Linux & unix shells programing学习笔记

Linux&unix Shells programing学习笔记一、introduction to unix/linux shells1、what is unix ? what is Linux a Little History2、The kernel、The shell、and User4、Unix shellBoume shell 、c shell、kom shell5、Linux shellBash6、Cat /etc/shells(列出系统中所包含的shell)7、Echo $SHELL(列出目前正在使用的shell)8、Cat /etc/passwd(查看用户所对应的shell)9、What is posix?Portable operating system interface of unix10、History of the shell11、Uses of the shellA、when running interactivery, one of the major functions of a shell is interpretcommands entered at the command-line prompt.(交互式下解释命令行输入的命令)B、Another important function of the shell is customize the user‟s environment,normally done in shell initialization files.（定制用户的环境）C、The shell can also be used as an interpreted programming language.（作为解释性的变成语言）12、Responsibilities of the shellThe shell is ultimately responsible for making sure that any commands typed at the prompt get executed properly. Included in those responsibilities are:A、reading input and parsing the command line（读取输入并解析命令行）B、e valuation special characters, such as wildcards and the history character（替换特殊字符）C、s etting up pipes, redirection, and background processing（设置管道、重定向和后台处理）D、handing signals（处理信号）E、setting up programs for execution（程序执行的相关设计）13、System Startup and the login shellA、parsing the command linewhen you type a command at the prompt, the shell read a line of input and parses the command line, breaking the line into words, called tokens. Tokens are separated by spaces and tabs and the command line is terminated by a newline. The shell then checks to see whether the first word is a built-in command or an executable.●History substitution is performed (if applicable).(执行命令替换)●Command line is broken up into tokens, or words.（命令行分解为tokens）●History is update (if applicable).(命令更新)●Quotes are processed.（引入的处理）●Alias substitution and functions are defined (if applicable)（别名替换，和函数的定义）●Redirection , background, and pipes are set up.（设置重定向、后台管理和管道）●Variable substitution( $user, $name, etc.) is performed.（执行变量的替换）●Command substitution (echo “Today is …data‟”) is performed.（执行命令替换）●Filename substitution, called globbing (cat abc.??, rm *.c, etc.) is performed.（执行globbing的文件替换）●Command is executed.（执行命令）B、T ype of commands●Aliases●Keywords●Functions●Built-in commands●Executable programsC、P rocesses and the shell1、what processes are running?●the ps command●the pstree/ptree command2、Whet are system calls?3、Creating processesD、Environment and inheritance1、ownership and permissions2、the file creation mask3、changing permissions and ownership●chmod command●chown command4、the working directory5、variablesE、redirection and pipes1、file descriptors （0：标准输入1：标准输出2：标准错误输出）2、redirection3、pipesF、the shell and signalsA.the signal can be ignoredB.the processes can be stoppedC.the processes can be continuedD.the signal can be caught by a function defined in the program.G、Executing commands from scriptsGo into your favorite editor and type in a set of unix/Linux commands, one per line.Indicate what shell you want by placing the pathname of the shell after the #! On thefirst line.Save your file and turn on the execute permissions so that you can run it.Execute your program just as you would any other unix/Linux command.二、Shell programming Quick Start1、Taking a peek at shell scriptsA.The c shell and TC shell emulate the c language syntax whereas Bourne shell isbased on an older programming language called Algol.B.The bash and korn shells tend to be combination of both the Bourne and C shells,although these shells originated from the Bourne shell2、Sample scripts: Comparing the Major shellsA.Before Getting StartedYou must have a good handle on UNIX/Linux commands. If you do not know the basic commands, you cannot do much with shell programming.B.VI3、The c and TC shell syntax and constructsA、The shbang lineExample: #!