In Linux Bash,
a1=web
a2=app
for counter in 1 2
do
a=a$counter
echo $[$a]
done
So,
$[$a]
How would it echo web & app?
1 Answer
What you are trying now works for integer-valued variables, because arithmetic expansion performs recursive expansion of strings as parameters until an integer value is found. For instance:
$ web=1
$ a=web
$ echo $[a]
1
$ echo $((a))
1
$[...] is just an obsolete form of arithmetic expression that predates the POSIX standard $((...)).
However, you are looking for simple indirect expansion, where the value of a parameter is used as the name of another parameter with an arbitrary value, rather than continuously expanding until an integer is found. In this case, use the ${!...} form of parameter expansion.
$ a=web
$ a1=a
$ echo $a1
a
$ echo ${!a1}
web
${!a}This is introduces a level of variable indirection.a*and nothing else matches, then you can simplify your code tofor each in ${!a*}; do echo ${!each}; done.