1.\" $NetBSD: file.1,v 1.28 2023/08/18 19:00:10 christos Exp $ 2.\" 3.\" $File: file.man,v 1.150 2023/05/21 17:08:34 christos Exp $ 4.Dd May 21, 2023 5.Dt FILE 1 6.Os 7.Sh NAME 8.Nm file 9.Nd determine file type 10.Sh SYNOPSIS 11.Nm 12.Bk -words 13.Op Fl bcdEhiklLNnprsSvzZ0 14.Op Fl Fl apple 15.Op Fl Fl exclude-quiet 16.Op Fl Fl extension 17.Op Fl Fl mime-encoding 18.Op Fl Fl mime-type 19.Op Fl e Ar testname 20.Op Fl F Ar separator 21.Op Fl f Ar namefile 22.Op Fl m Ar magicfiles 23.Op Fl P Ar name=value 24.Ar 25.Ek 26.Nm 27.Fl C 28.Op Fl m Ar magicfiles 29.Nm 30.Op Fl Fl help 31.Sh DESCRIPTION 32This manual page documents version 5.45 of the 33.Nm 34command. 35.Pp 36.Nm 37tests each argument in an attempt to classify it. 38There are three sets of tests, performed in this order: 39filesystem tests, magic tests, and language tests. 40The 41.Em first 42test that succeeds causes the file type to be printed. 43.Pp 44The type printed will usually contain one of the words 45.Em text 46(the file contains only 47printing characters and a few common control 48characters and is probably safe to read on an 49.Dv ASCII 50terminal), 51.Em executable 52(the file contains the result of compiling a program 53in a form understandable to some 54.Tn UNIX 55kernel or another), 56or 57.Em data 58meaning anything else (data is usually 59.Dq binary 60or non-printable). 61Exceptions are well-known file formats (core files, tar archives) 62that are known to contain binary data. 63When modifying magic files or the program itself, make sure to 64.Em preserve these keywords . 65Users depend on knowing that all the readable files in a directory 66have the word 67.Dq text 68printed. 69Don't do as Berkeley did and change 70.Dq shell commands text 71to 72.Dq shell script . 73.Pp 74The filesystem tests are based on examining the return from a 75.Xr stat 2 76system call. 77The program checks to see if the file is empty, 78or if it's some sort of special file. 79Any known file types appropriate to the system you are running on 80(sockets, symbolic links, or named pipes (FIFOs) on those systems that 81implement them) 82are intuited if they are defined in the system header file 83.In sys/stat.h . 84.Pp 85The magic tests are used to check for files with data in 86particular fixed formats. 87The canonical example of this is a binary executable (compiled program) 88.Dv a.out 89file, whose format is defined in 90.In elf.h , 91.In a.out.h 92and possibly 93.In exec.h 94in the standard include directory. 95These files have a 96.Dq magic number 97stored in a particular place 98near the beginning of the file that tells the 99.Tn UNIX 100operating system 101that the file is a binary executable, and which of several types thereof. 102The concept of a 103.Dq magic number 104has been applied by extension to data files. 105Any file with some invariant identifier at a small fixed 106offset into the file can usually be described in this way. 107The information identifying these files is read from the compiled 108magic file 109.Pa /usr/share/misc/magic.mgc , 110or the files in the directory 111.Pa /usr/share/misc/magic 112if the compiled file does not exist. 113In addition, if 114.Pa $HOME/.magic.mgc 115or 116.Pa $HOME/.magic 117exists, it will be used in preference to the system magic files. 118.Pp 119If a file does not match any of the entries in the magic file, 120it is examined to see if it seems to be a text file. 121ASCII, ISO-8859-x, non-ISO 8-bit extended-ASCII character sets 122(such as those used on Macintosh and IBM PC systems), 123UTF-8-encoded Unicode, UTF-16-encoded Unicode, and EBCDIC 124character sets can be distinguished by the different 125ranges and sequences of bytes that constitute printable text 126in each set. 127If a file passes any of these tests, its character set is reported. 128ASCII, ISO-8859-x, UTF-8, and extended-ASCII files are identified 129as 130.Dq text 131because they will be mostly readable on nearly any terminal; 132UTF-16 and EBCDIC are only 133.Dq character data 134because, while 135they contain text, it is text that will require translation 136before it can be read. 137In addition, 138.Nm 139will attempt to determine other characteristics of text-type files. 