9、在linux系統下獲取幫助
本節主要學習在linux系統下如何獲取和使用幫助，這些命令有help、man、info等。
9.1 help：
可以查看內部Shell命令的幫助信息。
9.1.1 命令語法：
help[選項][命令]
9.1.2選項參數：
help命令選項含義:
-d 顯示命令簡短的主題描述
-s 顯示命令簡短的語法描述
9.1.3 實例：
例1：查看能使用help命令查看幫助信息的命令。
[root@ser01 ~]# help
GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
These shell commands are defined internally. Type `help' to see this list.
Type `help name' to find out more about the function `name'.
Use `info bash' to find out more about the shell in general.
Use `man -k' or `info' to find out more about commands not in this list.
A star (*) next to a name means that the command is disabled.
job_spec [&] history [-c] [-d offset] [n] or histo>
(( expression )) if COMMANDS; then COMMANDS; [ elif CO>
. filename [arguments] jobs [-lnprs] [jobspec ...] or jobs ->
: kill [-s sigspec | -n signum | -sigsp>
[ arg... ] let arg [arg ...]
` expression ` local [option] name[=value] ...
alias [-p] [name[=value] ... ] logout [n]
bg [job_spec ...] mapfile [-n count] [-O origin] [-s co>
bind [-lpvsPVS] [-m keymap] [-f filena> popd [-n] [+N | -N]
break [n] printf [-v var] format [arguments]
builtin [shell-builtin [arg ...]] pushd [-n] [+N | -N | dir]
caller [expr] pwd [-LP]
case WORD in [PATTERN [| PATTERN]...) > read [-ers] [-a array] [-d delim] [-i>
cd [-L|-P] [dir] readarray [-n count] [-O origin] [-s >
command [-pVv] command [arg ...] readonly [-af] [name[=value] ...] or >
compgen [-abcdefgjksuv] [-o option] [> return [n]
complete [-abcdefgjksuv] [-pr] [-DE] [> select NAME [in WORDS ... ;] do COMMA>
compopt [-o|+o option] [-DE] [name ...> set [--abefhkmnptuvxBCHP] [-o option->
continue [n] shift [n]
coproc [NAME] command [redirections] shopt [-pqsu] [-o] [optname ...]
declare [-aAfFilrtux] [-p] [name[=valu> source filename [arguments]
dirs [-clpv] [+N] [-N] suspend [-f]
disown [-h] [-ar] [jobspec ...] test [expr]
echo [-neE] [arg ...] time [-p] pipeline
enable [-a] [-dnps] [-f filename] [nam> times
eval [arg ...] trap [-lp] [[arg] signal_spec ...]
exec [-cl] [-a name] [command [argumen> true
exit [n] type [-afptP] name [name ...]
export [-fn] [name[=value] ...] or exp> typeset [-aAfFilrtux] [-p] name[=valu>
false ulimit [-SHacdefilmnpqrstuvx] [limit]>
fc [-e ename] [-lnr] [first] [last] or> umask [-p] [-S] [mode]
fg [job_spec] unalias [-a] name [name ...]
for NAME [in WORDS ... ] ; do COMMANDS> unset [-f] [-v] [name ...]
for (( exp1; exp2; exp3 )); do COMMAND> until COMMANDS; do COMMANDS; done
function name { COMMANDS ; } or name (> variables - Names and meanings of som>
getopts optstring name [arg] wait [id]
hash [-lr] [-p pathname] [-dt] [name .> while COMMANDS; do COMMANDS; done
help [-dms] [pattern ...] { COMMANDS ; }
例2：使用help命令查看pwd命令詳細的幫助信息。
[root@ser01 ~]# help pwd
pwd: pwd [-LP]
Print the name of the current working directory.
Options:
-L print the value of $PWD if it names the current working
directory
-P print the physical directory, without any symbolic links
By default, `pwd' behaves as if `-L' were specified.
Exit Status:
Returns 0 unless an invalid option is given or the current directory
cannot be read.
例3：使用help命令查看pwd命令簡短的語法描述。
[root@ser01 ~]# help -s pwd
pwd: pwd [-LP]
例4：使用help命令查看pwd命令簡短的主題描述。
[root@ser01 ~]# help -d pwd
pwd - Print the name of the current working directory.
