六个优雅的Linux命令行技巧
- 一些非常有用的命令能让命令行的生活更满足
使用 Linux 命令工作可以获得许多乐趣，但是如果您使用一些命令，它们可以减少您的工作或以有趣的方式显示信息时，您将获得更多的乐趣。在今天的文章中，我们将介绍六个命令，它们可能会使你用在命令行上的时间更加值当。
watch
watch 命令会重复运行您给出的任何命令，并显示输出。默认情况下，它每两秒运行一次命令。命令的每次运行都将覆盖上一次运行时显示的内容，因此您始终可以看到最新的数据。
您可能会在等待某人登录时使用它。在这种情况下，您可以使用 watch who 命令或者 watch -n 15 who 命令使每 15 秒运行一次，而不是两秒一次。另外终端窗口的右上角会显示日期和时间。
$ watch -n 5 who Every 5.0s: who stinkbug: Wed Aug 23 14:52:15 2017 shs pts/0 2017-08-23 14:45 (192.168.0.11) zoe pts/1 2017-08-23 08:15 (192.168.0.19)
您也可以使用它来查看日志文件。如果您显示的数据没有任何变化，则只有窗口角落里的日期和时间会发生变化。
$ watch tail /var/log/syslog Every 2.0s: tail /var/log/syslog stinkbug: Wed Aug 23 15:16:37 2017 Aug 23 14:45:01 stinkbug CRON[7214]: (root) CMD (command -v debian-sa1 > /dev/nu ll && debian-sa1 1 1) Aug 23 14:45:17 stinkbug systemd[1]: Started Session 179 of user shs. Aug 23 14:55:01 stinkbug CRON[7577]: (root) CMD (command -v debian-sa1 > /dev/nu ll && debian-sa1 1 1) Aug 23 15:05:01 stinkbug CRON[7582]: (root) CMD (command -v debian-sa1 > /dev/nu ll && debian-sa1 1 1) Aug 23 15:08:48 stinkbug systemd[1]: Starting Cleanup of Temporary Directories... Aug 23 15:08:48 stinkbug systemd-tmpfiles[7584]: [/usr/lib/tmpfiles.d/var.conf:1 4] Duplicate line for path "/var/log", ignoring. Aug 23 15:08:48 stinkbug systemd[1]: Started Cleanup of Temporary Directories. Aug 23 15:13:41 stinkbug systemd[1]: Started Session 182 of user shs. Aug 23 15:14:29 stinkbug systemd[1]: Started Session 183 of user shs. Aug 23 15:15:01 stinkbug CRON[7828]: (root) CMD (command -v debian-sa1 > /dev/nu ll && debian-sa1 1 1)
这里的输出和使用命令 tail -f /var/log/syslog 的输出相似。
look
这个命令的名字 look 可能会让我们以为它和 watch 做类似的事情，但其实是不同的。look 命令用于搜索以某个特定字符串开头的单词。
$ look ecl eclectic eclectic's eclectically eclecticism eclecticism's eclectics eclipse eclipse's eclipsed eclipses eclipsing ecliptic ecliptic's
look 命令通常有助于单词的拼写，它使用 /usr/share/dict/words 文件，除非你使用如下的命令指定了文件名：
$ look esac .bashrc esac esac esac
在这种情况下，它的作用就像跟在一个 awk 命令后面的 grep ，只打印匹配行上的第一个单词。
man -k
man -k 命令列出包含指定单词的手册页。它的工作基本上和 apropos 命令一样。
$ man -k logrotate dh_installlogrotate (1) - install logrotate config files logrotate (8) - rotates, compresses, and mails system logs logrotate.conf (5) - rotates, compresses, and mails system logs
help
当你完全绝望的时候，您可能会试图使用此命令，help 命令实际上是显示一个 shell 内置命令的列表。最令人惊讶的是它有相当多的参数变量。你可能会看到这样的东西，然后开始想知道这些内置功能可以为你做些什么：
$ help
GNU bash, version 4.4.7(1)-release (i686-pc-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 hist>
(( expression )) if COMMANDS; then COMMANDS; [ elif C>
. filename [arguments] jobs [-lnprs] [jobspec ...] or jobs >
: kill [-s sigspec | -n signum | -sigs>
[ arg... ] let arg [arg ...]