140If the lines of a file are terminated by CR, CRLF, or NEL, instead 141of the Unix-standard LF, this will be reported. 142Files that contain embedded escape sequences or overstriking 143will also be identified. 144.Pp 145Once 146.Nm 147has determined the character set used in a text-type file, 148it will 149attempt to determine in what language the file is written. 150The language tests look for particular strings (cf. 151.In names.h ) 152that can appear anywhere in the first few blocks of a file. 153For example, the keyword 154.Em .br 155indicates that the file is most likely a 156.Xr troff 1 157input file, just as the keyword 158.Em struct 159indicates a C program. 160These tests are less reliable than the previous 161two groups, so they are performed last. 162The language test routines also test for some miscellany 163(such as 164.Xr tar 1 165archives, JSON files). 166.Pp 167Any file that cannot be identified as having been written 168in any of the character sets listed above is simply said to be 169.Dq data . 170.Sh OPTIONS 171.Bl -tag -width indent 172.It Fl Fl apple 173Causes the 174.Nm 175command to output the file type and creator code as 176used by older MacOS versions. 177The code consists of eight letters, 178the first describing the file type, the latter the creator. 179This option works properly only for file formats that have the 180apple-style output defined. 181.It Fl b , Fl Fl brief 182Do not prepend filenames to output lines (brief mode). 183.It Fl C , Fl Fl compile 184Write a 185.Pa magic.mgc 186output file that contains a pre-parsed version of the magic file or directory. 187.It Fl c , Fl Fl checking-printout 188Cause a checking printout of the parsed form of the magic file. 189This is usually used in conjunction with the 190.Fl m 191option to debug a new magic file before installing it. 192.It Fl d 193Prints internal debugging information to stderr. 194.It Fl E 195On filesystem errors (file not found etc), instead of handling the error 196as regular output as POSIX mandates and keep going, issue an error message 197and exit. 198.It Fl e , Fl Fl exclude Ar testname 199Exclude the test named in 200.Ar testname 201from the list of tests made to determine the file type. 202Valid test names are: 203.Bl -tag -width compress 204.It apptype 205.Dv EMX 206application type (only on EMX). 207.It ascii 208Various types of text files (this test will try to guess the text 209encoding, irrespective of the setting of the 210.Sq encoding 211option). 212.It encoding 213Different text encodings for soft magic tests. 214.It tokens 215Ignored for backwards compatibility. 216.It cdf 217Prints details of Compound Document Files. 218.It compress 219Checks for, and looks inside, compressed files. 220.It csv 221Checks Comma Separated Value files. 222.It elf 223Prints ELF file details, provided soft magic tests are enabled and the 224elf magic is found. 225.It json 226Examines JSON (RFC-7159) files by parsing them for compliance. 227.It soft 228Consults magic files. 229.It simh 230Examines SIMH tape files. 231.It tar 232Examines tar files by verifying the checksum of the 512 byte tar header. 233Excluding this test can provide more detailed content description by using 234the soft magic method. 235.It text 236A synonym for 237.Sq ascii . 238.El 239.It Fl Fl exclude-quiet 240Like 241.Fl Fl exclude 242but ignore tests that 243.Nm 244does not know about. 245This is intended for compatibility with older versions of 246.Nm . 247.It Fl Fl extension 248Print a slash-separated list of valid extensions for the file type found. 249.It Fl F , Fl Fl separator Ar separator 250Use the specified string as the separator between the filename and the 251file result returned. 252Defaults to 253.Sq \&: . 