pwd:print work directory 打印当前目录 显示出当前工作目录的绝对路径
	ps: process status(进程状态，类似于windows的任务管理器)
	常用参数：－auxf
	 ps -auxf 显示进程状态
	 df: disk free 其功能是显示磁盘可用空间数目信息及空间结点信息。换句话说，就是报告在任何安装的设备或目录中，还剩多少自由的空间。
	du: Disk usage
	rpm：即RedHat Package Management，是RedHat的发明之一
	rmdir：Remove Directory（删除目录）
	rm：Remove（删除目录或文件）
	cat: concatenate 连锁
	cat file1file2>>file3 把文件1和文件2的内容联合起来放到file3中
	 insmod: install module,载入模块
	ln -s : link -soft 创建一个软链接，相当于创建一个快捷方式
	mkdir：Make Directory(创建目录)
	touch
	man: Manual
	su：Swith user(切换用户)
	cd：Change directory
	ls：List files
	ps：Process Status
	mkdir：Make directory
	rmdir：Remove directory
	mkfs: Make file system
	fsck：File system check
	uname: Unix name
	lsmod: List modules
	mv: Move file
	rm: Remove file
	cp: Copy file
	ln: Link files
	fg: Foreground
	bg: Background
	chown: Change owner
	chgrp: Change group
	chmod: Change mode
	umount: Unmount
	dd: 本来应根据其功能描述“Convert an copy”命名为“cc”，但“cc”已经被用以代表“CComplier”，所以命名为“dd”
	tar：Tape archive （磁带档案）
	ldd：List dynamic dependencies
	insmod：Install module
	rmmod：Remove module
	lsmod：List module
	文件结尾的"rc"（如.bashrc、.xinitrc等）：Resource configuration
	Knnxxx /Snnxxx（位于rcx.d目录下）：K（Kill）；S(Service)；
	nn（执行顺序号）；xxx（服务标识）
	.a（扩展名a）：Archive，static library
	.so（扩展名so）：Shared object，dynamically linked library
	.o（扩展名o）：Object file，complied result of C/C++ source file
	RPM：Red hat package manager
	dpkg：Debian package manager
	apt：Advanced package tool（Debian或基于Debian的发行版中提供）
	部分Linux命令缩写
	bin = Binaries (二进制文件)
	/dev = Devices (设备)
	/etc = Etcetera (等等)
	/lib = LIBrary
	/proc = Processes
	/sbin = Superuser Binaries (超级用户的二进制文件)
	/tmp = Temporary (临时)
	/usr = Unix Shared Resources
	/var = Variable (变量)
	FIFO = First In, First Out
	GRUB = GRand Unified Bootloader
	IFS= Internal Field Seperators
	LILO = LInux LOader
	MySQL = My 是最初作者女儿的名字，
	SQL = Structured QueryLanguage
	PHP = Personal Home Page Tools = PHP HypertextPreprocessor
	PS = Prompt String
	Perl = "Pratical Extraction and Report Language"(实际的抽取和报告语言) ="Pathologically Eclectic Rubbish Lister"
	Python 得名于电视剧Monty Python's Flying Circus
	Tcl = Tool Command Language
	Tk = ToolKit
	VT = Video Terminal
	YaST = Yet Another Setup Tool
	apache = "a patchy" server
	apt = Advanced Packaging Tool
	ar = archiver
	as = assembler
	awk = "Aho Weiberger and Kernighan"三个作者的姓的第一个字母
	bash = Bourne Again SHell
	bc = Basic (Better) Calculator
	bg = BackGround
	biff = 作者HeidiStettner在U.C.Berkely养的一条狗,喜欢对邮递员汪汪叫。
	cal = Calendar (日历)
	cat = Catenate (链接)
	cd = Change Directory
	chgrp = Change Group
	chmod = Change Mode
	chown = Change Owner
	chsh = Change Shell
	cmp = compare
	cobra = Common Object Request BrokerArchitecture
	comm = common
	cp = Copy
	cpio = CoPy In and Out
	cpp = C Pre Processor
	cron = Chronos 希腊文时间
	cups = Common Unix Printing System
	cvs = Current Version System
	daemon = Disk And Execution MONitor
	dc = Desk Calculator
	dd = Disk Dump (磁盘转储)
	df = Disk Free
	diff = Difference
	dmesg = diagnostic message
	du = Disk Usage
	ed = editor
	egrep = Extended GREP
	elf = Extensible Linking Format
	elm = ELectronic Mail
