perlancar:

In the case of input validation, I usually let the variable name express the intent then validate the value into submission before doing the work:

sub frob_file {
    my $frobbable_filename = shift;
    die "Error" if !-e $frobbable_filename or -d $frobbable_filename;
    die "Nope!" if not_frobbable($filename);

    ... frob file ...
}
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In other cases when the variable isn't so clear but it will be clear shortly, I'll often use $t or $tmp for the placeholder. Then I'll give it a name or pass the data off to a better-named thing:

sub zap_the_thing {
    my $t = shift;
    my @files_to_zap;

    if (-d $t) {
       zap_dir($t);
    }
    else {
       push @files_to_zap, $t;
    }

    ... yadda ...

    zap_files(@files_to_zap);
}
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I don't think $t or $tmp is a great name, but finding good names is hard. I use it so that I can look at it and dispose of it ASAP.

Frequently I find I can't name something well the first time I encounter or use it. So I come up with my best guess of the name and use it. Then, when it feels like the name is wrong, and I find it doesn't fit, I do one of two things: If I have a better name in mind, I'll rename it. Sometimes, though, I can't think of a better name, so I instead give it a prefix of 'z' to "call it out". That way, when I revisit the code, I know I need a better name. Not perfect, not even good, but it usually gets me by. Yet I still wind up with stuff like:

# ?NEED GOOD NAME?
# If a group (Row, Col, Blk) has only one slot for a particular value,
# solve that cell.
sub solve_v_in_only_one_cell_in_R_C_B {
    my ($self, $GEN) = @_;
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an atrocity which came directly off my screen from last nights session.

...roboticus

When your only tool is a hammer, all problems look like your thumb.