254.It Fl f , Fl Fl files-from Ar namefile 255Read the names of the files to be examined from 256.Ar namefile 257(one per line) 258before the argument list. 259Either 260.Ar namefile 261or at least one filename argument must be present; 262to test the standard input, use 263.Sq - 264as a filename argument. 265Please note that 266.Ar namefile 267is unwrapped and the enclosed filenames are processed when this option is 268encountered and before any further options processing is done. 269This allows one to process multiple lists of files with different command line 270arguments on the same 271.Nm 272invocation. 273Thus if you want to set the delimiter, you need to do it before you specify 274the list of files, like: 275.Dq Fl F Ar @ Fl f Ar namefile , 276instead of: 277.Dq Fl f Ar namefile Fl F Ar @ . 278.It Fl h , Fl Fl no-dereference 279This option causes symlinks not to be followed 280(on systems that support symbolic links). 281This is the default if the environment variable 282.Dv POSIXLY_CORRECT 283is not defined. 284.It Fl i , Fl Fl mime 285Causes the 286.Nm 287command to output mime type strings rather than the more 288traditional human readable ones. 289Thus it may say 290.Sq text/plain; charset=us-ascii 291rather than 292.Dq ASCII text . 293.It Fl Fl mime-type , Fl Fl mime-encoding 294Like 295.Fl i , 296but print only the specified element(s). 297.It Fl k , Fl Fl keep-going 298Don't stop at the first match, keep going. 299Subsequent matches will be 300have the string 301.Sq "\[rs]012\- " 302prepended. 303(If you want a newline, see the 304.Fl r 305option.) 306The magic pattern with the highest strength (see the 307.Fl l 308option) comes first. 309.It Fl l , Fl Fl list 310Shows a list of patterns and their strength sorted descending by 311.Xr magic 5 312strength 313which is used for the matching (see also the 314.Fl k 315option). 316.It Fl L , Fl Fl dereference 317This option causes symlinks to be followed, as the like-named option in 318.Xr ls 1 319(on systems that support symbolic links). 320This is the default if the environment variable 321.Ev POSIXLY_CORRECT 322is defined. 323.It Fl m , Fl Fl magic-file Ar magicfiles 324Specify an alternate list of files and directories containing magic. 325This can be a single item, or a colon-separated list. 326If a compiled magic file is found alongside a file or directory, 327it will be used instead. 328.It Fl N , Fl Fl no-pad 329Don't pad filenames so that they align in the output. 330.It Fl n , Fl Fl no-buffer 331Force stdout to be flushed after checking each file. 332This is only useful if checking a list of files. 333It is intended to be used by programs that want filetype output from a pipe. 334.It Fl p , Fl Fl preserve-date 335On systems that support 336.Xr utime 3 337or 338.Xr utimes 2 , 339attempt to preserve the access time of files analyzed, to pretend that 340.Nm 341never read them. 342.It Fl P , Fl Fl parameter Ar name=value 343Set various parameter limits. 344.Bl -column "elf_phnum" "Default" "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX" 345.It Sy "Name" Ta Sy "Default" Ta Sy "Explanation" 346.It Li bytes Ta 1M Ta max number of bytes to read from file 347.It Li elf_notes Ta 256 Ta max ELF notes processed 348.It Li elf_phnum Ta 2K Ta max ELF program sections processed 349.It Li elf_shnum Ta 32K Ta max ELF sections processed 350.It Li elf_shsize Ta 128MB Ta max ELF section size processed 351.It Li encoding Ta 65K Ta max number of bytes to determine encoding 352.It Li indir Ta 50 Ta recursion limit for indirect magic 353.It Li name Ta 50 Ta use count limit for name/use magic 354.It Li regex Ta 8K Ta length limit for regex searches 355.El 356.It Fl r , Fl Fl raw 357Don't translate unprintable characters to \eooo. 358Normally 359.Nm 360translates unprintable characters to their octal representation. 361.It Fl s , Fl Fl special-files 362Normally, 363.Nm 364only attempts to read and determine the type of argument files which 365.Xr stat 2 366reports are ordinary files. 367This prevents problems, because reading special files may have peculiar 368consequences. 369Specifying the 370.Fl s 371option causes 372.Nm 373to also read argument files which are block or character special files. 