What's the difference between eval and exec

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eval will run the arguments as a command in the current shell. In other words eval foo bar is the same as just foo bar. But variables will be expanded before executing, so we can execute commands saved in shell variables

 exec does not create a new process. It replaces the current process with the new command. If you did this on the command line then it will effectively end your shell session (and maybe log you out or close the terminal window!)

 
$ eval x=42
$ echo $x
42
$ exec x=42
bash: exec: x=42: not found

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