SuperBOL Studio OSS: A New Platform for COBOL

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Visual Studio Code extension for COBOL.

Getting started


This extensions assumes that version 3.2 of GnuCOBOL is available on the system running VS Code. Debug features additionally assume that gdb is installed.


You can install SuperBOL Studio OSS either directly from within VS Code, or via a VSIX file.

Installation within VS Code

First, click on the “Extensions” icon in the activity bar on the left-hand side, or press Ctrl+Shift+X. Then, type “superbol” into the search bar to find it, and press its Install button.

You can find further instructions for installing extensions directly within VS Code on this page.

Installation via a VSIX file

First, download a VSIX file from the Marketplace or Open VSX.

To install the extension from its VSIX file, open VS Code and go to the the “Extensions” view. In the sidebar, click on the three dots (⋅⋅⋅) on the top right-hand side (just above search), select Install from VSIX…. Pick the VSIX file you just downloaded to install it.


This extension should work out-of-the-box on Windows systems where GnuCOBOL has been installed using one of the dedicated installers (available ???). This should be the case with standard installations on Linux as well—e.g, if GnuCOBOL is installed in /usr/local or /usr.

If the extension shows errors like “Configuration file … not found”, you may need to set the COB_CONFIG_DIR environment variable to the directory shown by:

cobc -i | grep COB_CONFIG_DIR

You may need to restart VS Code (or your session) so the extension reloads properly.

Editing an existing project

To start using the extension on an existing project, open its folder in VS Code (File > Add Folder to Workspace…). The extension will start automatically whenever the folder contains files with usual COBOL filename extensions (.cob, .cbl, .cpy, .cbx).

Then, open the settings (File > Preferences > Settings, or Ctrl+,), and start typing “superbol…”. You will be presented with a screen that resembles:

SuperBOL settings

From here, you can notably configure:

Syntax diagnostics

Syntax checks performed by SuperBOL Studio currently cover the COBOL85 dialect, and some constructions of more recent dialects supported by GnuCOBOL. Reporting of such diagnostics is currently disabled to avoid misleading developers with false diagnostics about syntax errors.

Go to Definition

When you want to locate the definition of a data item name in your source code, position your cursor on its name, right click, and select Go to Definition (or press F12).

Go to Definition

Peek Definition

To only have a peek at where such a data item defined, you can position the cursor on its name, right click, and select Peek > Peek Definition (or press Ctrl+Shift+F10). You will then be presented with a view of the location of the corresponding definition, including if it lies in a copybook.

Peek Definition in copybook

Go to References

If you want to obtain a list of all references to a named data item, right click and select Go to References (or press Shift+F12). You will then view the location of every reference to this item.

Go to References

At the moment, definitions that belong to some sections of the data division, and some references to data items, are ignored by the extension. They will be covered by the first stable release.

Hover to Show Copybooks

Ever wondered what was behind a COPY directive? Just position your cursor over such a statement, and you will be presented with the contents of the copybook.

Hover over <code>COPY</code>

Hover to Show Source Text Replacements

What’s more? You can see the source text that results from replacement by a REPLACE directive in the same way.

Hover over replacement


In order to debug a COBOL program, you first need to configure a dedicated build task with appropriate debug options. Once this is done, you can launch the compiled program into a debugging session.

Setting up a Build Task for Debugging

After having opened the program to debug, select Terminal > Run Build Task… (Ctrl+Shift+B), Configure Build Task…, and then SuperBOL: build (debug).

Select <code>SuperBOL: build (debug)</code>

Save the task.json as shown. Definitions for this task notably include a for-debug flag, that instructs the compiler to insert debug annotations into generated executable files, as well as extra-args, that can be edited to pass additional arguments to the cobc compiler.

<code>tasks.json</code> for debug

Launching the Compiled Program for Debugging

If needed, you can place a breakpoint on statements (or paragraph titles in the procedure division) by clicking on the red dot that appears when you hover the cursor on the left margin (or with F9). Click on the red dot or press F9 again to remove a breakpoint. Then, to launch the program in debug mode, select Run > Start Debugging (F5). This will run your program until a first breakpoint if reached, or to completion.

Start Debugging

Once stopped on a breakpoint, you can investigate the values of data items from the program using the VARIABLES panel on the left-hand side.

Press F10 to step to the next statement, or F5 again to continue until the next breakpoint, or termination of the program.


Collaborating with other developers

At this point, the settings for your project are stored and managed by VS Code. However, you may plan to collaborate with developers that do not use this editor. For instance, they might want to use our mode for GNU/Emacs, which is located here. Then, we advise you to let SuperBOL Studio store the configuration in a superbol.toml file that will be located at the root of the project.

You can make the extension write your current project configuration into a superbol.toml by entering the command palette (View > Command Palette…, or press Ctrl+Shift+P), and then selecting the command SuperBOL: Write Project Configuration.

SuperBOL: Write Project Configuration

This will save a superbol.toml file at the root of each currently opened project directory. Such a file will not store any user-specific settings, so you can now safely put them under source control. Extensions dedicated to the edition of TOML files, such as tamasfe.even-better-toml, provide the same level of assistance as when you edit .vscode/settings.json.

Editing <code>superbol.toml</code>

Further documentation

You can check further the documentation on using the extension on this page.

Mode for GNU/Emacs

You can find here a mode that allows you to use the SuperBOL LSP server with GNU/Emacs.

Building from sources

If you build from a clone of the git repository, make sure to update submodules:

git submodule update --init --recursive

You first need to install a few external dependencies to build the LSP server and the VSCode extension from sources.

  1. First, you need to install and initialize opam;

  2. Then you need a recent version1 of our build tool drom. The easiest way to have it running is via the following command:

    opam pin add
  3. Install node.js (version >=5.2.0) if it is not already installed.

  4. You can then install all remaining dependencies, and compile the LSP server along with the VS Code extension:

    make build-deps vsix-release


  1. Current version is 0.9.2~dev3 (commit 63a5770). ↩︎