374This is useful for determining the filesystem types of the data in raw 375disk partitions, which are block special files. 376This option also causes 377.Nm 378to disregard the file size as reported by 379.Xr stat 2 380since on some systems it reports a zero size for raw disk partitions. 381.It Fl S , Fl Fl no-sandbox 382On systems where libseccomp 383.Pa ( https://github.com/seccomp/libseccomp ) 384is available, the 385.Fl S 386option disables sandboxing which is enabled by default. 387This option is needed for 388.Nm 389to execute external decompressing programs, 390i.e. when the 391.Fl z 392option is specified and the built-in decompressors are not available. 393On systems where sandboxing is not available, this option has no effect. 394.It Fl v , Fl Fl version 395Print the version of the program and exit. 396.It Fl z , Fl Fl uncompress 397Try to look inside compressed files. 398.It Fl Z , Fl Fl uncompress-noreport 399Try to look inside compressed files, but report information about the contents 400only not the compression. 401.It Fl 0 , Fl Fl print0 402Output a null character 403.Sq \e0 404after the end of the filename. 405Nice to 406.Xr cut 1 407the output. 408This does not affect the separator, which is still printed. 409.Pp 410If this option is repeated more than once, then 411.Nm 412prints just the filename followed by a NUL followed by the description 413(or ERROR: text) followed by a second NUL for each entry. 414.It Fl -help 415Print a help message and exit. 416.El 417.Sh ENVIRONMENT 418The environment variable 419.Ev MAGIC 420can be used to set the default magic file name. 421If that variable is set, then 422.Nm 423will not attempt to open 424.Pa $HOME/.magic . 425.Nm 426adds 427.Dq Pa .mgc 428to the value of this variable as appropriate. 429The environment variable 430.Ev POSIXLY_CORRECT 431controls (on systems that support symbolic links), whether 432.Nm 433will attempt to follow symlinks or not. 434If set, then 435.Nm 436follows symlink, otherwise it does not. 437This is also controlled by the 438.Fl L 439and 440.Fl h 441options. 442.Sh FILES 443.Bl -tag -width /usr/share/misc/magic.mgc -compact 444.It Pa /usr/share/misc/magic.mgc 445Default compiled list of magic. 446.It Pa /usr/share/misc/magic 447Directory containing default magic files. 448.El 449.Sh EXIT STATUS 450.Nm 451will exit with 452.Dv 0 453if the operation was successful or 454.Dv >0 455if an error was encountered. 456The following errors cause diagnostic messages, but don't affect the program 457exit code (as POSIX requires), unless 458.Fl E 459is specified: 460.Bl -bullet -compact -offset indent 461.It 462A file cannot be found 463.It 464There is no permission to read a file 465.It 466The file type cannot be determined 467.El 468.Sh EXAMPLES 469.Bd -literal -offset indent 470$ file file.c file /dev/{wd0a,hda} 471file.c: C program text 472file: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 473 dynamically linked (uses shared libs), stripped 474/dev/wd0a: block special (0/0) 475/dev/hda: block special (3/0) 476 477$ file -s /dev/wd0{b,d} 478/dev/wd0b: data 479/dev/wd0d: x86 boot sector 480 481$ file -s /dev/hda{,1,2,3,4,5,6,7,8,9,10} 482/dev/hda: x86 boot sector 483/dev/hda1: Linux/i386 ext2 filesystem 484/dev/hda2: x86 boot sector 485/dev/hda3: x86 boot sector, extended partition table 486/dev/hda4: Linux/i386 ext2 filesystem 487/dev/hda5: Linux/i386 swap file 488/dev/hda6: Linux/i386 swap file 489/dev/hda7: Linux/i386 swap file 490/dev/hda8: Linux/i386 swap file 491/dev/hda9: empty 492/dev/hda10: empty 493 494$ file -i file.c file /dev/{wd0a,hda} 495file.c: text/x-c 496file: application/x-executable 497/dev/hda: application/x-not-regular-file 498/dev/wd0a: application/x-not-regular-file 499 500.Ed 501.Sh SEE ALSO 502.Xr hexdump 1 , 503.Xr od 1 , 504.Xr strings 1 , 505.Xr magic 5 506.Sh STANDARDS CONFORMANCE 507This program is believed to exceed the System V Interface Definition 508of FILE(CMD), as near as one can determine from the vague language 509contained therein. 