Make a zip file in Elixir

Hris

Hello.
I have a text file and I want to make a zip file from it using Elixir or just to compress its folder.

files = File.ls!("path") 
           |> Enum.map(fn filename -> Path.join("path", filename) end)
           |> Enum.map(&String.to_charlist/1)

I then use :zip.create("foo.zip", files) to write the zip file. It returns a tuple: {:ok, "foo.zip"} but the file does not get saved.
Where is my mistake? Or can I get some sort of a solution? Thanks.

7 comments

#compression #zip

1 7831 7

2020-09-28 04:33:20 UTC

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NobbZ

The file is created in the working dir of the running BEAM VM, you can check with System.cwd/0.

Post #1

Qqwy

TypeCheck Core Team

And usually this is the folder that your ‘mix.exs’ is also in. If you are running in development that is.
When you have made a release, the folder location might be different.

Post #2

Hris

Okay, zip file is created but there is another problem. It writes the whole path to the file, for example “/home/user/project/text.txt” and not just the file. Is there any other way just to compress the text file without its path?

Post #3

lackac

According to the Erlang docs on :zip.create/3 there is an optional third argument with options where you could set the working directory for compression with [cwd: path]. The effect is that files will be looked up within that path and will omit the path in the compressed file.

Expanding on your example:

files =
  File.ls!(path)
  |> Enum.map(&String.to_charlist/1)

:zip.create("files.zip", files, cwd: path)

$ unzip -l files.zip
Archive:  files.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
   212151  09-22-2016 17:32   file1.txt
   333814  09-22-2016 17:32   file2.txt
   269066  09-22-2016 17:32   file3.txt
   333736  09-22-2016 17:32   file4.txt
   284213  09-22-2016 17:32   file5.txt
---------                     -------
  1432980                     5 files

Post #4

aligredo

Hello there, I’m new to elixir and when I wrote the same snippet I got the following warning:

The call zip:create(#{#<116>(8, 1, 'integer', ['unsigned', 'big']), #<101>(8, 1, 'integer', ['unsigned', 'big']), #<115>
(8, 1, 'integer', ['unsigned', 'big']), #<116>(8, 1, 'integer', ['unsigned', 'big']), #<46>(8, 1, 'integer', ['unsigned', 
'big']), #<97>(8, 1, 'integer', ['unsigned', 'big']), #<112>(8, 1, 'integer', ['unsigned', 'big']), #<107>(8, 1, 'integer',
 ['unsigned', 'big']), #<103>(8, 1, 'integer', ['unsigned', 'big'])}#,_files@1::[any()],[{'cwd',<<_:8,_:_*8>>},...]) will 
never return since the success typing is (atom() | [atom() | [any()] | char()],[atom() | [atom() | [any()] | char()] | 
{atom() | [atom() | [any()] | char()],binary()} | {atom() | [atom() | [any()] | char()],binary(),{'file_info','undefined' | 
non_neg_integer(),'device' | 'directory' | 'other' | 'regular' | 'symlink' | 'undefined','none' | 'read' | 'read_write' |
 'undefined' | 'write','undefined' | non_neg_integer() | {_,_},'undefined' | non_neg_integer() | {_,_},'undefined' |
 non_neg_integer() | {_,_},'undefined' | non_neg_integer(),'undefined' | non_neg_integer(),'undefined' | 
non_neg_integer(),'undefined' | non_neg_integer(),'undefined' | non_neg_integer(),'undefined' | 
non_neg_integer(),'undefined' | non_neg_integer()}}],['cooked' | 'memory' | 'verbose' | {'comment',string()} | 
{'compress','all' | [[any()]] | {'add',[any()]} | {'del',[any()]}} | {'cwd',string()} | {'uncompress','all' | [[any()]] | {'add',
[any()]} | {'del',[any()]}}]) -> {'error',_} | {'ok',atom() | [atom() | [any()] | char()] | {atom() | [atom() | [any()] | 
char()],binary()}} and the contract is (Name,FileList,Options) -> RetValue when Name :: file:name(), FileList :: 
[FileSpec], FileSpec :: file:name() | {file:name(),binary()} | {file:name(),binary(),file:file_info()}, Options :: 
[Option], Option :: create_option(), RetValue :: {'ok',FileName::filename()} | {'ok',
{FileName::filename(),binary()}} | {'error',Reason::term()}ElixirLS Dialyzer

any idea about why am I getting this?

Thanks in advance.

Post #6

SZJX

It seems that :zip.create expects Erlang string type which is actually charlist. So instead of "files.zip" you’d need to write something like 'files.zip'? Or is the conversion somehow performed automatically.

Post #7

NobbZ

You are right, this function still does require a char list (atoms/nested list), and no there is no automatic conversion between elixir strings or char lists.

Post #8

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