The file command is a standard program of Unix and Unix-like operating systems for recognizing the type of data contained in a computer file. 展开

The Single UNIX Specification (SUS) specifies that a series of tests are performed on the file specified on the command line:
1. if the file … 展开

Note that -s is a non-standard option available only on the Ian Darwin branch, which tells file to read device files and try to identify their contents rather than merely identifying them as device files. Normally file does not try to read device files since reading such a file can … 展开

• file: determine file type – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group
Manual pages
• file(1) – Linux User Manual – User Commands 展开

The original version of file originated in Unix Research Version 4 in 1973. System V brought a major update with several important changes, most notably moving the file type information … 展开

The SUS mandates the following options:
• -M file, specify a file specially formatted containing position-sensitive tests; default position-sensitive tests and context-sensitive tests will not be performed.
• -m file, as for -M, but default tests will be performed after the tests … 展开

As of version 4.00 of the Ian Darwin/Christos Zoulas version of file, the functionality of file is incorporated into a libmagic library that is accessible via C (and C-compatible) … 展开