Which of the following is not a valid command for variable declaration?

The command “newvar -x ENV_VAR=1” is not a valid command for variable declaration. The correct command for variable declaration and exporting it is the “export ENV_VAR=1” command.

The other options:

1. export ENV_VAR=1: This is a valid command for declaring a variable and exporting it.
2. typeset -x ENV_VAR=1: This is a valid command for declaring a variable and exporting it. In some shells, typeset is used instead of declare to define variables, and the -x flag indicates exporting.
3. declare -x ENV_VAR=1: This is a valid command for declaring a variable and exporting it. The -x flag is used to indicate exporting the variable.