[[ expression ]] local [option] name[=value] ...
alias [-p] [name[=value] ... ] logout [n]
bg [job_spec ...] mapfile [-d delim] [-n count] [-O or>
bind [-lpsvPSVX] [-m keymap] [-f file> 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] [->
cd [-L|[-P [-e]] [-@]] [dir] readarray [-n count] [-O origin] [-s>
command [-pVv] command [arg ...] readonly [-aAf] [name[=value] ...] o>
compgen [-abcdefgjksuv] [-o option] [> return [n]
complete [-abcdefgjksuv] [-pr] [-DE] > select NAME [in WORDS ... ;] do COMM>
compopt [-o|+o option] [-DE] [name ..> set [-abefhkmnptuvxBCHP] [-o option->
continue [n] shift [n]
coproc [NAME] command [redirections] shopt [-pqsu] [-o] [optname ...]
declare [-aAfFgilnrtux] [-p] [name[=v> source filename [arguments]
dirs [-clpv] [+N] [-N] suspend [-f]
disown [-h] [-ar] [jobspec ... | pid > test [expr]
echo [-neE] [arg ...] time [-p] pipeline
enable [-a] [-dnps] [-f filename] [na> times
eval [arg ...] trap [-lp] [[arg] signal_spec ...]
exec [-cl] [-a name] [command [argume> true
exit [n] type [-afptP] name [name ...]
export [-fn] [name[=value] ...] or ex> typeset [-aAfFgilnrtux] [-p] name[=v>
false ulimit [-SHabcdefiklmnpqrstuvxPT] [l>
fc [-e ename] [-lnr] [first] [last] o> umask [-p] [-S] [mode]
fg [job_spec] unalias [-a] name [name ...]
for NAME [in WORDS ... ] ; do COMMAND> unset [-f] [-v] [-n] [name ...]
for (( exp1; exp2; exp3 )); do COMMAN> until COMMANDS; do COMMANDS; done
function name { COMMANDS ; } or name > variables - Names and meanings of so>
getopts optstring name [arg] wait [-n] [id ...]
hash [-lr] [-p pathname] [-dt] [name > while COMMANDS; do COMMANDS; done
help [-dms] [pattern ...] { COMMANDS ; } stat -c
stat 命令用于显示文件的大小、所有者、用户组、索引节点号、权限、修改和访问时间等重要的统计信息。这是一个非常有用的命令，可以显示比 ls -l 更多的细节。
$ stat .bashrc File: .bashrc Size: 4048 Blocks: 8 IO Block: 4096 regular file Device: 806h/2054d Inode: 421481 Links: 1 Access: (0644/-rw-r--r--) Uid: ( 1000/ shs) Gid: ( 1000/ shs) Access: 2017-08-23 15:13:41.781809933 -0400 Modify: 2017-06-21 17:37:11.875157790 -0400 Change: 2017-06-21 17:37:11.899157791 -0400 Birth: -
使用 -c 选项，您可以指定要查看的字段。例如，如果您只想查看一个文件或一系列文件的文件名和访问权限，则可以这样做：
$ stat -c '%n %a' .bashrc .bashrc 644
在此命令中， %n 表示每个文件的名称，而 %a 表示访问权限。%u 表示数字类型的 UID，而 %U 表示用户名。
$ stat -c '%n %a' bin/* bin/loop 700 bin/move2nohup 700 bin/nohup.out 600 bin/show_release 700 $ stat -c '%n %a %U' bin/* bin/loop 700 shs bin/move2nohup 700 shs bin/nohup.out 600 root bin/show_release 700 shs
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