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Regular file

A regular file is one type of file stored in a file system. It is called «regular» primarily to distinguish it from other special types of files.

Most files used directly by a human user are regular files. For example, executable files, text files, and image files are regular files.

When data is read from or written to a regular file, the kernel performs that action according to the rules of the filesystem. For instance, writes may be delayed, journaled, or subject to other special operations.

Linux file types

In the Linux kernel, file types are declared in the header file sys/stat.h. The type name, symbolic name, and bitmask for each Linux file type is listed below.

Type name	Symbolic name	Bitmask
Socket	S_IFSOCK	0140000
Symbolic link	S_IFLNK	0120000
Regular file	S_IFREG	0100000
Block special file	S_IFBLK	0060000
Directory	S_IFDIR	0040000
Character device	S_IFCHR	0020000
FIFO (named pipe)	S_IFIFO	0010000

How can I tell if a file is regular?

In bash, the command «test -f file» returns an exit status of 0 if file is a regular file. It returns 1 if file is of another type or does not exist.

You can also check a file’s type with stat:

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File types In Linux/Unix explained in detail.

“ How many types of files are there in Linux/Unix and what are they? ” This is a common question to every person who starts to learn Linux. O.K, why is it that much important to know file types?

Answer: This is because Linux considers every thing as a file. When ever you start working on Linux/Unix box you have to deal with different file types(linux/unix) to effectively manage them

How many types of file are there in Linux/Unix?

By default Unix have only 3 types of files. They are..

Special files(This category is having 5 sub types in it.)

So in practical we have total 7 types(1+1+5) of files in Linux/Unix. And in Solaris we have 8 types. And you can see the file type indication at leftmost part of “ls -l” command.

Here are those files type.

1. Block file(b)
2. Character d evice file(c)
3. Named pipe file or just a pipe file(p)
4. Symbolic link file(l)
5. Socket file(s)

For your information there is one more file type called door file(D) which is present in Sun Solaris as mention earlier. A door is a special file for inter-process communication between a client and server (so total 8 types in Unix machines). We will learn about different types of files as below sequence for every file type.

Regular file type Explained in Linux

These are the files which are indicated with “-” in ls -l command output at the starting of the line. And these files are.

How to create regular files in Linux/Unix?
Ans: Use touch/vi command and redirection operators etc.

How can we list regular files?

Example listing of regular files :

Directory file type explained in Linux/Unix

These type of files contains regular files/folders/special files stored on a physical device. And this type of files will be in blue in color with link greater than or equal 2.

Example listing of directories.

How to create them?
Ans : Use mkdir command

Block file type in Linux

These files are hardware files most of them are present in /dev.

How to create them?
Ans : Use fdisk command or create virtual partition.

How can we list them in my present working directory?

Example listing of Block files(for you to see these file, they are located in /dev).

Character device files in Linux

Provides a serial stream of input or output.Your terminals are classic example for this type of files.

How can we list character files in my present working directory?

Example listing of character files(located in /dev)

Pipe files in Linux/Unix

The other name of pipe is a “named” pipe, which is sometimes called a FIFO. FIFO stands for “First In, First Out” and refers to the property that the order of bytes going in is the same coming out. The “name” of a named pipe is actually a file name within the file system.

How to create them?
Ans: Use mkfifo command.

How can we list character files in my present working directory?

Example listing of pipe files

symbolic link files in Linux

These are linked files to other files. They are either Directory/Regular File. The inode number for this file and its parent files are same. There are two types of link files available in Linux/Unix ie soft and hard link.

How to create them?
Ans : use ln command

How can we list linked files in my present working directory ?

Socket files in Linux

A socket file is used to pass information between applications for communication purpose

How to create them?
Ans : You can create a socket file using socket() system call available under

Example in C programming

You can refer to this socket file using the sockfd. This is same as the file descriptor, and you can use read(), write() system calls to read and write from the socket.

How can we list Socket files in my present working directory?

Example listing of socket files.

srw-rw-rw- 1 root root 0 2010-02-15 09:35 /dev/log

A tip for you guys. How to find your desired type of file ?

Ans : Use find command with -type option. For example if you want to find socket file, just use below command. find / -type s If you want to find linked file then how? Find / -type l

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Файлы в Linux

Типы файлов в Linux

В Linux всё является файлами и tty терминалы не исключение.

