当今可能我们很多人已经不频繁使用man命令了，取而代之的是更加友好简单的tldr。
- $ tldr du |head
- du
- Disk usage: estimate and summarize file and directory space usage.
- - List the sizes of a directory and any subdirectories, in the given unit (B/KB/MB):
- du -{{b|k|m}} {{path/to/directory}}
- - List the sizes of a directory and any subdirectories, in human-readable form (i.e. auto-selecting the appropriate unit for each size):
- du -h {{path/to/directory}}r
- - Show the size of a single directory, in human readable units:
然而，man命令始终是我个人的最爱。每当心情低落时候，我就会中用man命令信步由缰的做各种查询。从中慢慢获得秩序感，全局的掌控感，低落的心情也慢慢疗愈。
man命令让我们与计算机对话沟通，又仿佛促使我们与计算机融为一体，人机合一。
1.man的9个章节
man可能是唯一一个可以自我陈述的命令。我们先从最直觉的使用方法开始。
- man man
从结果中，我们看到Manual手册共分为9个章节(sections)。似乎有点多，我们将归类为4个部分。
- 前三项是commands(shell-commands, system-calls,libraries)
- 接着是files(special-file,file-format)
- 然后是Miscellaneous, Game也放在这里
- 最后是System(Administation,Kernel)
2.存放地址
Linux系统中一切皆为文件，我们首先感兴趣的是，这些manual手册存放在哪里。根据前文 帮你精通Linux：透彻解析Linux的目录树结构 可以简单推测，
- 配置文件在/etc/目录下，具体则为/etc/manpath.config;
- 变量文件在/var/目录下，具体则为/var/cache/man/index.(bt|db|dir|pag)
/etc和/var是linux系统下的最重要的两个目录。
man文件本身存储在/usr/share目录下，/usr/share/man
如何查看特定命令的存储位置呢?需要 -w选项(对应长选项--where)
- $ man -w time
- /usr/share/man/man1/time.1.gz
加上选-a(对应--all)则能查到time在所有章节中的位置。
- $ man -aw time
- /usr/share/man/man1/time.1.gz
- /usr/share/man/man2/time.2.gz
- /usr/share/man/man7/time.7.gz
从结果中看到，在man1(shell commands), man2(system calls)和man7(Miscellaneous)中都有time这个命令。
作为补充，我们也可以用-f选项查看命令所属的sections。
- $ man -f man
- man (7) - macros to format man pages
- man (1) - an interface to the on-line reference manuals
-
- $ man -f time
- time (7) - overview of time and timers
- time (1) - run programs and summarize system resource usage
- time (2) - get time in seconds
此处的 -f 等价于--whatis
whatis (1) - display one-line manual page descriptions
3.指定查询章节
从 -w 选项中看到了命令的地址，便可以指定章节查询。
- whatis (1) - display one-line manual page descriptions
- man 7 time
4.正则查询
man命令最有意思的就是正则查询，心情不好的时候，可以玩上一整天。
从正则查询中，能够获得对全局的掌控感，比如查询systemd有多少个命令：
- $ man -k ^systemd |nl |tail
- 158 systemd.service (5) - Service unit configuration
- 159 systemd.slice (5) - Slice unit configuration
- 160 systemd.socket (5) - Socket unit configuration
- 161 systemd.special (7) - Special systemd units
- 162 systemd.swap (5) - Swap unit configuration
- 163 systemd.syntax (7) - General syntax of systemd configuration files
- 164 systemd.target (5) - Target unit configuration
- 165 systemd.time (7) - Time and date specifications
- 166 systemd.timer (5) - Timer unit configuration
- 167 systemd.unit (5) - Unit configuration
从结果中国马上获知167这个结果。
或者查询有多少与calendar相关的命令：
- $ man -k calendar |nl
- 1 cal (1) - displays a calendar and the date of Easter
- 2 calendar (1) - reminder service
- 3 ncal (1) - displays a calendar and the date of Easter
又或者查询全部的ls命令：
- $ man -k ^ls |nl
- 1 ls (1) - list directory contents
- 2 lsar (1) - list archive file contents
- 3 lsattr (1) - list file attributes on a Linux second extended file system
- 4 lsb_release (1) - print distribution-specific information
- 5 lsblk (8) - list block devices
- 6 lscpu (1) - display information about the CPU architecture
- 7 lsearch (3) - linear search of an array
- 8 lseek (2) - reposition read/write file offset
- 9 lseek64 (3) - reposition 64-bit read/write file offset
- 10 lsetxattr (2) - set an extended attribute value
- 11 lshw (1) - list hardware
- 12 lsinitramfs (8) - list content of an initramfs image
- 13 lsipc (1) - show information on IPC facilities currently employed in ...
- 14 lslocks (8) - list local system locks
- 15 lslogins (1) - display information about known users in the system
- 16 lsmem (1) - list the ranges of available memory with their online status
- 17 lsmod (8) - Show the status of modules in the Linux Kernel
- 18 lsns (8) - list namespaces
- 19 lsof (8) - list open files
- 20 lspci (8) - list all PCI devices
- 21 lspcmcia (8) - display extended PCMCIA debugging information
- 22 lspgpot (1) - extracts the ownertrust values from PGP keyrings and list...
- 23 lstat (2) - get file status
- 24 lstat64 (2) - get file status
- 25 lsusb (8) - list USB devices
5.全局掌控
文章开头就介绍过section 2 中是system-calls命令。我们不免心生好奇，哪些是system-calls呢?
