In Bash we can dynamically build and execute the commands. Below we can find two examples of building command stored in variable and then execute the commands to get result:

(1) eval - Build command and execute

cmd="echo Hello World!"
cmd_file="> out.txt"
eval ${cmd} ${cmd_file}

We build command: echo Hello World! > out.txt from two variables and then execute it with eval
The result is creating a new file out.txt and writing text: Hello World!

(2) $($cmd) - Execute command

cmd="ls -a"
echo $res

Alternative solution is to use $($cmd) to run a command which is stored in a variable. The result will be:

  • create variable with ls -a command
  • execute the command
  • print out the result

(3) Dynamically Build Command in script

cmd="ls -a"
echo $res

Saving the above as Next we can run the script by ./