# How to add a package but only if it is not already there?

**URL:** <https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674>\
**Category:** General Usage\
**Tags:** question\
**Created:** [November 4, 2019, 4:40am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674 "2019-11-04T04:40:29Z")\
**Posts on this page:** 20\
**Page:** 1

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**Author:** ![andromodon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andromodon/32/36457_2.png) [@andromodon](https://discourse.julialang.org/u/andromodon)\
**Post date:** [November 4, 2019, 4:40am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/1 "2019-11-04T04:40:29Z")

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Hi. I’m learning Julia for the first time. I’'m looking for a way to say in my program “If you don’t already have this package, then get it, but if you do, then just use it”. The issue is that if I just put Pkg.add(“DataStructures”), then it seems to re-load that package from the git repo on every execution (which is time-consuming). I just want it to load the package from cache or something, but if it isn’t there, then I want it to load it from the git repo. I assume this is a common issue. How do people get the “Only add if we don’t already have package” functionality in an easy way?

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**Author:** ![jling](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jling/32/212909_2.png) [@jling](https://discourse.julialang.org/u/jling)\
**Post date:** [November 4, 2019, 4:52am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/2 "2019-11-04T04:52:07Z")

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if this for your script and you just want to see if a package exists or not, [How to test if package is installed - #2 by fengyang.wang](https://discourse.julialang.org/t/how-to-test-if-package-is-installed/3508/2)

if you’re making a module with optional dependency, maybe you can try `Requires.jl`

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**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [November 4, 2019, 6:54am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/3 "2019-11-04T06:54:26Z")

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> [@andromodon](#):
>
> How do people get the “Only add if we don’t already have package” functionality in an easy way?

Define a project and let the resolver deal with it. See

[https://julialang.github.io/Pkg.jl/dev/creating-packages/](https://julialang.github.io/Pkg.jl/dev/creating-packages/)

but the whole manual is worth reading.

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**Author:** ![non-Jedi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/non-jedi/32/3645_2.png) [@non-Jedi](https://discourse.julialang.org/u/non-Jedi)\
**Post date:** [November 4, 2019, 1:28pm UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/4 "2019-11-04T13:28:17Z")

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Even with Projects, for distributing _programs_ it would be nice if there was a way of checking whether the project has been instantiated yet (I’m actually thinking about the `eglot-julia` package I’ve been semi-working on). Do you know of a good way of doing this?

Just running `Pkg.instantiate()` every time isn’t a good solution since it makes network calls to update the registry.

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**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [November 4, 2019, 1:37pm UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/5 "2019-11-04T13:37:24Z")

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I am not aware of a recommended way (a lot of nuts and bolts for distributing Julia programs are WIP), but I would either

1. just make it part of an install script,

2. check for the depot being populated (since I would presumably have the program in its own depot).

3. check for the existence of a file which `touch` should just create when instantiating.

All of these are hacks though 😉

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**Author:** ![non-Jedi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/non-jedi/32/3645_2.png) [@non-Jedi](https://discourse.julialang.org/u/non-Jedi)\
**Post date:** [November 6, 2019, 6:34pm UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/6 "2019-11-06T18:34:21Z")

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Could you elaborate on how and why you use depots other than the default? The only reason I can come up with is as a hack to avoid precompiling when switching environments. I haven’t used anything but the default depots yet and hadn’t planned on doing so for the eglot-julia integration package.

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**Author:** ![ffevotte](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ffevotte/32/6587_2.png) [@ffevotte](https://discourse.julialang.org/u/ffevotte)\
**Post date:** [November 6, 2019, 9:51pm UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/7 "2019-11-06T21:51:09Z")

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> [@non-Jedi](#):
>
> Could you elaborate on how and why you use depots other than the default?

**How:**  
Setting the `JULIA_DEPOT_PATH` environment variable is a convenient way for me (Linux). There might be others

**Why:**  
When I do it, it’s usually to test whether something (a global thing, like a workflow; not just a given project) works in a pristine environment.

I once tried to maintain a specific depot, dedicated to providing the very specific versions of packages needed for LSP-related stuff to work. That experiment ended relatively uickly (mostly because of LSP stuff not being stable enough for my taste; not because it was a bad idea to have a depot for this).

There might very well be other good reasons to have specific depots.

  

> [@non-Jedi](#):
>
> for distributing _programs_ it would be nice if there was a way of checking whether the project has been instantiated yet

Not sure if it’s useful / clean, but I have this function in some scripts that I use to setup new environments:

```julia
tryusing(pkgsym) = try
    @eval using $pkgsym
    return true
catch e
    return e
end

```

```julia
julia> tryusing(:LinearAlgebra)
true

julia> if tryusing(:Foo) !== true
         println("Foo is not installed")
       end
Foo is not installed

```

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<div class="post-metadata">

**Author:** ![non-Jedi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/non-jedi/32/3645_2.png) [@non-Jedi](https://discourse.julialang.org/u/non-Jedi)\
**Post date:** [November 6, 2019, 9:55pm UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/8 "2019-11-06T21:55:34Z")

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> [@ffevotte](#):
>
> Not sure if it’s useful / clean, but I have this function in some scripts that I use to setup new environments:

This is more or less what I ended up doing.