/bin/csh or #!/bin/tcshB、C ommentsExample: #This is a comment.C、W ildcardsExample:rm * ; ls ??;cat file[1-3];!!Echo “How are you?”Echo Oh boy\!D、Displaying outputExampleEcho “Hello to you\!”E、Local variablesSet variables_name = valueSet name=”Tom Jones”F、Global variablesSetenv V ARIABLE_NAME valueSetenv PRINTER shakespeareG、Extracting values from variablesEcho $variable_nameEcho $nameEcho $PRINTERH、Reading user inputEcho “what is your name?”Set name = $<I、ArgumentsScriptname arg1 arg2 arg3 …Echo $1 $2 $3Echo $*J、ArraysSet word_list = (word1 word2 word3)Echo $word_list[2]Echo $word_list[1]Echo $word_list or $word_list[*]K、Command substitutioinSet variable_name = `command`Echo $variable_nameL、Arithmetic@n =5+5Echo $nM、OperatorsN、Conditional statementsO、LoopsP、File testing4、The bourne shell syntax and constructsA、the shbang lineB、c ommentsC、w ildcards(通配符)D、displaying outputE、local variablesvariable_name = valueF、global variablesV ARIABLE_NAME=valueExport V ARIABLE_NAMEG、Extracting values from variablesH、Read user inputEcho “what is your name?”Read nameRead name1 name2 …I、Arguments (positional parameters)$scriptname arg1 arg2 arg3 …J、Arrays (positional parameters)Set word1 word2 word3Echo $1 $2 $3K、Command substitutionVariable_name = `command`Echo $variable_nameL、ArithmeticN = `expr 5+5`Echo $nM、Opterators5、The korn shell ConstructsA、the shbang line#!/bin/kshB、c omments#this program will test some filesC、w ildcardsrm *;ls ??;cat file[1-3];echo “How are you?”D、displaying outputecho “who are you?”print “how are you?”E、local variablesvariable_name = valuetypeset variable_name = valuename = “John Doe”F、global variablesexport V ARIABLE_NAME = valueexport PA TH=/bin:/usr/bin;G、extracting values from variablesecho $variable_nameecho $nameH、read user inputprint –n “what is your name?”read nameI、arguments$scriptname arg1 arg2 arg3 …J、arraysset apples pears peachesecho $1 $2 $3K、arithmetictypeset –ivariable_nameL、command substitutionvariable_nae = `command‟variable_name = $(command)echo $variable_nameM、operatorsN、conditional statementsO、loopsP、file testing6、the bash shell constructs三、regular expressions and pattern matching1、definition and examplewhat is a regular expression? A regular expression is just a pattern of characters used to match the same characters in a search.Vim 编辑器：:1,$s/kernel/admin/g (替换文中的kernel为admin，做一个全局替换)撤销操作：按键盘上的u；2、regular expression metacharactersvim 编辑器：:1,$s/\<[Kk]ernel\>/admin/g (替换稳重的K/kernel为admin，做一个全局替换)3、combining regular expression matacharacters四、The grep family1、the meaning of grep●the name grep can be traced back to the editor. If you invoked that editor andwanted to search for a string, you would type at the ex prompt:⏹ /pattern/p●The first line containing the string pattern would be printed as “p”by the printcommand. If you wanted all the lines that contained pattern to be printed, you wouldtype:⏹g/pattern/p●when g precedes pattern, it means “all lines in the file,”or “perform g globalsubstitution.”Because the search pattern is called a regular expression, we cansubstitute RE for pattern and the command reads⏹g/RE/P2、how grep works●the grep command searches for a pattern of characters in a file or multiple files. Ifthe pattern contains whitespace, it must be quoted. The pattern is either a quotedstring or a single word, and all other words following it are treated as filenames.Grep sends its ouput to the screen and does not change or affect the input file inanyway.