Или аналогичную команду

crw—w—-. 1 andrei tty 136, 1 Nov 19 12:43 /dev/pts/1

Первый символ — это тип файла.

Доступно семь типов файлов: обычные, директории, символьные, блоки, сокеты, именованые каналы, символьные ссылки

— : regular file
d : directory
c : character device file
b : block device file
s : local socket file
p : named pipe
l : symbolic link

Тип c означает character. То есть этот файл может принимать и показывать символы

drwxr-xr-x. 118 root root 8192 Nov 19 11:02 /etc

Видно, что тип файла d. То есть directory

Для просмотра дисков/блоков выполните

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 8G 0 disk ├─sda1 8:1 0 1G 0 part /boot └─sda2 8:2 0 7G 0 part ├─centos-root 253:0 0 6.2G 0 lvm / └─centos-swap 253:1 0 820M 0 lvm [SWAP] sr0 11:0 1 57.7M 0 rom /run/media/andrei/VBox_GAs_6.1.10

brw-rw—-. 1 root disk 8, 0 Nov 19 11:02 /dev/sda brw-rw—-. 1 root disk 8, 1 Nov 19 11:02 /dev/sda1 brw-rw—-. 1 root disk 8, 2 Nov 19 11:02 /dev/sda2

Можно убедитсья, что тип файлов b. То есть block

? означает что должен быть один любой символ.

brw-rw—-. 1 root disk 8, 1 Nov 19 11:02 /dev/sda1 brw-rw—-. 1 root disk 8, 2 Nov 19 11:02 /dev/sda2

[12] означает что должен быть либо символ 1 либо символ 2

brw-rw—-. 1 root disk 8, 1 Nov 19 11:02 /dev/sda1 brw-rw—-. 1 root disk 8, 2 Nov 19 11:02 /dev/sda2

Когда вы хотите узнать версию системы вы можете выполнить

ls -l /etc/system-release

lrwxrwxrwx. 1 root root 14 Nov 17 13:44 /etc/system-release -> centos-release

Тип файла l означает link то есть это не настоящий файл, а ссылка

ls -l /etc/system-release /etc/centos-release /etc/redhat-release

-rw-r—r—. 1 root root 37 Oct 23 17:53 /etc/centos-release lrwxrwxrwx. 1 root root 14 Nov 17 13:44 /etc/redhat-release -> centos-release lrwxrwxrwx. 1 root root 14 Nov 17 13:44 /etc/system-release -> centos-release

/etc/centos-release — это настоящий (regular) файл а остальные — ссылки на него.

Если бы вы пользовались redhat то настоящим был бы redhat-release

Ещё один способ получить информацию о версии — выполнить lsb_release -d где -d означает description

Description: CentOS Linux release 7.9.2009 (Core)

Узнать расположение файла

Узнать где находится файл lsb_release можно командой which lsb_release. Чтобы сразу получить дополнительную информацию выполните

ls -lF $(which lsb_release)

-rwxr-xr-x. 1 root root 15929 Mar 27 2015 /usr/bin/lsb_release*

Опция -F означает показать тип файлов. Поэтому нам удалось увидеть * после lsb_release. * означает, что файл исполняемый.

Чтобы узнать откуда взялся файл можно воспользоваться командой rpm с опциями q (query) и f (file)

rpm -qf $(which lsb_release)

Чтобы скопировать файл в интерактивном режиме воспользуйтесь командой cp с опцией i (interactive)

interactive означает, что если файл с таким имененм существует, вас спросят прежде чем затирать его

cp -i /etc/hosts .
cp -i /etc/hosts .

cp: overwrite ‘./hosts’?

Чтобы создать директорию сразу же с поддиректорией внутри воспользуйтесь командлой mkdir с опцией p (parent)

mkdir -p sites/heiheiru
ls -l sites

total 0
drwxrwxr-x. 2 andrei andrei 6 Nov 19 13:40 heiheiru

Создать сразу несколько файлов

Чтобы создать одновременно несколько файлов с именами идущими по порядку выполните touch с <>

touch files/file <1..5>
ls -l files

-rw-rw-r—. 1 andrei andrei 0 Nov 19 13:46 file1 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:46 file2 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:46 file3 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:46 file4 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:46 file5

Чтобы скопировать директорию files в директорию sites со всем содержимым выполните

cp -R files sites
ls -l sites/files/

total 0 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:49 file1 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:49 file2 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:49 file3 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:49 file4 -rw-rw-r—. 1 andrei andrei 0 Nov 19 13:49 file5

Директория files была скопирована в директорию sites, то есть теперь у sites есть поддиректория files.

