《aix系统应用基础》08 shell ba.ppt

Course materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.0 4.1 Unit 8 Shell Basics Copyright IBM Corporation 2008 Unit Objectives After completing this unit, you should be able to: Use wildcards to access files with similar names Use redirection and pipes to control the input and output of processes Use line continuation to enter commands that span the command line Group commands in order to control their execution Copyright IBM Corporation 2008 The Shell lKorn (ksh) or Bourne (bsh) or C (csh) lUser interface to AIX lCommand interpreter lEnables multiple tasks lComprehensive programming language Copyright IBM Corporation 2008 Metacharacters and Wildcards lMetacharacters are characters that the shell interprets as having a special meaning. Examples: | ; ! * ? $ “ lWildcards are a subset of metacharacters that are used to search for and match file patterns. Examples: * ? ! - Copyright IBM Corporation 2008 / home team01 test1 test1.2 test1.3 myfile ne net new nest few File Name Substitution (1 of 2) Wildcards: *? One character compare: $ ls ne? net new $ rm ?e? few net new Multiple character compare: $ cp n* /tmp ne net new nest $ qprt *w new few $ echo test1* test1 test1.2 test1.3 Copyright IBM Corporation 2008 Inclusive Lists: ! - $ ls nestw net new $ rm fghjdnetw few net new $ ls *1-5 test1 test1.2 test1.3 $ qprt !tn* myfile few $ cat ?!y*2-5 test1.2 test1.3 / home team01 test1 test1.2 test1.3 myfile ne net new nest few File Name Substitution (2 of 2) Copyright IBM Corporation 2008 standard in (0) standard error (2)standard out (1) cmd The Standard Files Copyright IBM Corporation 2008 Standard in:1 Standard error:22 File Descriptors Three descriptors are assigned by the shell when the program starts: Copyright IBM Corporation 2008 Input Redirection lDefault standard input $ mail team01 Subject: Letter This is a letter. Cc: $ lRedirect input from a file: $ ls ls.out $ lRedirecting and appending output to a file: $ who whos.there $ Copyright IBM Corporation 2008 Creating a File with cat lWhile normally used to list the contents of files, using cat with redirection can be used to create a file: $ ls letter acctfile file1 $ cat file1 This is a test file. The file has 2 lines. $ lUsing redirection: $ cat newfile This is line 1 of the file. This is the 2nd line. And the last. $ ls letter acctfile file1 newfile Copyright IBM Corporation 2008 Activity: Review Shell Basics 1 Which files are listed when the following commands are executed? $ ls /home/team01/*.? $ ls /tmp/a-zA-Z*.0-9 2 True or False: The command “ls *“ lists all files in a directory. 3 Write down the file descriptors for the following command: $ wc -l /tmp/lines Standard input: Standard output: Standard error: 4 You want to append file testfile1 to file report99. Which command is correct? ocat report99 report99 ocat testfile1 report99 ocat testfile1 report99 Copyright IBM Corporation 2008 Error Redirection lDefault standard error: $ cat filea fileb This is output from filea. cat: cannot open fileb lRedirecting error output to a file: 2 (To append: 2) $ cat filea fileb 2 errfile This is output from filea $ cat errfile cat: cannot open fileb $ cat filea fileb 2 /dev/null This is output from filea Copyright IBM Corporation 2008 Combined Redirection lCombined redirects: $ command outfile 2 errfile appendfile 2 errfile outfile 2“: $ ls -R outfile ; exit is equivalent to entering: $ ls -R outfile $ exit Copyright IBM Corporation 2008 Line Continuation The backslash () followed by a new line character can be used to continue a command on a separate line. A secondary prompt character “ is issued by the shell to indicate line continuation. $ cat /home/mydir/mysubdir/mydata /home/yourdir/yoursubdir/yourdata Copyright IBM Corporation 2008 Checkpoint (1 of 2) What will the following command match? $ ls ?!a-z*0-9t For questions 2-4, indicate where the standard input, standard output and standard error will go. $ cat file1 standard input (0): standard output (1): standard error (2): $ mail tim newprofile 21 standard input (0): standard output (1): standard error (2): For questions 5, 6, and 7, create command lines to display the content of filea using cat and then perform the following: Place the output of the command in fileb and the errors in filec. Place the output of the command in fileb and associate any errors with the output in fileb. Place the output in fileb and discard any error messages. (Do not display or store error messages.) Copyright IBM Corporation 2008 Checkpoint Solutions (2 of 2) $ cat .profile newprofile 21 standard input (0): keyboard standard output (1): newprofile standard error (2): a file named 1 For questions 5, 6, and 7, create command lines to display the content of filea using cat and then perform the following: Place the output of the command in fileb and the errors in filec. $ cat filea fileb 2 filec Place the output of the command in fileb and associate any errors with the output in fileb. $ cat filea fileb 2&1 Place the output in fileb and discard any error messages. (Do not display or store error messages.) $ cat filea fileb 2 /dev/null Copyright IBM Corporation 2008 Exercise: Shell Basics Copyright IBM Corporation 2008 Unit Summary Wildcards, * and ?, provide a convenient way for specifying multiple files or directory names. The wildcard notation is like using the ? but it allows you to choose specific characters to be matched. Three files automatically opened for redirection are standard in, standard out, and standard error. I/O redirection alters the default input source or output desti