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240 lines
14 KiB
Markdown
Half a dozen clever Linux command line tricks
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============================================================
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### Some very useful commands for making life on the command line more rewarding
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[Micah Elizabeth Scott][32] [(CC BY 2.0)][33]RELATED
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Working on the Linux command can be a lot of fun, but it can be even more fun when you use commands that take less work on your part or display information in interesting and useful ways. In today’s post, we’re going to look at half a dozen commands that might make your time on the command line more profitable.
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### watch
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The watch command will repeatedly run whatever command you give it and show you the output. By default, it runs the command every two seconds. Each successive running of the command overwrites what it displayed on the previous run, so you're always looking at the latest data.
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You might use it when you’re waiting for someone to log in. In this case, you would use the command “watch who” or maybe “watch -n 15 who” to have the command run every 15 seconds instead of every two seconds. The date and time will appear in the upper right-hand corner of your terminal window.
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```
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$ watch -n 5 who
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Every 5.0s: who stinkbug: Wed Aug 23 14:52:15 2017
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shs pts/0 2017-08-23 14:45 (192.168.0.11)
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zoe pts/1 2017-08-23 08:15 (192.168.0.19)
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```
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You might also use it to watch a log file. If nothing changes in the data you’re displaying, only the date/time display in the corner of the window will change.
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```
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$ watch tail /var/log/syslog
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Every 2.0s: tail /var/log/syslog stinkbug: Wed Aug 23 15:16:37 2017
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Aug 23 14:45:01 stinkbug CRON[7214]: (root) CMD (command -v debian-sa1 > /dev/nu
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ll && debian-sa1 1 1)
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Aug 23 14:45:17 stinkbug systemd[1]: Started Session 179 of user shs.
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Aug 23 14:55:01 stinkbug CRON[7577]: (root) CMD (command -v debian-sa1 > /dev/nu
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ll && debian-sa1 1 1)
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Aug 23 15:05:01 stinkbug CRON[7582]: (root) CMD (command -v debian-sa1 > /dev/nu
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ll && debian-sa1 1 1)
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Aug 23 15:08:48 stinkbug systemd[1]: Starting Cleanup of Temporary Directories...
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Aug 23 15:08:48 stinkbug systemd-tmpfiles[7584]: [/usr/lib/tmpfiles.d/var.conf:1
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4] Duplicate line for path "/var/log", ignoring.
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Aug 23 15:08:48 stinkbug systemd[1]: Started Cleanup of Temporary Directories.
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Aug 23 15:13:41 stinkbug systemd[1]: Started Session 182 of user shs.
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Aug 23 15:14:29 stinkbug systemd[1]: Started Session 183 of user shs.
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Aug 23 15:15:01 stinkbug CRON[7828]: (root) CMD (command -v debian-sa1 > /dev/nu
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ll && debian-sa1 1 1)
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```
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This output is similar to what you’d see using tail -f /var/log/syslog.
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### look
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The name might suggest that look does something similar to watch, but it’s entirely different. The look command searches for words that begin with some particular string.
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```
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$ look ecl
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eclectic
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eclectic's
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eclectically
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eclecticism
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eclecticism's
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eclectics
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eclipse
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eclipse's
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eclipsed
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eclipses
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eclipsing
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ecliptic
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ecliptic's
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```
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The look command is generally helpful with spelling and used the /usr/share/dict/words file unless you specify a file name with a command like this one:
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```
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$ look esac .bashrc
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esac
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esac
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esac
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```
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In this case, it acts like grep following by an awk command that prints only the first word on the matching lines.
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### man -k
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The man -k command lists man pages that include the specified word. It basically works like the apropos command.
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```
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$ man -k logrotate
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dh_installlogrotate (1) - install logrotate config files
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logrotate (8) - rotates, compresses, and mails system logs
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logrotate.conf (5) - rotates, compresses, and mails system logs
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```
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### help
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While you may be tempted to use this command when you’re utterly frustrated, what the help command actually does is show you a list of shell built-ins. What’s most surprising is how many of these variables exist. You’re likely to see something like this and then start to wonder what all of these built-ins might do for you:
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```
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$ help
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GNU bash, version 4.4.7(1)-release (i686-pc-linux-gnu)
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These shell commands are defined internally. Type `help' to see this list.