Если у вас установлен модуль tree вы можете наглядно изучить вложенность. Если нет — выполните сперва sudo yum install tree

sites └── files ├── file1 ├── file2 ├── file3 ├── file4 └── file5 1 directory, 5 files

Создать ссылку можно командой ln, символьную ссылку ln -s

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file(1) — Linux man page

file — determine file type

Synopsis

Description

This manual page documents version 5.04 of the file command.

file tests each argument in an attempt to classify it. There are three sets of tests, performed in this order: filesystem tests, magic tests, and language tests. The first test that succeeds causes the file type to be printed.

The type printed will usually contain one of the words text (the file contains only printing characters and a few common control characters and is probably safe to read on an ASCII terminal), executable (the file contains the result of compiling a program in a form understandable to some UNIX kernel or another), or data meaning anything else (data is usually ‘binary’ or non-printable). Exceptions are well-known file formats (core files, tar archives) that are known to contain binary data. When modifying magic files or the program itself, make sure to preserve these keywords. Users depend on knowing that all the readable files in a directory have the word ‘text’ printed. Don’t do as Berkeley did and change ‘shell commands text’ to ‘shell script’.

The filesystem tests are based on examining the return from a stat(2) system call. The program checks to see if the file is empty, or if it’s some sort of special file. Any known file types appropriate to the system you are running on (sockets, symbolic links, or named pipes (FIFOs) on those systems that implement them) are intuited if they are defined in the system header file

The magic tests are used to check for files with data in particular fixed formats. The canonical example of this is a binary executable (compiled program) a.out file, whose format is defined in #include
and possibly #include
in the standard include directory. These files have a ‘magic number’ stored in a particular place near the beginning of the file that tells the UNIX operating system that the file is a binary executable, and which of several types thereof. The concept of a ‘magic’ has been applied by extension to data files. Any file with some invariant identifier at a small fixed offset into the file can usually be described in this way. The information identifying these files is read from the compiled magic file /usr/share/misc/magic.mgc, or the files in the directory /usr/share/misc/magic if the compiled file does not exist. In addition, if $HOME/.magic.mgc or $HOME/.magic exists, it will be used in preference to the system magic files. If /etc/magic exists, it will be used together with other magic files.

If a file does not match any of the entries in the magic file, it is examined to see if it seems to be a text file. ASCII, ISO-8859-x, non-ISO 8-bit extended-ASCII character sets (such as those used on Macintosh and IBM PC systems), UTF-8-encoded Unicode, UTF-16-encoded Unicode, and EBCDIC character sets can be distinguished by the different ranges and sequences of bytes that constitute printable text in each set. If a file passes any of these tests, its character set is reported. ASCII, ISO-8859-x, UTF-8, and extended-ASCII files are identified as ‘text’ because they will be mostly readable on nearly any terminal; UTF-16 and EBCDIC are only ‘character data’ because, while they contain text, it is text that will require translation before it can be read. In addition, file will attempt to determine other characteristics of text-type files. If the lines of a file are terminated by CR, CRLF, or NEL, instead of the Unix-standard LF, this will be reported. Files that contain embedded escape sequences or overstriking will also be identified.

Once file has determined the character set used in a text-type file, it will attempt to determine in what language the file is written. The language tests look for particular strings (cf. #include
) that can appear anywhere in the first few blocks of a file. For example, the keyword .br indicates that the file is most likely a troff(1) input file, just as the keyword struct indicates a C program. These tests are less reliable than the previous two groups, so they are performed last. The language test routines also test for some miscellany (such as tar(1) archives).

Any file that cannot be identified as having been written in any of the character sets listed above is simply said to be ‘data’.

Options

-C, —compile
Write a magic.mgc output file that contains a pre-parsed version of the magic file or directory.