> [@Using LanguageServer.jl with eglot in emacs](https://discourse.julialang.org/t/using-languageserver-jl-with-eglot-in-emacs/23125/38):
>
> LanguageServer.jl eglot integration is now packaged up at [https://github.com/non-Jedi/jleglot](https://github.com/non-Jedi/jleglot) and I just created a pending PR to melpa at [https://github.com/melpa/melpa/pull/6531](https://github.com/melpa/melpa/pull/6531). Hope it’s helpful to y’all. slight_smile For anyone wondering how I ended up making sure the project was instantiated, I stole a page from the Revise playbook: try @eval using LanguageServer catch @warn "Unable to import LanguageServer. Instantiating project." Pkg.instantiate() @eval using LanguageS…

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**Author:** ![ffevotte](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ffevotte/32/6587_2.png) [@ffevotte](https://discourse.julialang.org/u/ffevotte)\
**Post date:** [November 6, 2019, 9:58pm UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/9 "2019-11-06T21:58:12Z")

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> [@non-Jedi](#):
>
> This is more or less what I ended up doing.

Yes, I just saw that. Sorry for the noise 😔

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**Author:** ![00vareladavid](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/00vareladavid/32/23521_2.png) [@00vareladavid](https://discourse.julialang.org/u/00vareladavid)\
**Post date:** [November 7, 2019, 1:28am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/10 "2019-11-07T01:28:18Z")

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If I understand your question correctly, `Pkg.add("DataStructures")` already does what you request automatically.

The packages used by any of your projects are shared in the depots (e.g the “~/.julia” folder) so no unnecessary duplication occurs. If someone runs `Pkg.add("DataStructures")` and the package version already exists in your filesystem, `Pkg` will just use the existing package.

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**Author:** ![ffevotte](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ffevotte/32/6587_2.png) [@ffevotte](https://discourse.julialang.org/u/ffevotte)\
**Post date:** [November 7, 2019, 8:00am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/11 "2019-11-07T08:00:11Z")

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> [@00vareladavid](#):
>
> The packages used by any of your projects are shared in the depots (e.g the “~/.julia” folder) so no unnecessary duplication occurs. If someone runs `Pkg.add("DataStructures")` and the package version already exists in your filesystem, `Pkg` will just use the existing package

All that is true, but this primarily aims at avoiding unnecessary filesystem space usage. But I don’t think it to be the main concern here: when `Pkg.add` is issued, there is a lot more going on:

- the registry is updated
- if a new version of the package is available, this new version is downloaded and installed [EDIT: this is not true; see below]
- manifest / project files are updated [EDIT: if needed]

All this takes time, especially when network access is needed. A more minimalistic way of doing things would be:

1. if the package is already listed in Package.toml → do nothing
2. otherwise, if the package is already installed somewhere in the system → just update Package.toml + Manifest.toml
3. otherwise, update the registry, find the newest version available and install it

I might read it wrong, but I guess that is more the spirit of this thread. Doing things this way is probably not advisable in general, especially since you may end up with a very old version of your dependency. But there are cases where this would be useful. The situation described by `non-jedi` is a good example of that IMO. And the solution used in eglot in the post linked above implements point 1. in my list.

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**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [November 7, 2019, 9:31am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/12 "2019-11-07T09:31:45Z")

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> [@ffevotte](#):
>
> - the registry is updated
> - if a new version of the package is available, this new version is downloaded and installed
> - manifest / project files are updated

Since the second bullet is wrong, the last bullet is also wrong. What we could change is perhaps to move the updating of registries later.

See also [Offline mode by fredrikekre · Pull Request #1265 · JuliaLang/Pkg.jl · GitHub](https://github.com/JuliaLang/Pkg.jl/pull/1265) which basically implements your suggestion.

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**Author:** ![ffevotte](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ffevotte/32/6587_2.png) [@ffevotte](https://discourse.julialang.org/u/ffevotte)\
**Post date:** [November 7, 2019, 9:42am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/13 "2019-11-07T09:42:04Z")

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> [@fredrikekre](#):
>
> Since the second bullet is wrong,

Ah, sorry, I didn’t know. Why is it needed for Pkg to update the registries, if not in order to find whether a new version of the package is available?

> [@fredrikekre](#):
>
> the last bullet is also wrong

I might not have been clear: what I meant to say in this bullet is that, in general, `Pkg.add` updates `Project.toml` in order to list the new dependency, and also updates `Manifest.toml`. That’s the whole point of `Pkg.add`, right?

But yes, of course, if the package was already listed as a dependency and no new version was installed, no update is done to these files.

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**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [November 7, 2019, 9:44am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/14 "2019-11-07T09:44:17Z")

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> [@ffevotte](#):
>
> Why is it needed for Pkg to update the registries, if not in order to find whether a new version of the package is available?