9.2 man：
可以用來查看命令、函數或者是文件的幫助手冊，另外它還可以顯示一些gzip壓縮格式的文件。
一般情況下man手冊頁的資源主要位於/usr/share/man目錄下。
注：
man手冊頁類型
類型： 描述：
1 用戶命令
2 系統調用
3 C語言函數庫
4 設備和特殊文件
5 文件格式和約定
6 遊戲程序
7 雜記
8 系統管理工具
9 Linux內核API（內核調用）
man手冊頁組成內容
手冊頁內容： 描述：
Header 標題
NAME 命令/函數的功能概述
SYNOPSIS 命令/函數用法的簡單描述
AVAILABILITY 可用性說明
DESCRIPTION 命令/函數的詳細描述
OPTIONS 該命令的所有可選項的詳細說明
RETURN VALUE 如果是函數，則列出函數返回值
ERRORS 如果函數調用出錯，則列出所有出錯的值和可能引起錯誤的原因
FILES 該命令/函數所用到的相關係統文件
ENVIRONMENT 和該命令/函數相關的環境變量
NOTES 表示不常用的用法或實現的細節
BUGS 已知的錯誤和警告
HISTORY 該命令/函數的歷史發展
SEE ALSO 可以參照的其他的相關命令/函數
Others 和一些具體命名/函數有關的特殊信息
EXAMPLES 命令/函數的示例
9.2.1 命令語法：
man[選項][名稱]
9.2.2 選項參數：
選項： 選項含義：
-M<路徑> 指定man手冊頁的搜索路徑
-a 顯示所有的手冊頁，而不是隻顯示第一個
-d 主要用於檢查，如果用戶加入了一個新的文件，就可以用這個選項檢查是否出錯，這個選項並不會列出文件內容
-f 只顯示出命令的功能而不顯示詳細的說明文件，和whatis命令功能一樣
-p 字符串設定運行的預先處理程序的順序
-w 不顯示手冊頁內容，只顯示將被格式化和顯示的文件所在位置
9.2.3 實例：
例1：顯示pwd命令的man手冊頁。
[root@docekr ~]# man pwd
PWD(1) User Commands PWD(1)
NAME //名稱
pwd - print name of current/working directory
SYNOPSIS //內容簡介
pwd [OPTION]...
DESCRIPTION //描述
Print the full filename of the current working directory.
-L, --logical
use PWD from environment, even if it contains symlinks
-P, --physical
avoid all symlinks
--help display this help and exit
--version
output version information and exit
NOTE: your shell may have its own version of pwd, which usually super‐
sedes the version described here. Please refer to your shell's documen‐
tation for details about the options it supports.
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Report pwd translation bugs to <http://translationproject.org/team/>
AUTHOR //作者
Written by Jim Meyering.
COPYRIGHT //版權聲明
Copyright ? 2013 Free Software Foundation, Inc. License GPLv3+: GNU GPL
version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it. There
is NO WARRANTY, to the extent permitted by law.
SEE ALSO //可參考內容
getcwd(3)
The full documentation for pwd is maintained as a Texinfo manual. If the
info and pwd programs are properly installed at your site, the command
info coreutils 'pwd invocation'
should give you access to the complete manual.
GNU coreutils 8.22 June 2014 PWD(1)
Manual page pwd(1) line 26/53 (END) (press h for help or q to quit)
sedes the version described here. Please refer to your shell's documen‐
tation for details about the options it supports.
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Report pwd translation bugs to <http://translationproject.org/team/>
AUTHOR
Written by Jim Meyering.
COPYRIGHT
Copyright ? 2013 Free Software Foundation, Inc. License GPLv3+: GNU GPL
version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it. There
is NO WARRANTY, to the extent permitted by law.
SEE ALSO
getcwd(3)
The full documentation for pwd is maintained as a Texinfo manual. If the
info and pwd programs are properly installed at your site, the command
info coreutils 'pwd invocation'
should give you access to the complete manual.
GNU coreutils 8.22 June 2014 PWD(1)
~
例2：查看/etc/passwd文件的man手冊頁
[root@docekr ~]# man 1 passwd
PASSWD(1) User utilities PASSWD(1)
NAME
passwd - update user's authentication tokens
SYNOPSIS
passwd [-k] [-l] [-u [-f]] [-d] [-e] [-n mindays] [-x maxdays] [-w warndays] [-i inactivedays] [-S] [--stdin] [username]
DESCRIPTION
The passwd utility is used to update user's authentication token(s).
This task is achieved through calls to the Linux-PAM and Libuser API. Essentially, it initializes itself as a "passwd" service with Linux-PAM and utilizes configured password modules to authenticate and then update a
user's password.