-c, —checking-printout
Cause a checking printout of the parsed form of the magic file. This is usually used in conjunction with the -m flag to debug a new magic file before installing it.

-e, —exclude testname
Exclude the test named in testname from the list of tests made to determine the file type. Valid test names are:

apptype
EMX application type (only on EMX).

text’ Various types of text files (this test will try to guess the text encoding, irrespective of the setting of the ‘encoding’ option).

encoding
Different text encodings for soft magic tests.

tokens’ Looks for known tokens inside text files.

cdf’ Prints details of Compound Document Files.

compress
Checks for, and looks inside, compressed files.

elf’ Prints ELF file details.

soft’ Consults magic files.

tar’ Examines tar files.

-F, —separator separator
Use the specified string as the separator between the filename and the file result returned. Defaults to ‘:’.

-f, —files-from namefile
Read the names of the files to be examined from namefile (one per line) before the argument list. Either namefile or at least one filename argument must be present; to test the standard input, use ‘-‘ as a filename argument.

-h, —no-dereference
option causes symlinks not to be followed (on systems that support symbolic links). This is the default if the environment variable POSIXLY_CORRECT is not defined.

-i, —mime
Causes the file command to output mime type strings rather than the more traditional human readable ones. Thus it may say ‘text/plain; charset=us-ascii’ rather than ‘ASCII text’. In order for this option to work, file changes the way it handles files recognized by the command itself (such as many of the text file types, directories etc), and makes use of an alternative ‘magic’ file. (See the FILES section, below).

—mime-type, —mime-encoding
Like -i, but print only the specified element(s).

-k, —keep-going
Don’t stop at the first match, keep going. Subsequent matches will be have the string ‘\012- ‘ prepended. (If you want a newline, see the ‘-r’ option.)

-L, —dereference
option causes symlinks to be followed, as the like-named option in ls(1) (on systems that support symbolic links). This is the default if the environment variable POSIXLY_CORRECT is defined.

-m, —magic-file magicfiles
Specify an alternate list of files and directories containing magic. This can be a single item, or a colon-separated list. If a compiled magic file is found alongside a file or directory, it will be used instead.

-N, —no-pad
Don’t pad filenames so that they align in the output.

-n, —no-buffer
Force stdout to be flushed after checking each file. This is only useful if checking a list of files. It is intended to be used by programs that want filetype output from a pipe.

-p, —preserve-date
On systems that support utime(2) or utimes(2), attempt to preserve the access time of files analyzed, to pretend that file never read them.

-r, —raw
Don’t translate unprintable characters to \ooo. Normally file translates unprintable characters to their octal representation.

-s, —special-files
Normally, file only attempts to read and determine the type of argument files which stat(2) reports are ordinary files. This prevents problems, because reading special files may have peculiar consequences. Specifying the -s option causes file to also read argument files which are block or character special files. This is useful for determining the filesystem types of the data in raw disk partitions, which are block special files. This option also causes file to disregard the file size as reported by stat(2) since on some systems it reports a zero size for raw disk partitions.

-v, —version
Print the version of the program and exit.

-z, —uncompress
Try to look inside compressed files.

-0, —print0
Output a null character ‘\0’ after the end of the filename. Nice to cut(1) the output. This does not affect the separator which is still printed.

—help
Print a help message and exit.

Files

Environment

The environment variable MAGIC can be used to set the default magic file name. If that variable is set, then file will not attempt to open $HOME/.magic. file adds ‘.mgc’ to the value of this variable as appropriate. The environment variable POSIXLY_CORRECT controls (on systems that support symbolic links), whether file will attempt to follow symlinks or not. If set, then file follows symlink, otherwise it does not. This is also controlled by the -L and -h options.

See Also

Standards Conformance

This program is believed to exceed the System V Interface Definition of FILE(CMD), as near as one can determine from the vague language contained therein. Its behavior is mostly compatible with the System V program of the same name. This version knows more magic, however, so it will produce different (albeit more accurate) output in many cases.