It is not needed in the case where the package is already installed, thats why I suggested this

> [@fredrikekre](#):
>
> What we could change is perhaps to move the updating of registries later.

> [@ffevotte](#):
>
> I might not have been clear: what I meant to say in this bullet is that, in general, `Pkg.add` updates `Project.toml` in order to list the new dependency, and also updates `Manifest.toml` . That’s the whole point of `Pkg.add` , right?

Well sure, but how else should we record that we updated the dependencies?

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**Author:** ![ffevotte](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ffevotte/32/6587_2.png) [@ffevotte](https://discourse.julialang.org/u/ffevotte)\
**Post date:** [November 7, 2019, 9:59am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/15 "2019-11-07T09:59:26Z")

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> [@fredrikekre](#):
>
> What we could change is perhaps to move the updating of registries later.

By “later”, do you mean:

- “later within the series of operations performed by `Pkg.add`”, or
- “later when it will be needed by another `Pkg.add` or `Pkg.update` command” ?

> [@fredrikekre](#):
>
> Well sure, but how else should we record that we updated the dependencies?

Again, sorry if I’m not clear: of course it’s the whole point of `Pkg.add` to manage dependencies and record what’s done in `Project.toml` and `Manifest.toml`. And I’m very happy with it (and I venture to say everybody is 🙂 ).

The only issues I had were with my first two bullet points. To be clear: I happily use `Pkg.add` in order to get the benefit of the third bullet point (update `Project.toml`), and I would be even more happy if this operation involved as few side effects as possible.

Out of the two side effects I had issues with, it turns out that:

- updating the registry is not really needed and there is already work under way to avoid it when possible → thanks !
- there is actually no package update triggered and I didn’t have the problem I thought I had.

So everything is fine 🙂 Thanks for your work on `Pkg`, and sorry if I contributed to spread misconceptions about it

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**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [November 7, 2019, 10:01am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/16 "2019-11-07T10:01:07Z")

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> [@ffevotte](#):
>
> By “later”, do you mean:
> 
> - "later within the series of operations performed by `Pkg.add` ", or
> - “later when it will be needed by another `Pkg.add` or `Pkg.update` command” ?

I mean that we can do the check if the package exist before updating the registry.

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**Author:** ![ffevotte](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ffevotte/32/6587_2.png) [@ffevotte](https://discourse.julialang.org/u/ffevotte)\
**Post date:** [November 7, 2019, 10:09am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/17 "2019-11-07T10:09:32Z")

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> [@fredrikekre](#):
>
> I mean that we can do the check if the package exist before updating the registry.

and not update the registry if the package exists?

This would be great! Is that implemented in the PR you mentioned above? If not, do you think it could be implemented in a new PR, by someone (like me) who does not know (yet!) the internals of `Pkg`?

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**Author:** ![fredrikekre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/fredrikekre/32/1688_2.png) [@fredrikekre](https://discourse.julialang.org/u/fredrikekre)\
**Post date:** [November 7, 2019, 10:14am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/18 "2019-11-07T10:14:58Z")

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> [@ffevotte](#):
>
> and not update the registry if the package exists?

Yea.

> [@ffevotte](#):
>
> This would be great! Is that implemented in the PR you mentioned above? If not, do you think it could be implemented in a new PR, by someone (like me) who does not know (yet!) the internals of `Pkg` ?

No its not, and yea sure, should not be that hard.

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**Author:** ![ffevotte](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ffevotte/32/6587_2.png) [@ffevotte](https://discourse.julialang.org/u/ffevotte)\
**Post date:** [November 7, 2019, 10:56am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/19 "2019-11-07T10:56:17Z")

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OK, I’ll add it to my TODO list, then.

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**Author:** ![andromodon](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andromodon/32/36457_2.png) [@andromodon](https://discourse.julialang.org/u/andromodon)\
**Post date:** [November 8, 2019, 1:11am UTC](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674/20 "2019-11-08T01:11:47Z")

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Pkg.add(“DataStructures”) takes way too long to be run every time the program starts. Here’s an example:

[andromodon@yogie ~]$ time julia -e ‘using Pkg; Pkg.add(“Luxor”)’  
Updating registry at `~/.julia/registries/General`  
Updating git-repo `https://github.com/JuliaRegistries/General.git`  
Resolving package versions…  
Updating `~/.julia/environments/v1.2/Project.toml`  
[no changes]  
Updating `~/.julia/environments/v1.2/Manifest.toml`  
[no changes]

real 0m33.726s  
user 0m2.626s  
sys 0m0.387s

33 seconds!

What I’m wanting is a want is a use\_and\_add\_first\_if\_needed (I welcome better names. 😉 ) Ideally, “using” would just add automatically, or maybe there would be a flag that we could apply to julia to auto-add packages that are missing. Or, if there was a way to make Pkg.add take a few miillisconds that would work too. I feel like it should just return right away (Oops, nothign to do… we already have that), and wait for an Pkg.update to actually do network calls and update repos, etc.

[Next page](https://discourse.julialang.org/t/how-to-add-a-package-but-only-if-it-is-not-already-there/30674.md?page=2)