\[root@DeCoBoxOmega)
[~/Desktop]$

This User Gave Thanks to DeCoTwc For This Post:
vinay4889
# 4  
Old 08-07-2012
Hi
Maybe that's what you mean ?

Code:
$ Table_1=tbl1_c1
$ Table_2=tbl2_c1
$ Query='$Table_1 Join $Table_2'
$ echo $Query
$Table_1 Join $Table_2
$ eval echo $Query
tbl1_c1 Join tbl2_c1

This User Gave Thanks to Chirel For This Post:
vinay4889
# 5  
Old 08-08-2012
Thanks everyone for helping me understand the basics.I used m_eval option and it worked.

I will try out other options as well and will get back if there is any problem.

Thanks again.
# 6  
Old 08-08-2012
eval is a giant security hole.

If `rm -Rf ~/` ends up in your variables somehow, eval will execute it.

Please explain what you're actually trying to do so we can show you how to avoid the eval.
# 7  
Old 08-09-2012
Corona,

I wanted to resolve a variable (say Table_1) which again is inside another varible (say Query = $Table_1 Join).Using double quotes (") I was able to it it for sample examples.

Now when I try to implement the same in the actual problem statement I have, it throws error.

Code:
 
Code:
 
resolvedQuery=echo "$mainQuery"
 
Error:
 
varibale_test.ksh[40]: <big variable name here> : name too long

And yes actually variable here is big. It is a sql query.

I tried below as well.

Code:
 
resolvedQuery=$( eval echo $(echo $mainQuery))

This works well , only problem is single quote characters are dissolved after resolution.

Example:

Code:
 
Query= $Table_1 Join $Table_2 where condition='abc'

After resolution it becomes:

Code:
 
Query=t1 Join t2 where condition=abc

Can you please help me find a way , to resolve big length variable keeping single quote (') intact.

Thanks,
Vinay
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