File
Autor
Jürgen Lätte
Rühm: AK21
05.01.16
Sissejuhatus
"File" käsk on Linuxi terminalis väga laialdaselt kasutatav. Seda seetõttu, et UNIX süsteemides on kõiki asju kirjeldatud failidena. Ei tehta vahet sellel, kas on fail või kataloog. Kataloog on lihtsalt üks fail, mis sisaldab endas nimekirjade teiste failide kohta. Süsteem peab failideks programme, teenuseid, tekste, pilte. Samuti loetakse failiks kõiki seadmeid, sealhulgas ka sisend ja väljundseadmeid. "File" käsuga määratakse ära, millise failitüübiga tegu on.
Selles artikis on lühiülevaade file kasutusvõimalustest ja nippidest. Juurde on lisatud ka täpsemad seletused ja näited.
Kasutamine
Ülevaade käskudest
Süntaks [1]
file [-bcdEhiklLNnprsvzZ0] [--apple] [--extension] [--mime-encoding]
[--mime-type] [-e testname] [-F separator] [-f namefile]
[-m magicfiles] [-P name=value] file ...
file -C [-m magicfiles]
file [--help]
Võimalused [2]
- b, --brief Do not prepend filenames to output lines (brief mode).
-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).
ascii 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 Ignored for backwards compatibility.
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 separator 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. Please note that namefile is unwrapped and the enclosed filenames are processed when this option is encountered and before any further options processing is done. This allows one to process multiple lists of files with different command line arguments on the same file invocation. Thus if you want to set the delimiter, you need to do it before you specify the list of files, like: "-F @ -f namefile", instead of: "-f namefile -F @".
-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".
--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, --list Print information about the strength of each magic pattern.
-L, --dereference option causes symlinks to be followed, as the like-named option in ls (on systems that support symbolic links). This is the default if the environment variable POSIXLY_CORRECT is defined.
-l Shows sorted patterns list in the order which is used for the matching.
-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 or utimes, 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 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 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, which is helpful if, for instance, you'd like to cut the output. This does not affect the separator which is still printed.
--help Print a help message and exit.
Sisestades history | less kuvatakse ühe lehekülje kaupa käskude ajalugu
Sisestades history | tail kuvatakse viimased kümme käsku
Käskude ajaloo kustutamine
Kui soovitakse, et käskude ajalugu ei salvestuks, tuleb .bash_profile failis teha vastav sisestus. Seda varianti kasutatakse tihti turvalisuse eesmärgil
vi .bash_profile # .bash_profile # Get the aliases and functions if [ -f ~/.bashrc ]; then . ~/.bashrc fi # User specific environment and startup programs export HISTCONTROL=ignoredups PATH=$PATH:$HOME/bin export PATH
Sisestades käsu export HISTSIZE=0 peatub ajaloo salvestamine
Sisestades käsu history -c puhastatakse kogu käskude ajalugu, kuid jätkub uute käskude salvestamine
Piirangud
Samuti on võimalik seada piiranguid, näiteks mitu rida salvestatake käske
vi ~/.bash_profile HISTSIZE=450 HISTFILESIZE=450
Üks huvitavatest võimalustest on ka varjata ühte konkreetset käsku. Selleks tuleb toimida järgnevalt
export HISTCONTROL=ignorespacels -ltr pwd service httpd stop (rea alguses olev tühik on väga oluline) history | tail -3
Käskude taasesitamine
Käskude ajaloost on võimalik ka taasesitada juba varem sisestatud käsku. Selleks tuleb kasutada hüüumärki ja reanumbrit kus käsk asub.
NÄIDE history | more 1 service network restart 2 exit 3 id 4 cat /etc/redhat-release !4 cat /etc/redhat-release
Ajalugu klaviatuurikombinatsioonidega
Kasutades klaviatuurinuppe on võimalik vaadata eelnevalt sisestatud käske ja neid taasesitada
1. Nool üles - ükshaaval käskude kuvamine tagasisuunas
2. Ctrl-p - ükshaaval käskude kuvamine tagasisuunas
3. ALT-Shift - võimalik tagasi liikuda kõige viimase ja käesoleva käsu vahel
4. Nool alla - ükshaaval käskude kuvamine edasisuunas
5. Ctrl-n - ükshaaval käskude kuvamine edasisuunas
Kokkuvõte
"History" käsku on mugav ja lihtne kasutada, kui on vaja uuesti sisestada pikki ja keerulisi käske. "History" käsuga on võimalik ka saada ülevaade sisestatud käskudest, mis võimaldab meelde tuletada ning üle vaadata tehtud töö.
