Getting Started with coala

Welcome to this little tutorial. It is meant to be a gentle introduction to the usage of coala.


In order to complete this tutorial you will need coala installed. Installation instructions can be found here.


Here’s a list of our supported languages.

Get Some Code

In order to perform a static code analysis on your code you will need some code to check. If you do not have your own code you want to check, you can retrieve our tutorial samples:

git clone

Please note that the commands given in this tutorial are intended for use with this sample code and may need minor adjustments.

Let’s Start!

There are two options how to let coala know what kind of analysis it should perform on which code.

Command Line Interface

In order to specify the files to analyze, you can use the --files argument of coala like demonstrated below. For all file paths, you can specify (recursive) globs.

Because analysis routines can do many various things we named them bears. A bear can check your code for potential problems, calculate metrics and even provide corrections for your code.

You can specify the bears that you want coala to run using the --bears argument:

cd coala-tutorial
coala --files=src/\*.c --bears=SpaceConsistencyBear --save


You can use comma separated values to specify more than one item in arguments! Do not use spaces as that would start a new argument. Example: SpaceConsistencyBear,PEP8Bear

coala will now ask you for missing values that are needed to perform the analysis, which in this case is only the use_spaces setting. We recommend setting it to True.

Please enter a value for the setting "use_spaces" (True if spaces
are to be used instead of tabs.) needed by SpaceConsistencyBear
for section "cli"

coala will now check the code and, in case you use the tutorial code, yield one result. SpaceConsistencyBear will detect a trailing whitespace at the end of the line, after #include <stdio.h> in the main.c file. coala will then ask you to remove the trailing space, by applying the suggested patch (option 2).

Executing section cli...

|   1| #include·<stdio.h>·
|    | [NORMAL] SpaceConsistencyBear:
|    | Line contains following spacing inconsistencies:
|    | - Trailing whitespaces.
|----|    | /path/coala-tutorial/src/main.c
|    |++++| /path/coala-tutorial/src/main.c
|   1|    |-#include <stdio.h>
|    |   1|+#include <stdio.h>
|   2|   2|
|   3|   3| int main(void) {
|   4|   4|     printf("Welcome to coala. Keep following the
                tutorial, you are doing a great job so far!\n");
|    | *0: Do nothing
|    |  1: Open file(s)
|    |  2: Apply patch
|    |  3: Print more info
|    |  4: Add ignore comment
|    | Enter number (Ctrl-D to exit): 2

If the patch was applied succesfully, you should see something like this:

|    | Patch applied successfully.
|    | *0: Do nothing
|    |  1: Open file(s)
|    |  2: Print more info
|    |  3: Add ignore comment
|    | Enter number (Ctrl-D to exit):

Exit by pressing Ctrl-D.

You can also run coala in non interactive mode (given that all the settings required by the bears you are using are provided in the .coafile)

coala  --non-interactive

In this case there won’t be any interaction, the patch will be shown directly.

Feel free to experiment a bit. You’ve successfully analysed some code! But don’t stop reading - you don’t have to enter all those values again! We have given coala the --save argument, which means that it will automatically generate a .coafile into the current directory. Read on!

Configuration Files - coafiles

coala supports a very simple configuration file. If you’ve executed the instructions from the CLI section above, coala will already have such a file readily prepared for you. Go, take a look at it:

cat .coafile


If you are using Windows, you should use type .coafile instead!

This should yield something like this:

bears = SpaceConsistencyBear
files = src/*.c
use_spaces = True

If you now invoke coala it will parse this .coafile from your current directory. This makes it easy to specify once for your project what is checked with which bears and make it available to all contributors.

Feel free to play around with this file. You can either edit it manually or add/edit settings via coala --save ... invocations. If you want coala to save settings every time, you can add save = True manually into your .coafile.


Thats all nice and well but we also have a Makefile for our project we want to check. So let us introduce another feature of our configuration syntax: sections.

The line [cli] in the .coafile implies that everything below belongs to the special cli section. You may specify sections when you enter the settings via the Command Line Interface (CLI). You will soon learn all about them. When you don’t specify any sections, the settings will implicitly belong to the [cli] section.

Next you will see how to specify sections using the command line when you are running coala. Let’s check the line lengths of our Makefile:

coala -S Makefiles.bears=LineLengthBear Makefiles.files=Makefile --save

As you can see, the -S (or --settings) option allows to specify arbitrary settings. Settings can be directly stored into a section with the section.setting syntax.

By default, the LineLengthBear checks whether each line contains 79 chars or less in a line. To change this value, use the max_line_length inside the .coafile.

coala will now yield any result you didn’t correct last time, plus a new one for the Makefile. This time coala (or better, the LineLengthBear) doesn’t know how to fix the issue but still tries to provide as much helpful information as possible and provides you the option to directly open the file in an editor of your choice.


If you want to set a default editor and not be asked for one every time, you can simply add editor=$editorName (i.e. editor=vim) to your project’s .coafile and it will automatically open in that one.


If your editor is already open this may not work, because the other process will shortly communicate with the existent process and return immediately. coala handles this for some editors automatically, if yours does not work yet - please file an issue so we can include it!

If you changed one file in multiple results, coala will merge the changes if this is possible.

coala should have appended something like this to your .coafile:

bears = LineLengthBear
files = Makefile

As you see, sections provide a way to have different configurations for possibly different languages in one file. They are executed sequentially.


For a list of configuration options for the bears, take a look at our coala languages directory.

