Substitution in shell script

Question

I like to evaluate the following in linux shell

CMD_6='ls'
CMD_7='ls -l'
VER=6
CMD="CMD_"$VER

I'm expecting $CMD to execute CMD_6 and list the directory content, but it is throwing an error:

-bash: CMD_6: command not found

Can someone explain how to do this substitution?

Answer 1

Use functions.

cmd_6 () { ls; }
cmd_7 () { ls -l; }
ver=6
cmd="cmd_$ver"
"$cmd"

The value of cmd shouldn't be any more complicated than a single function or command name: no arguments, no other shell syntax.

Answer 2

... or use aliases:

$ alias cmd_6='ls'
$ ver=6
$ alias cmd="cmd_$ver"
$ alias
alias cmd='cmd_6'
alias cmd_6='ls'

Answer 3

The other answers explain how to to it with functions and aliases, but it can be done with variables:

foo="ls -l" bar=/bin/bash
$foo $bar

Output:

-rwxr-xr-x 1 root root 1099016 May 17  2017 /bin/bash

---

But this is a little different:

CMD="CMD_"$VER

To run it, do:

eval \$$CMD

Be careful with eval , only feed it known or checked input.