problem in retrieving value from a variable

lemon09 · 02-05-2010, 10:24 PM

Hello guys!!

In one of my scripts, I take input in the following manner

Code:

for i in $(seq $r)
   do
      for j in $(seq $c) 
	  do
	     read -p"a[$i][$j]=" a$i$j
	  done
   done

this code declares separate variables each time it enters the inner for loop.
Now the question is how shall I print each variable separately using a generalized form. I tried writing the following within a for loop

Code:

echo $(echo a$(echo $i)$(echo $j))

which did yield no result. So what shall I write?????

Please help!!!!

bmxcess · 02-05-2010, 10:55 PM

As far as I know bash only uspports one diimensional arrays. So try something like this in your loop.

Code:

Rows =  10 # number of rows in your array
let "index = $i * $Rows + $j"
a[$index]="some value"
# a[$i][$j]

then you can :

Code:

echo ${a[$index]}

catkin · 02-05-2010, 10:58 PM

In the statement read -p"a[$i][$j]=" a$i$j, a$i$j is evaluated and is used as the name of the variable used by the read command to store input. Here's an example command prompt session to illustrate that

Code:

c:~$ i=2
c:~$ j=5
c:~$ read a$i$j
my_input
c:~$ echo $i
2
c:~$ echo $j
5
c:~$ echo $a25
my_input

You can access such dynamically named variables in a script by using the eval command

Code:

eval echo \$a$i$j

The eval command instructs the shell to evaluate eval's arguments and then execute the resulting expression. Evaluating echo \$a$i$j results in echo $a25 (assuming $i has value 2 and $j has value 5). Note how the first $ is "escaped" with a \ to remove its special meaning during the first evaluation.

lemon09 · 02-05-2010, 11:18 PM

Thanks to both of you....

I shall remember what bmxcess has said....it was a good trick

As for Catkin, I know this could have been solved by 'eval'...but I don't want to use it...so can you just provide me with a substitute of it...I mean something like "$()".