Auto-applying Results

Often you don’t want to look at trivial results like spacing issues. For that purpose coala includes a special setting called default_actions that allows you to set the action for a bear that shall be automatically applied on run. We have a command line alias --apply-patches to make it easier to use.

By using --apply-patches, the user does not have to press 2. (A)pply patch for applying a patch. Every patch is applied automatically. Alternatively, using the setting default_actions="*: ApplyPatchAction" will automatically apply --apply-patches on run.

Let’s automatically fix Python code. Take a look at our sample Python code:

$ cat src/

This is a simple library that provides a function that can add numbers.


def add(a,b):
    return a+b;

import sys

That looks horrible, doesn’t it? Let’s fix it!

$ coala -S python.bears=PEP8Bear python.files=\*\*/\*.py \
--apply-patches --save
# other output ...
Executing section cli...
Executing section python...
[INFO][11:03:37] Applied 'ApplyPatchAction' for 'PEP8Bear'.
[INFO][11:03:37] Applied 'ApplyPatchAction' for 'PEP8Bear'.

coala would now fix all spacing issues and without bothering you again.


When you try the above example, you may get a warning, saying that all settings in the cli section are implicitly inherited to all other sections (if they do not override their values). It also advises us to change the name of that section to avoid unexpected behavior. The next section explains what it means and how you can avoid it.

Setting Inheritance

Let’s first see what inheritance means.

Before proceeding, rename the cli section in the .coafile to all (we will soon explain the reason behind this change).

Lets add the following section to our .coafile:

bears = KeywordBear

And execute coala with the -s argument which is the same as --save. I recommend setting case insensitive keywords to TODO, FIXME and case sensitive keywords empty.

After the results we’ve already seen, we’ll see a new informational one which informs us that we have a TODO in our code.

Did you note that we didn’t specify which files to check this time? This is because all settings, including files = src/*.c, from the all section (previously called cli) have been inherited in the new TODOS section that we just added.

You can make a section inherit from any previously defined section using this syntax:



cli is an internally reserved section name. All of its settings are implicitly inherited to every other section by default. It is because of this implicit inheritance feature that we are adviced to rename the cli section to something else. Doing so will save us from having unexpected values of cli being implicitly inherited into our sections. We strongly suggest renaming it.

Ignoring Issues

There are several ways to ignore certain issues, so you aren’t lost if any routines yield false positives.

Ignoring Files

coala lets you ignore whole files through the ignore setting. In addition to normal globs, coala offers ** to match all directories and subdirectories:

files = **/*.h
ignore = **/resources.h

This configuration would include all header (.h) files but leaves out resource headers.

Ignoring Code Inside Files

Sometimes you need finer-graded ignores. Imagine you have a LineLengthBear that shall not run on some code segments, because you can’t wrap them:

code = "that's checked normally"

# Ignore LineLengthBear
unwrappable_string = "some string that is long and would exceed the limit"

You can also skip an area:

# Start ignoring LineLengthBear
unwrappable_string_2 = unwrappable_string + "yeah it goes even further..."
another_unwrappable_string = unwrappable_string + unwrappable_string_2
# Stop ignoring

You can also conditionally combine ignore rules! Bear names will be split by comma and spaces, invalid bear names like and will be ignored.

Also note that in the bear names delimited by commas and spaces, you may specify glob wildcards that match several bears:

# Start ignoring Line*, Py*
unwrappable_string_2 = unwrappable_string + "yeah it goes even further..."
another_unwrappable_string = unwrappable_string + unwrappable_string_2
# Stop ignoring

In the above example all bears matching the glob Line* and Py* will be ignored. You may also specify more complex globs here such as # Start ignoring (Line*|P[yx]*) which will ignore all bears’ names which start with Line, Py, and Px.

# Ignore LineLengthBear and SpaceConsistencyBear
    variable = "Why the heck are spaces used instead of tabs..." + "so_long"

If you put an all instead of the bear names directly after the ignore/ignoring keyword, the results of all bears affecting those lines will be ignored.

If you’ve used another linter in the past, you don’t have to change your pre-existing code with the noqa keywords to ignore as the examples below work as well. If no bears are specified, noqa will be applicable to work for all bears.

# noqa
long_line = "This is a long line ... "

If you wish to specify which bear to use with noqa, as is done with ignore, you would have to proceed as follows:

# noqa LineLengthBear
long_line = "This is a long line ... "

Enabling/Disabling Sections

Now that we have sections we need some way to control, which sections are executed. coala provides two ways to do that:

Manual Enabling/Disabling

If you add the line TODOS.enabled=False to some arbitrary place to your .coafile or just enabled=False into the TODOS section, coala will not show the TODOs on every run.

Especially for those bears yielding informational messages which you might want to see from time to time this is a good way to silence them.

Specifying Targets

If you provide positional arguments, like coala Makefiles, coala will execute exclusively those sections that are specified. This will not get stored in your .coafile and will take precedence over all enabled settings. You can specify several targets separated by a space.

What was that TODO again?

Continuing the Journey

If you want to know about more options, take a look at our coala settings documentation or with coala -h. If you liked or disliked this tutorial, feel free to drop us a note at our bug tracker or mailing list.

If you need more flexibility, know that coala is extensible in many ways due to its modular design:

  • If you want to write your own bears, take a look at our tutorial.
  • If you want to add custom actions for results, take a look at the code in coalib/results/results_actions.
  • If you want to have some custom outputs (e.g. HTML pages, a GUI or voice interaction) take a look at modules lying in coalib/output.

Happy coding!