mshell has two variable namespaces: mshell variables (typed values stored in the interpreter) and environment variables (strings stored in the process environment). They use different sigils and behave differently.

mshell Variables § Back to top

Store a value with the ! suffix and retrieve it with @. Storing pops the top of the stack; retrieval pushes the stored value back onto the stack.

42 answer!
@answer 1 + total!
@total wl

Retrieving an unknown variable results in an error. Mshell variables do not consult the environment, so @name only looks in the mshell variable map.

Environment Variables § Back to top

Environment variables are accessed with $NAME. They are always strings. Use $NAME! to set them and $NAME? to check for existence. Reading a missing environment variable with $NAME is an error. Environment variables are always exported to subprocesses, so setting them affects subsequent command executions.

"info" $LOG_LEVEL!
$LOG_LEVEL wl

$EDITOR? if
    $EDITOR wl
else
    "vim" wl
end

You can print all environment variables (sorted by key) using the built-in .env function.

.env

"/tmp" $TMPDIR!
['my-tool']!

PWD and OLDPWD § Back to top

Changing directories updates PWD and OLDPWD in the environment. You can read them the same way as any other environment variable.

$PWD wl
`/tmp` cd
$OLDPWD wl