The one significant difference between this version and System V is that this version treats any white space as a delimiter, so that spaces in pattern strings must be escaped. For example, in an existing magic file would have to be changed to In addition, in this version, if a pattern string contains a backslash, it must be escaped. For example in an existing magic file would have to be changed to SunOS releases 3.2 and later from Sun Microsystems include a file command derived from the System V one, but with some extensions. My version differs from Sun’s only in minor ways. It includes the extension of the ‘&’ operator, used as, for example,

Magic Directory

The magic file entries have been collected from various sources, mainly USENET, and contributed by various authors. Christos Zoulas (address below) will collect additional or corrected magic file entries. A consolidation of magic file entries will be distributed periodically.

The order of entries in the magic file is significant. Depending on what system you are using, the order that they are put together may be incorrect. If your old file command uses a magic file, keep the old magic file around for comparison purposes (rename it to /usr/share/misc/magic.orig ).

Examples

/dev/wd0a: block special (0/0)
/dev/hda: block special (3/0)

$ file -s /dev/wd0
/dev/wd0b: data
/dev/wd0d: x86 boot sector

$ file -s /dev/hda<,1,2,3,4,5,6,7,8,9,10>
/dev/hda: x86 boot sector
/dev/hda1: Linux/i386 ext2 filesystem
/dev/hda2: x86 boot sector
/dev/hda3: x86 boot sector, extended partition table
/dev/hda4: Linux/i386 ext2 filesystem
/dev/hda5: Linux/i386 swap file
/dev/hda6: Linux/i386 swap file
/dev/hda7: Linux/i386 swap file
/dev/hda8: Linux/i386 swap file
/dev/hda9: empty
/dev/hda10: empty

$ file -i file.c file /dev/
file.c: text/x-c
file: application/x-executable
/dev/hda: application/x-not-regular-file
/dev/wd0a: application/x-not-regular-file

History

There has been a file command in every UNIX since at least Research Version 4 (man page dated November, 1973). The System V version introduced one significant major change: the external list of magic types. This slowed the program down slightly but made it a lot more flexible.

This program, based on the System V version, was written by Ian Darwin without looking at anybody else’s source code.

John Gilmore revised the code extensively, making it better than the first version. Geoff Collyer found several inadequacies and provided some magic file entries. Contributions by the ‘&’ operator by Rob McMahon, cudcv@warwick.ac.uk, 1989.

Guy Harris, guy@netapp.com, made many changes from 1993 to the present.

Primary development and maintenance from 1990 to the present by Christos Zoulas (christos@astron.com).

Altered by Chris Lowth, chris@lowth.com, 2000: Handle the -i option to output mime type strings, using an alternative magic file and internal logic.

Altered by Eric Fischer (enf@pobox.com), July, 2000, to identify character codes and attempt to identify the languages of non-ASCII files.

Altered by Reuben Thomas (rrt@sc3d.org), 2007 to 2008, to improve MIME support and merge MIME and non-MIME magic, support directories as well as files of magic, apply many bug fixes and improve the build system.

The list of contributors to the ‘magic’ directory (magic files) is too long to include here. You know who you are; thank you. Many contributors are listed in the source files.

Legal Notice

Copyright В© Ian F. Darwin, Toronto, Canada, 1986-1999. Covered by the standard Berkeley Software Distribution copyright; see the file LEGAL.NOTICE in the source distribution.

The files tar.h and is_tar.c were written by John Gilmore from his public-domain tar(1) program, and are not covered by the above license.

There must be a better way to automate the construction of the Magic file from all the glop in Magdir. What is it?

file uses several algorithms that favor speed over accuracy, thus it can be misled about the contents of text files.

The support for text files (primarily for programming languages) is simplistic, inefficient and requires recompilation to update.

The list of keywords in ascmagic probably belongs in the Magic file. This could be done by using some keyword like ‘*’ for the offset value.

Complain about conflicts in the magic file entries. Make a rule that the magic entries sort based on file offset rather than position within the magic file?

The program should provide a way to give an estimate of ‘how good’ a guess is. We end up removing guesses (e.g. ‘Fromas first 5 chars of file) because’ they are not as good as other guesses (e.g. ‘Newsgroups:’ versus ‘Return-Path:’ ). Still, if the others don’t pan out, it should be possible to use the first guess.

This manual page, and particularly this section, is too long.

Return Code

file returns 0 on success, and non-zero on error.

If the file named by the file operand does not exist, cannot be read, or the type of the file named by the file operand cannot be determined, this is not be considered an error that affects the exit status.

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