The result is a Number, which is TRUE if {expr} is defined, zero otherwise.

Note: In a compiled :def function the evaluation is done at runtime. Use exists_compiled() to evaluate the expression at compile time.

For checking for a supported feature use has(). For checking if a file exists use filereadable().

The {expr} argument is a string, which contains one of these: varname internal variable (see dict.key internal-variables). Also works list[i] for curly-braces-names, Dictionary import.Func entries, List items, imported items, etc. Does not work for local variables in a compiled :def function. Also works for a function in Vim9 script, since it can be used as a function reference. Beware that evaluating an index may cause an error message for an invalid expression. E.g.:

                        :let l = [1, 2, 3]
                        :echo exists("l[5]")

                       0

                        :echo exists("l[xx]")

                       E121: Undefined variable: xx
                       0
    &option-name    Vim option (only checks if it exists,
                    not if it really works)
    +option-name    Vim option that works.
    $ENVNAME        environment variable (could also be
                    done by comparing with an empty
                    string)
    *funcname       built-in function (see `functions`)
                    or user defined function (see
                    `user-functions`) that is implemented.
                    Also works for a variable that is a
                    Funcref.
    ?funcname       built-in function that could be
                    implemented; to be used to check if
                    "funcname" is valid
    :cmdname        Ex command: built-in command, user
                    command or command modifier `:command`.
                    Returns:
                    1  for match with start of a command
                    2  full match with a command
                    3  matches several user commands
                    To check for a supported command
                    always check the return value to be 2.
    :2match         The `:2match` command.
    :3match         The `:3match` command (but you
                    probably should not use it, it is
                    reserved for internal usage)
    `#event`          autocommand defined for this event
    `#event#pattern`  autocommand defined for this event and
                    pattern (the pattern is taken
                    literally and compared to the
                    autocommand patterns character by
                    character)
    `#group`          autocommand group exists
    `#group#event`    autocommand defined for this group and
                    event.
    `#group#event#pattern`
                    autocommand defined for this group,
                    event and pattern.
    `##event`         autocommand for this event is
                    supported.

Examples:

exists("&shortname")
exists("$HOSTNAME")
exists("*strftime")
exists("*s:MyFunc")     " only for legacy script
exists("*MyFunc")
exists("bufcount")
exists(":Make")
exists("#CursorHold")
exists("#BufReadPre#*.gz")
exists("#filetypeindent")
exists("#filetypeindent#FileType")
exists("#filetypeindent#FileType#*")
exists("##ColorScheme")

There must be no space between the symbol (&/$/* /#) and the name. There must be no extra characters after the name, although in a few cases this is ignored. That may become stricter in the future, thus don't count on it! Working example:

exists(":make")

NOT working example:

exists(":make install")

Note that the argument must be a string, not the name of the variable itself. For example:

exists(bufcount)

This doesn't check for existence of the "bufcount" variable, but gets the value of "bufcount", and checks if that exists.

Can also be used as a method:

Varname()->exists()