Question

I have a environment config file where i have defined the environment variables. I use source to get these variables inside my shell script(bash).

I use a checkout command in my shell script which checks out the files from location defined in an environment variable. Now i need to use multiple locations to checkout the files which can be any number for different run of shell script.

For eg. User gives two paths, PATH1 and PATH2 in config file and a NUM_OF_PATHS as 2.

In my shell script I want to do something like below for using path.

i=0
echo ${NUM_OF_PATHS}
while [ $i -lt ${NUM_OF_PATHS} ]
do
    checkout $PATH{$i}
    i=`expr $i + 1`
done

How can I use the variable i to form an environment variable PATH1 or PATH2 etc.?

Answer 1

i=1
while [ $i -le ${NUM_OF_PATHS} ]
do
  CPATH=$(eval echo \$\{PATH$i\})
  echo "PATH$i: $CPATH"
  let i++ 
done

eval combines and evaluates its parameters and executes the combined expression. Here, eval executes: echo ${PATH1}. In order to do this, we first escape the ${...} so that echo can receive them after eval. The only un-escaped special character is $ before i. eval expands this and strips off the escaped characters and executes echo with the result.

So, CPATH=$(eval echo \$\{PATH$i\}) becomes CPATH=$(echo ${PATH1}) and CPATH gets the echo output.