A simple entry in the global Linux-PAM configuration file for this service would be:
#
# passwd service entry that does strength checking of
# a proposed password before updating it.
#
passwd password requisite pam_cracklib.so retry=3
passwd password required pam_unix.so use_authtok
#
Note, other module types are not required for this application to function correctly.
OPTIONS
-k, --keep
The option -k is used to indicate that the update should only be for expired authentication tokens (passwords); the user wishes to keep their non-expired tokens as before.
-l, --lock
This option is used to lock the password of specified account and it is available to root only. The locking is performed by rendering the encrypted password into an invalid string (by prefixing the encrypted string
with an !). Note that the account is not fully locked - the user can still log in by other means of authentication such as the ssh public key authentication. Use chage -E 0 user command instead for full account lock‐
ing.
--stdin
This option is used to indicate that passwd should read the new password from standard input, which can be a pipe.
-u, --unlock
This is the reverse of the -l option - it will unlock the account password by removing the ! prefix. This option is available to root only. By default passwd will refuse to create a passwordless account (it will not
unlock an account that has only "!" as a password). The force option -f will override this protection.
-d, --delete
This is a quick way to delete a password for an account. It will set the named account passwordless. Available to root only.
-e, --expire
This is a quick way to expire a password for an account. The user will be forced to change the password during the next login attempt. Available to root only.
-f, --force
Force the specified operation.
-n, --minimum DAYS
This will set the minimum password lifetime, in days, if the user's account supports password lifetimes. Available to root only.
-x, --maximum DAYS
This will set the maximum password lifetime, in days, if the user's account supports password lifetimes. Available to root only.
-w, --warning DAYS
This will set the number of days in advance the user will begin receiving warnings that her password will expire, if the user's account supports password lifetimes. Available to root only.
-i, --inactive DAYS
This will set the number of days which will pass before an expired password for this account will be taken to mean that the account is inactive and should be disabled, if the user's account supports password life‐
times. Available to root only.
-S, --status
This will output a short information about the status of the password for a given account. Available to root user only.
Remember the following two principles
Protect your password.
Don't write down your password - memorize it. In particular, don't write it down and leave it anywhere, and don't place it in an unencrypted file! Use unrelated passwords for systems controlled by different organi‐
zations. Don't give or share your password, in particular to someone claiming to be from computer support or a vendor. Don't let anyone watch you enter your password. Don't enter your password to a computer you
don't trust or if things "look funny"; someone may be trying to hijack your password. Use the password for a limited time and change it periodically.
Choose a hard-to-guess password.
passwd through the calls to the pam_cracklib PAM module will try to prevent you from choosing a really bad password, but it isn't foolproof; create your password wisely. Don't use something you'd find in a dictio‐
nary (in any language or jargon). Don't use a name (including that of a spouse, parent, child, pet, fantasy character, famous person, and location) or any variation of your personal or account name. Don't use
accessible information about you (such as your phone number, license plate, or social security number) or your environment. Don't use a birthday or a simple pattern (such as "qwerty", "abc", or "aaa"). Don't use
any of those backwards, followed by a digit, or preceded by a digit. Instead, use a mixture of upper and lower case letters, as well as digits or punctuation. When choosing a new password, make sure it's unrelated
to any previous password. Use long passwords (say at least 8 characters long). You might use a word pair with punctuation inserted, a passphrase (an understandable sequence of words), or the first letter of each
word in a passphrase.
These principles are partially enforced by the system, but only partly so. Vigilance on your part will make the system much more secure.
EXIT CODE
On successful completion of its task, passwd will complete with exit code 0. An exit code of 1 indicates an error occurred. Textual errors are written to the standard error stream.
CONFORMING TO
Linux-PAM (Pluggable Authentication modules for Linux).
FILES
/etc/pam.d/passwd - the Linux-PAM configuration file
BUGS
None known.
SEE ALSO
pam(8), pam.d(5), libuser.conf(5), and pam_chauthtok(3).
For more complete information on how to configure this application with Linux-PAM, see the Linux-PAM System Administrators' Guide.
AUTHOR
Cristian Gafton <[email protected]>
GNU/Linux Jun 20 2012 PASSWD(1)
例3：顯示passwd命令和/etc/passwd文件手冊頁所在位置。
[root@docekr ~]# man -w passwd
/usr/share/man/man1/passwd.1.gz
9.3 info
它可以用來查看幫助信息，支持鏈接跳轉功能，info文檔都存放在/usr/share/info目錄中。
9.3.1命令語法：
info[選項][菜單項目]
9.3.2 選項參數：
info命令選項參數
選項 選項含義
-w 顯示info文檔的物理位置
-f<info文件> 指定要訪問的info文件
-o<文件> 將選中的節點全輸出到指定文件
-w 顯示info文件在系統中的位置
-n<節點> 在首個瀏覽過的info文件中指定節點
-O 跳轉至命令行選項節點
9.3.3 實例：
例1：查看linux系統中info文檔的分類列表
[root@docekr ~]# info
Libraries
* History: (history). The GNU history library API.