●FormatGrep word filename filename●Metacharacters3、MetacharactersA metacharacter is a character that represents something other than itself. ^ and $ areexamples of metacharacters.4、Grep and exit statusThe grep command is very useful in shell scripts, because it always returns and exit status to indicate whether it was able to locate the pattern or the file you were looking for.If the pattern is found, grep returns an exit status of 0, indicating success; if grep cannot find the pattern, it returns 1 as its exit status; and if the file cannot be found, grep returns an exit status of 25、Grep with pipesInstead of taking its input from a file, grep often gets its input from a pipeEtc. Ls –l | grep …^d‟6、FgrepThe fgrep command behaves like grep, but does not recognize any regular expression metacharacters as being special. All characters represent only themselves. A caret is simply a caret, a dollar sign is a dollar sign, and so forth.7、Linux and GNU grep8、 Grep –E or egrep五、Sed the streamlined editor1、what is sed?Sed is a streamlined, noninteractive editor. It allows you to perform the same kind of editing tasks used in the vi and ex editors.2、Version of sedLinux uses the GNU version of sed, copyrighted by the free software foundation. This version is almost identical to the sed provided by standard UNIX distributions.Sed –version3、How does sed work?4、Regular expressionsSed, like grep, searches for patterns in files using regular expressions. Regular expressions are patterns of characters enclosed in forward slashes for searches and substitutions.5、Addressing⏹FormatSed …command‟ filename(s)⏹ExampleSed …1,3d‟ myfileSed –n …/[Jj]ohn/p‟ datafile6、Command and options7、 How to modify a file with sedSed is a nondestructive editor. It will display the edits you make on your screen, but it will not change the file you are editing. To really reflect the edits in the file, you must redirect the output to another file, and then rename the orginal fileExample:Sed …1,3d‟ filex > tempMv temp filex8、Error messages and exit statusWhen sed encounters a syntax error, it sends a pretty straightforward error message to standard error, but if it cannot figure out what you did wrong, sed gets “garbled” which we could guess means confused. If the syntax is error-free, the exit status that sed returns to the shell is a zero for success and nonzero integer for failure.9、MetacharactersLike grep, sed supports a number of special metacharacters to control pattern seaching.10、Sed example⏹Printing: the p commandSed …/north/p‟ datafileSed –n …/north/p‟ datafile⏹Deleting: the d commandSed …3d‟ datafileSed –n …3,$d‟ datafileSed …$d‟ datafileSed …/north/d‟ datafile⏹Substitution: the s commandSed …s/west/north/g‟ datafileSed –n …s/^west/north/p‟ datafileSed …s/[0-9][0-9]$/&.5/‟ datafileSed –n …s/hemenway/jones/gp‟ datafileSed –n …s/\(Mar\)got/\1ianne/p‟ datafileSed …s#3#88#g‟ datafile⏹Range fo selected lines: the commaSed –n …/west/,/east/p‟ datafileSed –n …5,/^northeast/p‟ datafileSed …west/,/east/s/$/**/V ACA**/‟ datafile⏹Multiple edits: the e commandSed –e …1,3d‟–e …s/hemenway/jones/‟ datafile⏹Reading from files: the r commandSed …/suan/r newfile‟ datafile⏹Writing to files: the w commandSed –n …/north/w newfile‟ datafile⏹Appending: the a commandSed …^north /a\-→BOOKBOOKE←--… datafile⏹Inserting: the I commandSed …/eastern/i\-→BOOBOOKE←-… datafile⏹Changing: the c commandSed …/eastern/c\ -→ BOOBOOKE←-… datafile⏹Next: the n commandSed …/eastern/{n;s/AM/Archie/;}‟ datafile⏹Transform: the y commandSed …1,3y/asdfgajasdflawehfihaiwehfihasd/ADSFASKDHFLIASFI/‟ datafile⏹Quit: the q commandSed …5q‟ datafileSed …/Lewis/{s/Lewis/Joseph/;q;}‟ datafile⏹Holding and getting: the h and g commandsSed –e …/northeast/h‟–e …$G‟ datafileSed –e …/WE/{h;d;}‟–e …/CT/{G;}‟ datafileSed –e …/northeast/h‟–e …$g‟ datafileSed –e …/WE/{h;d;}‟–e …/CT/{g;}‟ datafile⏹Holding and exchanging: the h and x commandSed –e …/Patricia/h‟–e …/Margot/x‟ datafile11、Sed scripting⏹Sed script examples⏹⏹。