# Sub The module is a filter that modifies a response by replacing one specified string with another. When [building from the source code](https://en.angie.software//angie/docs/installation/sourcebuild.md#sourcebuild), this module isn't built by default; it should be enabled with the `‑‑with‑http_sub_module` [build option](https://en.angie.software//angie/docs/installation/sourcebuild.md#configure). In packages and images from [our repos](https://en.angie.software//angie/docs/installation/index.md#install-packages), the module is included in the build. ## Configuration Example ```nginx location / { sub_filter ' ## Directives ### sub_filter | [Syntax](https://en.angie.software//angie/docs/configuration/configfile.md#configfile) | `sub_filter` string replacement; | |------------------------------------------------------------------------------------------|------------------------------------| | Default | — | | [Context](https://en.angie.software//angie/docs/configuration/configfile.md#configfile) | http, server, location | Sets a string to replace and a replacement string. The string to replace is matched ignoring the case. The string to replace and replacement string can contain variables. Several `sub_filter` directives can be specified on the same configuration level. These directives are inherited from the previous configuration level if and only if there are no `sub_filter` directives defined on the current level. ### sub_filter_last_modified | [Syntax](https://en.angie.software//angie/docs/configuration/configfile.md#configfile) | `sub_filter_last_modified` `on` | `off`; | |------------------------------------------------------------------------------------------|--------------------------------------------| | Default | `sub_filter_last_modified off;` | | [Context](https://en.angie.software//angie/docs/configuration/configfile.md#configfile) | http, server, location | Allows preserving the `Last-Modified` header field from the original response during replacement to facilitate response caching. By default, the header field is removed as contents of the response are modified during processing. ### sub_filter_once | [Syntax](https://en.angie.software//angie/docs/configuration/configfile.md#configfile) | `sub_filter_once` `on` | `off`; | |------------------------------------------------------------------------------------------|-----------------------------------| | Default | `sub_filter_once on;` | | [Context](https://en.angie.software//angie/docs/configuration/configfile.md#configfile) | http, server, location | Indicates whether to look for each string to replace once or repeatedly. ### sub_filter_types | [Syntax](https://en.angie.software//angie/docs/configuration/configfile.md#configfile) | `sub_filter_types` mime-type ...; | |------------------------------------------------------------------------------------------|-------------------------------------| | Default | `sub_filter_types text/html;` | | [Context](https://en.angie.software//angie/docs/configuration/configfile.md#configfile) | http, server, location | Enables string replacement in responses with the specified MIME types in addition to `text/html`. The special value "\*" matches any MIME type.