* RLuserman: (rluserman). The GNU readline library User's Manual.
Localization
* idn: (libidn)Invoking idn. Internationalized Domain Name (IDN) string
conversion.
Software development
* As: (as). The GNU assembler.
* Binutils: (binutils). The GNU binary utilities.
* Gas: (as). The GNU assembler.
* Ld: (ld). The GNU linker.
* Make: (make). The GNU make utility.
* gprof: (gprof). Profiling your program's execution
Software libraries
* libidn: (libidn). Internationalized string processing library.
System administration
* Which: (which). Show full path of commands.
* parted: (parted). GNU partitioning software
Texinfo documentation system
* Info: (info). Documentation browsing system.
Miscellaneous
* bash: (bash). The Bourne Again Shell.
Text creation and manipulation
* Diffutils: (diffutils). Comparing and merging files.
* Gawk: (gawk). A text scanning and processing language.
* grep: (grep). Print lines matching a pattern.
* sed: (sed). Stream EDitor.
-----Info: (dir)Top, 295 lines --Bot------------------------------------------------
例2：查看ls命令的info文檔
[root@docekr ~]# info ls
File: coreutils.info, Node: cp invocation, Next: dd invocation, Up: Basic operations
11.1 'cp': Copy files and directories
=====================================
'cp' copies files (or, optionally, directories). The copy is completely
independent of the original. You can either copy one file to another,
or copy arbitrarily many files to a destination directory. Synopses:
cp [OPTION]... [-T] SOURCE DEST
cp [OPTION]... SOURCE... DIRECTORY
cp [OPTION]... -t DIRECTORY SOURCE...
* If two file names are given, 'cp' copies the first file to the
second.
* If the '--target-directory' ('-t') option is given, or failing that
if the last file is a directory and the '--no-target-directory'
('-T') option is not given, 'cp' copies each SOURCE file to the
specified directory, using the SOURCEs' names.
Generally, files are written just as they are read. For exceptions,
see the '--sparse' option below.
By default, 'cp' does not copy directories. However, the '-R', '-a',
and '-r' options cause 'cp' to copy recursively by descending into
source directories and copying files to corresponding destination
directories.
When copying from a symbolic link, 'cp' normally follows the link
only when not copying recursively or when '--link' ('-l') is used. This
default can be overridden with the '--archive' ('-a'), '-d',
'--dereference' ('-L'), '--no-dereference' ('-P'), and '-H' options. If
more than one of these options is specified, the last one silently
overrides the others.
When copying to a symbolic link, 'cp' follows the link only when it
refers to an existing regular file. However, when copying to a dangling
symbolic link, 'cp' refuses by default, and fails with a diagnostic,
since the operation is inherently dangerous. This behavior is contrary
to historical practice and to POSIX. Set 'POSIXLY_CORRECT' to make 'cp'
attempt to create the target of a dangling destination symlink, in spite
of the possible risk. Also, when an option like '--backup' or '--link'
acts to rename or remove the destination before copying, 'cp' renames or
removes the symbolic link rather than the file it points to.
By default, 'cp' copies the contents of special files only when not
copying recursively. This default can be overridden with the
'--copy-contents' option.
'cp' generally refuses to copy a file onto itself, with the following
exception: if '--force --backup' is specified with SOURCE and DEST
identical, and referring to a regular file, 'cp' will make a backup
file, either regular or numbered, as specified in the usual ways (*note
Backup options::). This is useful when you simply want to make a backup
of an existing file before changing it.
The program accepts the following options. Also see *note Common
options::.
'-a'
'--archive'
Preserve as much as possible of the structure and attributes of the
original files in the copy (but do not attempt to preserve internal
directory structure; i.e., 'ls -U' may list the entries in a copied
directory in a different order). Try to preserve SELinux security
context and extended attributes (xattr), but ignore any failure to
--zz-Info: (coreutils.info.gz)cp invocation, 392 lines --Top-----------
例3：顯示ls命令info文檔的物理位置
[root@docekr ~]# info -w ls
/usr/share/info/coreutils.info.gz