Filter

In software, a filter is a program or component that processes data and passes along only the items that match specified criteria.

In software, a filter is a program or component that processes data and passes along only the items that match specified criteria. Filters are commonly used in pipelines, where the output of one program becomes the input of another, and in content, network, and data-processing systems. The term also has a broader technical meaning in computing as any function that transforms or screens input into output.

Definition

A filter in software is a program or subroutine that receives data, applies rules or transformations, and outputs a resulting stream. The term is used broadly across computing, including data processing and Unix-style command-line tools. A software filter processes a stream of input and produces another stream as output.

Unix and pipeline usage

In Unix and Unix-like operating systems, a filter usually reads from standard input and writes to standard output, making it easy to combine multiple filters in a pipeline. This design allows complex processing to be built from small, focused programs. Filters are often chained together to form pipelines.

Filtering technologies

Government material on content filtering describes a layered model with core technologies and application-layer tools. Examples include blacklists and whitelists, automatic text analysis, access authority control, proxy software, special-purpose browsers, and access-control applications. Core filtering technologies can include URL lists, automatic text analysis, access control, and activity tracing.

Related software areas

The word filter is also used in specialized software for tasks such as data filtering, web filtering, and electronic filter design. In these contexts, the program screens, selects, or transforms data according to defined rules.