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'

829,060

1

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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