510Its behavior is mostly compatible with the System V program of the same name. 511This version knows more magic, however, so it will produce 512different (albeit more accurate) output in many cases. 513.\" URL: http://www.opengroup.org/onlinepubs/009695399/utilities/file.html 514.Pp 515The one significant difference 516between this version and System V 517is that this version treats any white space 518as a delimiter, so that spaces in pattern strings must be escaped. 519For example, 520.Bd -literal -offset indent 521\*[Gt]10 string language impress\ (imPRESS data) 522.Ed 523.Pp 524in an existing magic file would have to be changed to 525.Bd -literal -offset indent 526\*[Gt]10 string language\e impress (imPRESS data) 527.Ed 528.Pp 529In addition, in this version, if a pattern string contains a backslash, 530it must be escaped. 531For example 532.Bd -literal -offset indent 5330 string \ebegindata Andrew Toolkit document 534.Ed 535.Pp 536in an existing magic file would have to be changed to 537.Bd -literal -offset indent 5380 string \e\ebegindata Andrew Toolkit document 539.Ed 540.Pp 541SunOS releases 3.2 and later from Sun Microsystems include a 542.Nm 543command derived from the System V one, but with some extensions. 544This version differs from Sun's only in minor ways. 545It includes the extension of the 546.Sq \*[Am] 547operator, used as, 548for example, 549.Bd -literal -offset indent 550\*[Gt]16 long\*[Am]0x7fffffff \*[Gt]0 not stripped 551.Ed 552.Sh SECURITY 553On systems where libseccomp 554.Pa ( https://github.com/seccomp/libseccomp ) 555is available, 556.Nm 557is enforces limiting system calls to only the ones necessary for the 558operation of the program. 559This enforcement does not provide any security benefit when 560.Nm 561is asked to decompress input files running external programs with 562the 563.Fl z 564option. 565To enable execution of external decompressors, one needs to disable 566sandboxing using the 567.Fl S 568option. 569.Sh MAGIC DIRECTORY 570The magic file entries have been collected from various sources, 571mainly USENET, and contributed by various authors. 572Christos Zoulas (address below) will collect additional 573or corrected magic file entries. 574A consolidation of magic file entries 575will be distributed periodically. 576.Pp 577The order of entries in the magic file is significant. 578Depending on what system you are using, the order that 579they are put together may be incorrect. 580If your old 581.Nm 582command uses a magic file, 583keep the old magic file around for comparison purposes 584(rename it to 585.Pa /usr/share/misc/magic.orig ) . 586.Sh HISTORY 587There has been a 588.Nm 589command in every 590.Dv UNIX since at least Research Version 4 591(man page dated November, 1973). 592The System V version introduced one significant major change: 593the external list of magic types. 594This slowed the program down slightly but made it a lot more flexible. 595.Pp 596This program, based on the System V version, 597was written by Ian Darwin 598.Aq ian@darwinsys.com 599without looking at anybody else's source code. 600.Pp 601John Gilmore revised the code extensively, making it better than 602the first version. 603Geoff Collyer found several inadequacies 604and provided some magic file entries. 605Contributions of the 606.Sq \*[Am] 607operator by Rob McMahon, 608.Aq cudcv@warwick.ac.uk , 6091989. 610.Pp 611Guy Harris, 612.Aq guy@netapp.com , 613made many changes from 1993 to the present. 614.Pp 615Primary development and maintenance from 1990 to the present by 616Christos Zoulas 617.Aq christos@astron.com . 618.Pp 619Altered by Chris Lowth 620.Aq chris@lowth.com , 6212000: handle the 622.Fl i 623option to output mime type strings, using an alternative 624magic file and internal logic. 625.Pp 626Altered by Eric Fischer 627.Aq enf@pobox.com , 628July, 2000, 629to identify character codes and attempt to identify the languages 630of non-ASCII files. 