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Learn Linux, 101: Text streams and filters

Aug 31, 2009, 23:03 (0 Talkback[s])
(Other stories by Ian Shields)

[ Thanks to An Anonymous Reader for this link. ]

"Text filtering
Text filtering is the process of taking an input stream of text and performing some conversion on the text before sending it to an output stream. Although either the input or the output can come from a file, in the Linux and UNIX® environments, filtering is most often done by constructing a pipeline of commands where the output from one command is piped or redirected to be used as input to the next. Pipes and redirection are covered more fully in the article on streams, pipes, and redirects (which you can find in the series roadmap), but for now, let's look at pipes and basic output redirection using the | and > operators.

A stream is nothing more than a sequence of bytes that can be read or written using library functions that hide the details of an underlying device from the application. The same program can read from, or write to a terminal, file, or network socket in a device-independent way using streams. Modern programming environments and shells use three standard I/O streams:

"stdin is the standard input stream, which provides input to commands.

"stdout is the standard output stream, which displays output from commands.

"stderr is the standard error stream, which displays error output from commands."

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