aix系统应用基础15 additional shell features

1、course materials may not be reproduced in whole or in part without the prior written permission of ibm.5.04.1 copyright ibm corporation 2008 unit 15additional shell features copyright ibm corporation 2008unit objectivesafter completing this unit, you should be able to: pass positional parameters to

2、shell scriptsuse the test commanduse the if statementimplement interactive shell scriptsimplement loops within scripts copyright ibm corporation 2008$process id (pid)$0shell script name$#number of arguments passed to the shell script$*all command line arguments passed to the script$?exit value of th

3、e last command$!process id of last background processimportant shell variables copyright ibm corporation 2008$0$1$2$3positional parametersparameters can be passed to shell scripts as arguments on the command line: $1, $2, . $9 $10, $11, . $n (korn shell only)$ cat para_scriptecho first parameter ent

4、ered was $1echo second parameter entered was $2echo third parameter entered was $3$ para_script good day sydneyfirst parameter entered was goodsecond parameter entered was daythird parameter entered was sydney copyright ibm corporation 2008highlowprecedencethe expr utilityl use the expr utility to p

5、erform integer arithmetic.l expr offers the following operators: * multiplication / integer division % remainder + addition - subtraction (also unary minus sign) copyright ibm corporation 2008$ var1=6$ var2=3 $ expr $var1 / $var22$ expr $var1 - $var23= use ( ) to group expressions:$ expr ( $var1 + $

6、var2 ) * 545 = use command substitution to store the result in a variable: $ var3=$(expr $var1 / $var2)$ echo $var32expr examples copyright ibm corporation 2008conditional executionthe exit value from a command or group of commands can be used to determine whether to do the next command: command1 &a

7、mp; command2 if (command1 successful) then do (command2) $ ls s* & rm s* command1 | command2 if (command1 not successful) then do (command2) $ cd /dir1 | echo cannot change to /dir1 copyright ibm corporation 2008operator:returns true, if:$string1 = $string2strings are identical$string1 != $strin

8、g2strings are not identical$number1 -eq $number2numbers are equal$number1 -ne $number2numbers are not equal-e $filefile exists-d $filefile is a directory-r $filefile is readable-w $filefile is writabletest commandthe test command allows you to test for a given condition: test expression or expressio

9、n or expression the test command evaluates the expression and returns true or false copyright ibm corporation 2008optional$ cat activeusage=$0 userid if $# -ne 1 then echo proper usage: $usage exit 1 fi if who | grep $1 /dev/null then echo $1 is active else echo $1 is not active fi exit$ cat check_u

10、serusage=$0 username if $# -ne 1 then echo proper usage: $usage exit 2 fi grep $1 /etc/passwd /dev/null if $? -eq 0 then echo $1 is a valid user exit 0 else echo $1 is not a valid user exit 1 fiif commandif condition is truethencarry out this set of actionselsecarry out these alternative actionsfi c

11、opyright ibm corporation 2008if $0 $1 exit -ne -eq $?activity: writing shell scripts copyright ibm corporation 2008read commandthe read command reads one line from standard input and assigns the values of each field to a shell variable.$ cat delfile# usage: delfileecho please enter the file name:rea

12、d nameif -f $name then rm $nameelse echo error: $name is not an ordinary filefi copyright ibm corporation 2008for variable in listdo command(s) done$ cat countfor var in file1 file2 file3do wc -l $vardone $ count 18 file1 20 file2 12 file3$ cat rm_tmpfor file in /tmp/*do echo removing $file rm $file

13、donefor loop syntax copyright ibm corporation 2008while expressiondo command(s)done$ cat informationx=1while $x -lt 9 do echo it is now $(date) echo there are $(ps -e | wc -l) processes running echo there are $(who | wc -l) users logged in x=$(expr $x + 1) sleep 600donewhile loop syntax copyright ib

14、m corporation 2008reserved wordalias built-incommandfunction pathvariablequalifiedpathnamecommand search order copyright ibm corporation 2008path=/bin:/usr/bin:/etc:$home/bin:.ps1=$pwd = env=$home/.kshrcif -s $mail then mailfiecho enter terminal type (default:ibm3151):cread a if -n $a then term=$ael

15、se term=ibm3151fiecho it is now $(date) echo there are $(ps -e | wc -l) processes runningecho there are $(who | wc -l) users logged in export path env term ps1sample .profile copyright ibm corporation 2008checkpoint1. what will the following piece of code do?termtype=$termif $termtype != thenif -f /

16、home/team01/customized_script then /home/team01/customized_scriptelse echo no customized script available !fielseecho you do not have a term variable set !fi2. write a script which will accept two arguments, multiply them together, and display the result. copyright ibm corporation 2008checkpoint sol

17、utions1. what will the following piece of code do?termtype=$termif $termtype != thenif -f /home/team01/customized_script then /home/team01/customized_scriptelse echo no customized script available !fielseecho you do not have a term variable set !fithe script will set a variable termtype to the value

18、 of the term variable. in the if statement the termtype variable will be tested to see if it is not empty. if it is not, then a second check will be carried out to ensure that the /home/team01/customized_script file is an ordinary file. if it is then it will be executed. (for our example we will ass

19、ume that this file contains some extra customized features.) if this file is not an ordinary file, then a message will be sent to the user stating this. if the initial test fails, that is, the termtype variable is empty, then again a message will be sent to the user.2. write a script which will accept two arguments, multiply them together