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This is a simple Hello World example. It explains basics of making applications as well as tracing and debugging them.

In a nutshell:  command line; web browser; Nginx; Unix sockets; 2 source files, 7 lines of code.
Hello World output:


Install Vely - you can use standard packaging tools such as apt, dnf, pacman or zypper.

Because it is used in this example, you will need to install Nginx as a web server.

After installing Vely, turn on syntax highlighting in vim if you're using it:

The source code is a part of Vely installation. It is a good idea to create a separate source code directory for each application (and you can name it whatever you like). In this case, unpacking the source code will do that for you:

The very first step is to create an application. The application will be named "hello_world", but you can name it anything (if you do that, change it everywhere). It's simple to do with vf:

This will create a new application home (which is "/var/lib/vv/hello_world") and do the application setup for you. Mostly that means create various subdirectories in the home folder, and assign them privileges. In this case only current user (or the result of "whoami" Linux command) will own those directories with 0700 privileges; it means a secure setup.
Use vv utility to make the application:

To start the application server for your web application use vf FastCGI process manager. The application server will use a Unix socket to communicate with the web server (i.e. a reverse-proxy):

This will start 3 daemon processes to serve the incoming requests. You can also start an adaptive server that will increase the number of processes to serve more requests, and gradually reduce the number of processes when they're not needed:

See vf for more options to help you achieve best performance.

If you want to stop your application server:

This shows how to connect your application listening on a Unix socket (started with vf) to Nginx web server.

- Step 1:
You will need to edit the Nginx configuration file. For Ubuntu and similar:

while on Fedora and other systems it might be at:


Add the following in the "server {}" section ("/hello_world" is the application path (see request_URL) and "hello_world" is your application name):

- Step 2:
Finally, restart Nginx:

Note: you must not have any other URL resource that starts with "/hello_world" (such as for example "/hello_world.html" or "/hello_world_something" etc.) as the web server will attempt to pass them as a reverse proxy request, and they will likely not work. If you need to, you can change the application path to be different from "/hello_world", see request_URL.
Use the following URL(s) to access your application server from a client like browser (see request_URL). Use actual IP or web address instead of 127.0.0.1 if different.

Note: if your server is on the Internet and it has a firewall, you may need to allow HTTP traffic - see ufw, firewall-cmd etc.
To access your application server from command line (instead through web browser/web server), use "cgi-fcgi" to see the application response:

Note: to suppress output of HTTP headers, add this before running "cgi-fcgi":

If you need to, you can also run your application as a CGI program.
Execute the following to run your application from command line (as a command-line utility):

Note: to suppress output of HTTP headers, add this before running /var/lib/vv/bld/hello_world/hello_world program:

Note: if running your program as a command-line utility is all you want, you don't need to run an application server.
You are now done with the example! What follows are the source files in this project so you can examine how it works:
Hello World example outputs HTTP header and a simple message back to the browser.

The file name ("hello.vely") must match the function name implemented in it, so the function's signature is "void hello()". Call it with a URL like:

Note "/hello_world" path segment - that's the application path and by default the same as application name (see how_vely_works and request_URL). The following path segment is "/hello", which is the request name, and it must match the function name that implements it.

Note the "@" is used to do the output, it's the output_statement. You'll probably use that one a lot.

In this case there's only one request file. In a real world application, there'd likely be quite a few. Vely will pick up all .vely files and automatically make them into an application. While at it, it will generate a simple request dispatcher that routes an incoming request to the appropriate code; in this case a "hello" request will be routed to your "void hello()" function.

When you change your source code and recompile, vf will automatically pick up that the executable has changed and reload (see vf if you wish to change this behavior), making your web application live instantly. For example, change hello.vely to this:

and then recompile:

Now try again from the browser:

The result:


Generated C code is located at:

It's useful if you'd like to see it or debug your code.

If you are using your Vely application as a command line program, you can debug it simply by using gdb.

Note that in order to see the debugging symbols (such as variable names), you should compile your application with --debug flag:

For FastCGI processes, you'd want to start your application as a single process, generally as few as possible, for example, stop your application first and then start as a single process:

First, find out the PID of your process:

Then you can load gdb with your application and attach to it - assuming the PID is 12345:

To break in your code (in this case in function hello()), do this in gdb:

If you'd like to break in Vely's request dispatcher, i.e. just before any request is handled:

From then on, you can set breakpoints, continue, stop and do anything else to debug your program.

When you debug Vely applications in gdb, each Vely statement is a single execution unit. This is very useful when reporting errors, since they are reported referencing lines in .vely file, in this case hello.vely. Sometimes you'd want to use line numbers of the generated C file, in which case you'd compile with --c-lines flag:

Another way to debug your application is to use tracing (see trace-run). To enable tracing, compile your application with --trace flag:

Trace files are in the trace directory, see how_vely_works. In our case, trace file would be in this directory:

and trace file name for the process you're debugging would be (with timestamp being of the time it's written):

In addition to this, learn more about debugging Vely applications.
Examples ( example_cookies   example_create_table   example_docker   example_file_manager   example_form   example_hash   example_hello_world   example_json   example_multitenant_SaaS   examples   example_sendmail   example_shopping   example_stock   example_utility   example_write_report  )  SEE ALL (documentation)

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