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Type `help name' to find out more about the function `name'.
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Use `info bash' to find out more about the shell in general.
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Use `man -k' or `info' to find out more about commands not in this list.
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A star (*) next to a name means that the command is disabled.
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job_spec [&] history [-c] [-d offset] [n] or hist>
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(( expression )) if COMMANDS; then COMMANDS; [ elif C>
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. filename [arguments] jobs [-lnprs] [jobspec ...] or jobs >
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: kill [-s sigspec | -n signum | -sigs>
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[ arg... ] let arg [arg ...]
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[[ expression ]] local [option] name[=value] ...
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alias [-p] [name[=value] ... ] logout [n]
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bg [job_spec ...] mapfile [-d delim] [-n count] [-O or>
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bind [-lpsvPSVX] [-m keymap] [-f file> popd [-n] [+N | -N]
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break [n] printf [-v var] format [arguments]
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builtin [shell-builtin [arg ...]] pushd [-n] [+N | -N | dir]
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caller [expr] pwd [-LP]
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case WORD in [PATTERN [| PATTERN]...)> read [-ers] [-a array] [-d delim] [->
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cd [-L|[-P [-e]] [-@]] [dir] readarray [-n count] [-O origin] [-s>
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command [-pVv] command [arg ...] readonly [-aAf] [name[=value] ...] o>
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compgen [-abcdefgjksuv] [-o option] [> return [n]
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complete [-abcdefgjksuv] [-pr] [-DE] > select NAME [in WORDS ... ;] do COMM>
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compopt [-o|+o option] [-DE] [name ..> set [-abefhkmnptuvxBCHP] [-o option->
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continue [n] shift [n]
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coproc [NAME] command [redirections] shopt [-pqsu] [-o] [optname ...]
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declare [-aAfFgilnrtux] [-p] [name[=v> source filename [arguments]
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dirs [-clpv] [+N] [-N] suspend [-f]
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disown [-h] [-ar] [jobspec ... | pid > test [expr]
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echo [-neE] [arg ...] time [-p] pipeline
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enable [-a] [-dnps] [-f filename] [na> times
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eval [arg ...] trap [-lp] [[arg] signal_spec ...]
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exec [-cl] [-a name] [command [argume> true
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exit [n] type [-afptP] name [name ...]
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export [-fn] [name[=value] ...] or ex> typeset [-aAfFgilnrtux] [-p] name[=v>
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false ulimit [-SHabcdefiklmnpqrstuvxPT] [l>
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fc [-e ename] [-lnr] [first] [last] o> umask [-p] [-S] [mode]
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fg [job_spec] unalias [-a] name [name ...]
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for NAME [in WORDS ... ] ; do COMMAND> unset [-f] [-v] [-n] [name ...]
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for (( exp1; exp2; exp3 )); do COMMAN> until COMMANDS; do COMMANDS; done
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function name { COMMANDS ; } or name > variables - Names and meanings of so>
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getopts optstring name [arg] wait [-n] [id ...]
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hash [-lr] [-p pathname] [-dt] [name > while COMMANDS; do COMMANDS; done
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help [-dms] [pattern ...] { COMMANDS ; }
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```
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### stat -c
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The stat command displays the vital statistics for a file — its size, owner, group, inode number, permissions, modification and access times. It’s a very useful command that displays more detail than a simple ls -l.
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```
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$ stat .bashrc
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File: .bashrc
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Size: 4048 Blocks: 8 IO Block: 4096 regular file
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Device: 806h/2054d Inode: 421481 Links: 1
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Access: (0644/-rw-r--r--) Uid: ( 1000/ shs) Gid: ( 1000/ shs)
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Access: 2017-08-23 15:13:41.781809933 -0400
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Modify: 2017-06-21 17:37:11.875157790 -0400
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Change: 2017-06-21 17:37:11.899157791 -0400
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Birth: -
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```
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With the -c option, you can specify the fields you want to see. If, for example, you want to see just the file name and access rights for a file or series of files, you might do this:
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```
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$ stat -c '%n %a' .bashrc
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.bashrc 644
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```
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In this command, the %n represents the name of each file, while %a represents the access rights. A %u would be the numeric UID and %U the username.
