Named pipe


In computing, a named pipe (also known as a FIFO for its behavior) is an extension to the traditional pipe concept on Unix and Unix-like systems, and is one of the methods ofinter-process communication (IPC). The concept is also found in Microsoft Windows, although the semantics differ substantially. A traditional pipe is “unnamed” because it exists anonymously and persists only for as long as the process is running. A named pipe is system-persistent and exists beyond the life of the process and must be deleted once it is no longer being used. Processes generally attach to the named pipes (usually appearing as a file) to perform inter-process communication.



In Unix[edit]

Instead of a conventional, unnamed, shell pipeline, a named pipeline makes use of the filesystem. It is explicitly created using mkfifo() or mknod(), and two separate processes can access the pipe by name — one process can open it as a reader, and the other as a writer.

For example, one can create a pipe and set up gzip to compress things piped to it:

 mkfifo my_pipe
 gzip -9 -c < my_pipe > out.gz &

In a separate process shell, independently, one could send the data to be compressed:

cat file > my_pipe

The named pipe can be deleted just like any file:

rm my_pipe

A named pipe can be used to transfer information from one application to another without the use of an intermediate temporary file. For example, you can pipe the output of gzip into a named pipe like so:

 mkfifo --mode=0666 /tmp/namedPipe
 gzip --stdout -d file.gz > /tmp/namedPipe

Then load the uncompressed data into a MySQL table[1] like so:

 LOAD DATA INFILE '/tmp/namedPipe' INTO TABLE tableName;

Without this named pipe one would need to write out the entire uncompressed version of file.gz before loading it into MySQL. Writing the temporary file is both time consuming and results in more I/O and less free space on the hard drive.

PostgreSQL‘s command line terminal, psql, also supports loading data from named pipes.[2]


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