Installing command line tool if it's not in the PATH

Question

I have this bash function which I am trying to use to install a command line tool if it's not already in the PATH:

ncf(){

  if ! type -f ncf &> /dev/null || ! which ncf &> /dev/null; then

       echo "Installing NPM package '@oresoftware/ncf' globally...";

       npm i -s -g '@oresoftware/ncf' || {
         echo -e "Could not install NPM package '@oresoftware/ncf' globally." >&2
         echo -e "Please check your permissions to install global NPM packages." >&2
         return 1;
       }

  fi

  command ncf $@;
}

I have a couple of questions - is type -f ncf and which ncf redundant? Right now, I am checking to see if either of them exits with non-zero - if I either one does, I reinstall (at least that's what I think the code is doing).

My other question is - will &> work for bash versions older than 4, or other shells like sh, ksh, zsh, etc? Is there another construct I should use that's more cross platform than &>?

Would it not make sense to explicitly set the `PATH` in the script so that it includes the directory where the program _ought_ to be found? If that directory is not in `PATH`, you won't be able to start it no matter how much you install it. Also, quote `$@`, and you don't need `;` at the end of statements if there is no other statement afterwards on the same line. — Kusalananda, Jun 24 '18 at 12:23
@Kusalananda thanks, I have never figured out if I should quote "$@" or not. Why quote it? — Alexander Mills, Jun 24 '18 at 19:13
If you don't quote `$@`, the shell will perform word splitting and filename globbing on its individual elements. You should always quote all expansions (there only a couple of cases where you don't have to, but it's a good rule of thumb to do it everywhere). — Kusalananda, Jun 24 '18 at 20:33

Gilles 'SO- stop being evil' · Accepted Answer · 2018-06-24T20:30:17.660

1

which is redundant with type, except when it does the wrong thing altogether. Don't use which ever (except in ksh or zsh). Don't use type -f in portable sh, either: that's a ksh/bash extension. Just use plain type. If you want to look for an external command despite the presence of a function by the same name, you can use (unset -f ncf; type ncf).

To redirect the output away, use >/dev/null 2>&1. This can be abbreviated to &>/dev/null in ksh, bash and zsh, but not in plain sh.

  if ! type -f ncf >/dev/null 2>/dev/null; then …

edited Jun 24 '18 at 20:30

answered Jun 24 '18 at 10:26

Gilles 'SO- stop being evil'

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or `... >/dev/null 2>&1` will be portable too, won't it? – glenn jackman Jun 24 '18 at 10:33
@glennjackman Yes, that works too. It's actually closer to `&>/dev/null` since it only opens the file once, but for `/dev/null` that doesn't matter. – Gilles 'SO- stop being evil' Jun 24 '18 at 10:45
`unset -f ncf` right, not `unset ncf`? – Alexander Mills Jun 24 '18 at 19:10
What about using `command -v ncf`, is that better than `type -f`? – Alexander Mills Jun 24 '18 at 19:13
Because I am using `command ncf` to execute it, I would guess it makes the most sense to check if it doesn't exist by using `command -v ncf`? – Alexander Mills Jun 24 '18 at 19:16
@AlexanderMills `command -v ncf` prints `ncf` if `ncf` is a function. – Gilles 'SO- stop being evil' Jun 24 '18 at 20:31
I am more concerned about the exit code of `command -v` for this use case – Alexander Mills Jun 24 '18 at 21:32
@AlexanderMills `command -v ncf` prints `ncf` and exits with the status 0 if `ncf` is a function, regardless of whether an executable called `ncf` exists on the path. So you could use `(unset -f ncf; command -v ncf)` instead of `(unset -f ncf; )`, but this has no benefit, and you lose compatibility with some obscure but not antique shells (posh). – Gilles 'SO- stop being evil' Jun 25 '18 at 06:23
ahh I see, so `command -v` doesn't do what I want because it could succeed if there is a function in the shell but no corresponding executable in the PATH. I specifically need a check that ignores functions, because I don't really want to call `unset -f` beforehand if I don't have to. – Alexander Mills Jun 25 '18 at 06:26
So yes, unlike `command -v`, type -f does what I want because it ignores bash functions. – Alexander Mills Jun 25 '18 at 06:27

Installing command line tool if it's not in the PATH

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