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```
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$ stat -c '%n %a' bin/*
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bin/loop 700
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bin/move2nohup 700
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bin/nohup.out 600
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bin/show_release 700
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$ stat -c '%n %a %U' bin/*
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bin/loop 700 shs
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bin/move2nohup 700 shs
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bin/nohup.out 600 root
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bin/show_release 700 shs
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```
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### TAB
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If you’re not using the tab command for filename completion, you’re really missing out on a very useful command line trick. The tab command provides filename completion (including directories when you’re using cd). It fills in as much of a name as possible before it hits an ambiguity (more than one file starting with the same letters. If you have a file named bigplans and another named bigplans2017, you’ll hear a sound and have to decide whether to press enter or “2” and tab again to select the second file.
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Join the Network World communities on [Facebook][30] and [LinkedIn][31] to comment on topics that are top of mind.
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--------------------------------------------------------------------------------
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via: https://www.networkworld.com/article/3219684/linux/half-a-dozen-clever-linux-command-line-tricks.html
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作者：[ Sandra Henry-Stocker][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://www.networkworld.com/author/Sandra-Henry_Stocker/
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[1]:https://www.networkworld.com/article/3203369/lan-wan/10-most-important-open-source-networking-projects.html
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[2]:https://www.networkworld.com/article/3203369/lan-wan/10-most-important-open-source-networking-projects.html#tk.nww_nsdr_ndxprmomod
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[3]:https://www.networkworld.com/article/3188295/linux/linux-mint-18-1-mostly-smooth-but-some-sharp-edges.html
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[4]:https://www.networkworld.com/article/3188295/linux/linux-mint-18-1-mostly-smooth-but-some-sharp-edges.html#tk.nww_nsdr_ndxprmomod
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[5]:https://www.networkworld.com/article/3167272/linux/open-source-users-its-time-for-extreme-vetting.html
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[6]:https://www.networkworld.com/article/3167272/linux/open-source-users-its-time-for-extreme-vetting.html#tk.nww_nsdr_ndxprmomod
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[7]:https://www.networkworld.com/article/3218728/linux/how-log-rotation-works-with-logrotate.html
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[8]:https://www.networkworld.com/article/3194830/linux/10-unix-commands-every-mac-and-linux-user-should-know.html
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[9]:https://www.networkworld.com/article/3208389/linux/unix-how-random-is-random.html
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[10]:https://www.networkworld.com/video/51206/solo-drone-has-linux-smarts-gopro-mount
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[11]:https://www.networkworld.com/article/3219826/mobile/prime-members-get-60-off-nucleus-anywhere-intercom-with-amazon-alexa-right-now-deal-alert.html
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[22]:https://www.networkworld.com/article/3218728/linux/how-log-rotation-works-with-logrotate.html
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[23]:https://www.networkworld.com/article/3194830/linux/10-unix-commands-every-mac-and-linux-user-should-know.html
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[24]:https://www.networkworld.com/article/3208389/linux/unix-how-random-is-random.html
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[25]:https://www.networkworld.com/video/51206/solo-drone-has-linux-smarts-gopro-mount
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[26]:https://www.networkworld.com/video/51206/solo-drone-has-linux-smarts-gopro-mount
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[27]:https://www.networkworld.com/article/3219826/mobile/prime-members-get-60-off-nucleus-anywhere-intercom-with-amazon-alexa-right-now-deal-alert.html
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[28]:https://www.networkworld.com/article/3106867/consumer-electronics/32-off-pulse-solo-dimmable-led-light-with-dual-channel-bluetooth-speakers-deal-alert.html
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[29]:https://www.networkworld.com/article/3219685/mobile/57-off-rockbirds-6-pack-led-mini-super-bright-3-mode-tactical-flashlights-deal-alert.html
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[30]:https://www.facebook.com/NetworkWorld/
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