- $ man -s 2 -k . |nl |tail
- 484 vm86old (2) - enter virtual 8086 mode
- 485 vmsplice (2) - splice user pages to/from a pipe
- 486 vserver (2) - unimplemented system calls
- 487 wait (2) - wait for process to change state
- 488 wait3 (2) - wait for process to change state, BSD style
- 489 wait4 (2) - wait for process to change state, BSD style
- 490 waitid (2) - wait for process to change state
- 491 waitpid (2) - wait for process to change state
- 492 write (2) - write to a file descriptor
- 493 writev (2) - read or write data into multiple buffers
由上可知，系统中共有493个system-calls。我们分析下这一行命令：
- man -s 2 -k .
短选代表的是长选项--section，-k 是 keyword，等价于 apropos命令，最后的 dot 点 乃是正则表达式里的任意字符的表达方式。
于是，仅仅通过上面的简单命令获得对整个文档乃至整台计算机，整个计算机科学的全局掌控感。我们迅速掠览一遍这9个sections。
Section 1 Shell Commands系统命令：
- $ man -s 1 -k . |nl| tail -n 5
- 2451 zless (1) - file perusal filter for crt viewing of compressed text
- 2452 zlib_decompress (1) - decompress mysqlpump ZLIB-compressed output
- 2453 zmore (1) - file perusal filter for crt viewing of compressed text
- 2454 znew (1) - recompress .Z files to .gz files
- 2455 zsoelim (1) - satisfy .so requests in roff input
Section 2 Syetem Calls系统调用
- $ man -s 2 -k . |nl| tail -n 5
- 489 wait4 (2) - wait for process to change state, BSD style
- 490 waitid (2) - wait for process to change state
- 491 waitpid (2) - wait for process to change state
- 492 write (2) - write to a file descriptor
- 493 writev (2) - read or write data into multiple buffers
Section 3 C LIbraries C语库
- $ man -s 3 -k . |nl| tail -n 5
- 1899 y1l (3) - Bessel functions of the second kind
- 1900 yn (3) - Bessel functions of the second kind
- 1901 ynf (3) - Bessel functions of the second kind
- 1902 ynl (3) - Bessel functions of the second kind
- 1903 zlib (3) - compression/decompression library
Section 4 Special Files 特殊文件
- $ man -s 4 -k . |nl| tail -n 5
- 48 veth (4) - Virtual Ethernet Device
- 49 vmware (4) - VMware SVGA video driver
- 50 wacom (4) - Wacom input driver
- 51 wavelan (4) - AT&T GIS WaveLAN ISA device driver
- 52 zero (4) - data sink
Secion 5 File Format and conventions 文件格式及惯例
- $ man -s 5 -k . |nl| tail -n 5
- 424 xorg.conf (5) - configuration files for Xorg X server
- 425 xorg.conf.d (5) - configuration files for Xorg X server
- 426 Xsession (5) - initialize X session
- 427 Xsession.options (5) - configuration options for Xsession (5)
- 428 Xwrapper.config (5) - Xorg X server binary wrapper
Secion 6 Games 游戏
- $ man -s 6 -k . |nl| tail -n 5
- 1 intro (6) - introduction to games
- 2 kmahjongg (6) - Mahjongg game for KDE
- 3 kmines (6) - KDE mine sweeper game
- 4 kpat (6) - A highly addictive card game.
- 5 ksudoku (6) - KDE Sudoku games
Section 7 Miscellaneous (including macro packages and conventions)杂项
- $ man -s 7 -k . |nl| tail -n 5
- 470 XConsortium (7) - X Consortium information
- 471 xkeyboard-config (7) - XKB data description files
- 472 XOrgFoundation (7) - X.Org Foundation information
- 473 Xsecurity (7) - X display access control
- 474 XStandards (7) - X Window System Standards and Specifications
Section 8 System administration commands (usually only for root)系统管理命令
- $ man -s 8 -k . |nl| tail -n 5
- 890 xtables-nft-multi (8) - iptables using nftables kernel api
- 891 xtables-translate (8) - translation tool to migrate from iptables to nftables
- 892 zdump (8) - timezone dumper
- 893 zic (8) - timezone compiler
- 894 zramctl (8) - set up and control zram devices
Section 9 Kernel routines [Non standard] 内核函数
- ➜ ~ man -s 9 -k .
- vmxnet (9) - vmware kernel module
掌控全局还有另外一种方法，就是intro命令：
- $ man -f intro
- intro (8) - introduction to administration and privileged commands
- intro (7) - introduction to overview and miscellany section
- intro (3) - introduction to library functions
- intro (4) - introduction to special files
- intro (1) - introduction to user commands
- intro (5) - introduction to file formats and filesystems
- intro (6) - introduction to games
- intro (2) - introduction to system calls
我们看到每个section都有一个intro。
比如我们查看section 2的intro：
6.游戏
man命令有良好的疗愈功效，不妨来看看Kubuntu自带的四个游戏。
- $ man -s 6 -k . |nl
- 1 intro (6) - introduction to games
- 2 kmahjongg (6) - Mahjongg game for KDE
- 3 (6) - KDE mine sweeper game
- 4 kpat (6) - A highly addictive card game.
- 5 ksudoku (6) - KDE Sudoku games
7.收尾总结
man命令是我们最好的陪伴，帮助满血复活对工作和生活的掌控感。
