The file command is a standard program of Unix and Unix-like operating systems for recognizing the type of data contained in a .
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 into an external text file rather than compiling it into the binary itself.
Most major BSD and Linux distributions use a free, open-source reimplementation which was written in 1986–87 by Ian Darwin from scratch. It was expanded by Geoff Collyer in 1989 and since then has had input from many others, including Guy Harris, Chris Lowth and Eric Fischer; from late 1993 onward its maintenance has been organized by Christos Zoulas. The OpenBSD system has its own subset implementation written from scratch, but still uses the Darwin/Zoulas collection of magic file formatted information.
The command has also been ported to the IBM i operating system.
The Single UNIX Specification (SUS) specifies that a series of tests are performed on the file specified on the command line:
if the file cannot be read, or its is undetermined, the file program will indicate that the file was processed but its type was undetermined.
file must be able to determine the types directory, FIFO, socket, block , and character special file
zero-length files are identified as such
an initial part of file is considered and file is to use position-sensitive tests
the entire file is considered and file is to use context-sensitive tests
the file is identified as a data file
file's position-sensitive tests are normally implemented by matching various locations within the file against a textual database of magic numbers (see the Usage section). This differs from other simpler methods such as s and schemes like MIME.
In most implementations, the file command uses a database to drive the probing of the lead bytes. That database is implemented in a file called magic, whose location is usually in /etc/magic, /usr/share/file/magic or a similar location.
Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.
A file format is a standard way that information is encoded for storage in a . It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free. Some file formats are designed for very particular types of data: PNG files, for example, store bitmapped using lossless data compression. Other file formats, however, are designed for storage of several different types of data: the Ogg format can act as a container for different types of multimedia including any combination of audio and video, with or without text (such as subtitles), and metadata.
thumb|Timbres de Macau, figurant 6 «carrés magiques» (2014) En programmation informatique, le terme magic number (en français ) peut désigner : une constante numérique ou un ensemble de caractères utilisé pour désigner un format de fichier ou un protocole ; une constante numérique non nommée ou mal documentée ; un ensemble de valeurs ayant un sens particulier (par exemple, les GUID). Ce type de magic number est apparu dans les premières versions du code source de la version 7 d'Unix.
gzip (acronyme de GNU zip) est un logiciel libre de compression qui a été créé à partir de 1991 pour remplacer le programme compress d'Unix. gzip est basé sur l'algorithme deflate, qui est une combinaison des algorithmes LZ77 et Huffman. 'Deflate' a été développé en réponse à des problèmes de brevet logiciel couvrant LZW et autres algorithmes de compression, limitant ainsi les utilisations possibles de compress et autres programmes d'archivage populaires.
The principles of 3D surface (SEM) reconstruction and its limitations will be explained. 3D volume reconstruction and tomography methods by electron microscopy (SEM/FIB and TEM) will be explained and
Explore la diffusion totale et l'analyse PDF dans la science des matériaux, couvrant la synthèse in situ, les techniques d'analyse de données et les applications dans les systèmes hôte-invité.