631.Pp 632Altered by Reuben Thomas 633.Aq rrt@sc3d.org , 6342007-2011, to improve MIME support, merge MIME and non-MIME magic, 635support directories as well as files of magic, apply many bug fixes, 636update and fix a lot of magic, improve the build system, improve the 637documentation, and rewrite the Python bindings in pure Python. 638.Pp 639The list of contributors to the 640.Sq magic 641directory (magic files) 642is too long to include here. 643You know who you are; thank you. 644Many contributors are listed in the source files. 645.Sh LEGAL NOTICE 646Copyright (c) Ian F. Darwin, Toronto, Canada, 1986-1999. 647Covered by the standard Berkeley Software Distribution copyright; see the file 648COPYING in the source distribution. 649.Pp 650The files 651.Pa tar.h 652and 653.Pa is_tar.c 654were written by John Gilmore from his public-domain 655.Xr tar 1 656program, and are not covered by the above license. 657.Sh BUGS 658Please report bugs and send patches to the bug tracker at 659.Pa https://bugs.astron.com/ 660or the mailing list at 661.Aq file@astron.com 662(visit 663.Pa https://mailman.astron.com/mailman/listinfo/file 664first to subscribe). 665.Sh TODO 666Fix output so that tests for MIME and APPLE flags are not needed all 667over the place, and actual output is only done in one place. 668This needs a design. 669Suggestion: push possible outputs on to a list, then pick the 670last-pushed (most specific, one hopes) value at the end, or 671use a default if the list is empty. 672This should not slow down evaluation. 673.Pp 674The handling of 675.Dv MAGIC_CONTINUE 676and printing \e012- between entries is clumsy and complicated; refactor 677and centralize. 678.Pp 679Some of the encoding logic is hard-coded in encoding.c and can be moved 680to the magic files if we had a !:charset annotation. 681.Pp 682Continue to squash all magic bugs. 683See Debian BTS for a good source. 684.Pp 685Store arbitrarily long strings, for example for %s patterns, so that 686they can be printed out. 687Fixes Debian bug #271672. 688This can be done by allocating strings in a string pool, storing the 689string pool at the end of the magic file and converting all the string 690pointers to relative offsets from the string pool. 691.Pp 692Add syntax for relative offsets after current level (Debian bug #466037). 693.Pp 694Make file -ki work, i.e. give multiple MIME types. 695.Pp 696Add a zip library so we can peek inside Office2007 documents to 697print more details about their contents. 698.Pp 699Add an option to print URLs for the sources of the file descriptions. 700.Pp 701Combine script searches and add a way to map executable names to MIME 702types (e.g. have a magic value for !:mime which causes the resulting 703string to be looked up in a table). 704This would avoid adding the same magic repeatedly for each new 705hash-bang interpreter. 706.Pp 707When a file descriptor is available, we can skip and adjust the buffer 708instead of the hacky buffer management we do now. 709.Pp 710Fix 711.Dq name 712and 713.Dq use 714to check for consistency at compile time (duplicate 715.Dq name , 716.Dq use 717pointing to undefined 718.Dq name 719). 720Make 721.Dq name 722/ 723.Dq use 724more efficient by keeping a sorted list of names. 725Special-case ^ to flip endianness in the parser so that it does not 726have to be escaped, and document it. 727.Pp 728If the offsets specified internally in the file exceed the buffer size 729( 730.Dv HOWMANY 731variable in file.h), then we don't seek to that offset, but we give up. 732It would be better if buffer managements was done when the file descriptor 733is available so we can seek around the file. 734One must be careful though because this has performance and thus security 735considerations, because one can slow down things by repeatedly seeking. 736.Pp 737There is support now for keeping separate buffers and having offsets from 738the end of the file, but the internal buffer management still needs an 739overhaul. 740.Sh AVAILABILITY 741You can obtain the original author's latest version by anonymous FTP 742on 743.Pa ftp.astron.com 744in the directory 745.Pa /pub/file/file-X.YZ.tar.gz . 746