	emacs = Editor MACroS
	eval = EVALuate
	ex = EXtended
	exec = EXECute (执行)
	fd = file descriptors
	fg = ForeGround
	fgrep = Fixed GREP
	fmt = format
	fsck = File System ChecK
	fstab = FileSystem TABle
	fvwm = F*** Virtual Window Manager
	gawk = GNU AWK
	gpg = GNU Privacy Guard
	groff = GNU troff
	hal = Hardware Abstraction Layer
	joe = Joe's Own Editor
	ksh = Korn SHell
	lame = Lame Ain't an MP3 Encoder
	lex = LEXical analyser
	lisp = LISt Processing = Lots of IrritatingSuperfluous Parentheses
	ln = Link
	lpr = Line PRint
	ls = list
	lsof = LiSt Open Files
	m4 = Macro processor Version 4
	man = MANual pages
	mawk = Mike Brennan's AWK
	mc = Midnight Commander
	mkfs = MaKe FileSystem
	mknod = Make Node
	motd = Message of The Day
	mozilla = MOsaic GodZILLa
	mtab = Mount TABle
	mv = Move
	nano = Nano's ANOther editor
	nawk = New AWK
	nl = Number of Lines
	nm = names
	nohup = No HangUP
	nroff = New ROFF
	od = Octal Dump
	passwd = Passwd
	pg = pager
	pico = PIne's message COmposition editor
	pine = "Program for Internet News &Email" = "Pine is not Elm"
	ping = 拟声 又 = Packet Internet Grouper
	pirntcap = PRINTer CAPability
	popd = POP Directory
	pr = pre
	printf = Print Formatted
	ps = Processes Status
	pty = pseudo tty
	pushd = PUSH Directory
	pwd = Print Working Directory
	rc = runcom = run command, rc还是plan9的shell
	rev = REVerse
	rm = ReMove
	rn = Read News
	roff = RunOFF
	rpm = RPM Package Manager = RedHat PackageManager
	rsh, rlogin, rvim中的
	r = Remote
	rxvt = ouR XVT
	seamoneky = 我
	sed = Stream Editor
	seq = SEQuence
	shar = Shell ARchive
	slrn = S-Lang rn
	ssh = Secure Shell
	ssl = Secure Sockets Layer
	stty = Set TTY
	su = Substitute User
	svn = SubVersion
	tar = Tape ARchive
	tcsh = TENEX C shell
	tee = T (T形水管接口)
	telnet = TEminaL over Network
	termcap = terminal capability
	terminfo = terminal information
	tex = τ?χνη的缩写，希腊文art
	tr = traslate
	troff = Typesetter new ROFF
	tsort = Topological SORT
	tty = TeleTypewriter
	twm = Tom's Window Manager
	tz = TimeZone
	udev = Userspace DEV
	ulimit = User's LIMIT
	umask = User's MASK
	uniq = UNIQue
	i = VIsual = Very Inconvenient
	vim = Vi IMproved
	wall = write all
	wc = Word Count
	wine = WINE Is Not an Emulator
	xargs = eXtended ARGuments
	xdm = X Display Manager
	xlfd = X Logical Font Description
	xmms = X Multimedia System
	xrdb = X Resources DataBase
	xwd = X Window Dump
	yacc = yet another compiler compiler
	Fish = the Friendly Interactive SHell
	su = Switch User
	MIME = Multipurpose Internet Mail Extensions
	ECMA = European Computer ManufacturersAssociation

将字符进行替换压缩和删除,tr命令 可以对来自标准输入的字符进行替换、压缩和删除。它可以将一组字符变成另一组字符，经常用来编写优美的单行命令，作用很强大。

命令语法

tr [选项] [字符串1] [字符串2]

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tr命令用于替换和删除文件中的字符，也可以对字符串进行替换和删除。

语法格式：tr 参数 字符串或文件

使用tr命令对字符串或者文件中的内容进行大小写转换：

<小于号在Linux系统是输出重定向，并不会改变文件里的内容，如图1命令1，文件里面的数据并没有改变，如果要同时改变文件里的内容，则需要使用 >大于号，重定向写入到文件。

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Linux tr 命令用于转换或删除文件中的字符。

tr 指令从标准输入设备读取数据，经过字符串转译后，将结果输出到标准输出设备。

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