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Cute decorative scissors, cutting through your code.

The nginx-confgen(1) Man Page


nginx-confgen - A preprocessor and macro system for nginx(-like) configuration files.


nginx-confgen -i input.conf -o output.conf


nginx-confgen can be used to do pre-processing for nginx configuration files (and other configuration files with a similar syntax). It has support for "compile-time" macro expansion and variable interpolation, which should make it less tedious to maintain large and complex configurations.

nginx-confgen works by parsing the input into a syntax tree, modifying this tree, and then formatting the tree to generate the output. It is completely oblivious to nginx contexts and directives, so it is possible to do nonsensical transformations and generate incorrect configuration files. Comments in the input file will not be present in the output. See also the "BUGS & WARTS" below.

WARNING: Do NOT use nginx-confgen with untrusted input, the pre_exec directive allows, by design, arbitrary code execution.


The following command-line options are supported:


Show help text.

-V, --version

Show program version.


Use the given file name as input file. If this option is not given or set to -, then the file will be read from standard input.


Write the output to the given file. If this option is not given or set to -, then the file will be written to standard output.


Set the search path for pre_include directives. This option can be given multiple times to search several directories in order. If this option is not given, then include files are resolved relative to the directory that nginx-confgen is run from (i.e. -I .).


nginx-confgen recognizes and interprets the following directives:


Similar to the include directive in nginx, except that the file is included during preprocessing. The included file may contain any preprocessing directives supported by nginx-confgen. Variables and macros defined in the included file will be available in the parent file.

Relative paths are searched for in the directories given with the -I flag.


Similar to the set directive in nginx, except that variables defined with pre_set are resolved during preprocessing. Note that variables defined with pre_set are only available in the same scope as they are defined, for example:

pre_set $var outer;
location / {
  pre_set $var inner;
  # $var is now "inner" within this location block.
# $var is "outer" again after the location block.

(This may change in the future)


Run a shell command, and store the output in a variable. For example, nginx will not use your system's DNS resolution methods to resolve domain names. Instead you need to manually set a resolver address. With the following hack you can fetch the nameserver from /etc/resolv.conf and use that as the resolver:

pre_exec $nameserver "grep nameserver /etc/resolv.conf \\
                      | head -n 1 | sed 's/^nameserver //'";
resolver $nameserver;

(The \\ is necessary, otherwise your shell will consider the newline as a new command).


Similar to the if directive in nginx, except that this is evaluated during preprocessing. Also unlike if, parenthesis around the arguments are not supported. Some examples:

pre_if -f $certdir/ocsp.der {
  ssl_stapling on;
  ssl_stapling_file $certdir/ocsp.der;
pre_if !-f $certdir/ocsp.der {
  ssl_stapling off;

# You can have different configuration depending on the name of
# the system on which nginx-confgen runs. Like... yeah.
pre_exec $hostname 'hostname';
pre_if $hostname ~* ^proxy_for_(.+) {
  proxy_pass http://$1/;


This directive, when interpreted, will generate a warning to the standard error of nginx-confgen. Can be used to signal that a special configuration is being used:

pre_if -e /etc/offline-mode {
  pre_warn "Putting website in offline mode!";

Or to warn about certain directives:

pre_macro proxy_cache $var {
  pre_warn "Using proxy_cache with $var violates company policy!";

  # But we can output it anyway.
  proxy_cache $var;


Define a macro, which is a configuration block that you can later refer to. The general syntax is as follows:

macro macro_name $var1 $var2 @remaining_vars &block_var {
  # contents

The optional @remaining_vars argument will capture any number of variables, and can be passed to another directive inside the macro contents. The optional &block_var allows the macro to be invoked with a block argument, which will expand to any number of directives. Some examples:

macro le {
  location /.well-known/acme-challenge {
    alias /etc/letsencrypt/challenge;
# Usage:

macro redir $path $to {
  location $path {
    return 301 $to;
# Usage:
redir / http://blicky.net/;

macro vhost $primary_name @aliases &block {
  server {
    listen [::]:443 ssl;
    server_name $primary_name @aliases;
    ssl_certificate $crtdir/$primary_name/fullchain.pem;
    ssl_certificate_key $crtdir/$primary_name/privkey.pem;
# Usage:
vhost example.com {
  root /var/www/example.com;
vhost example.org alias.example.org {
  root /var/www/example.org;

Note that these are hygienic macros, so variable capture is predictable (but not necessarily the most useful):

pre_var $dest /a;
macro redir {
  # This will be /a, regardless of the context in which this macro is called.
  return 301 $dest;
# $dest is still '/a' inside the macro after this new variable definition.
pre_var $dest /b;

Similarly, macro arguments will not be available inside &block expansion or nested macro expansion.


nginx-confgen is a quickly written hack to solve a particular use case, it is quite likely to have some weird behavior and bugs.

Comments and whitespace in the input files are thrown away and ignored. The generated output is completely reformatted.

The nginx configuration syntax is not as regular as I had hoped. It's possible for nginx modules to extend the syntax somewhat. A good example is the types directive in ngx_http_core_module. While nginx-confgen should be able to handle the types directive just fine, other extensions may cause syntax errors or will not survive a round-trip through nginx-confgen. This applies to all *_by_lua_block directives in the ngx_http_lua_module. The _by_lua directives that accept a string should work just fine.

The error messages given by nginx-confgen aren't always helpful.


nginx-confgen is written by Yoran Heling <projects@yorhel.nl>

Web: https://dev.yorhel.nl/nginx-confgen