Alias doesn't work inside a Bash script [duplicate]

Answer 1

Aliases are for the interactive shell, what you want here is a function, e.g.

#!/bin/bash
function my_command() {
    echo ok
}

my_command

Answer 2

From the bash man page:

Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see the description of shopt under SHELL BUILTIN COMMANDS below).

In other words, aliases are not enabled in bash shell scripts by default. When you run the script with bash, it fails.

Your sh appears to default to allowing aliases in scripts. When you run the script with sh, it succeeds.

./command.sh happens to work because your shebang is malformed (you're missing the ! in #!/bin/bash).