《aix系统应用基础》15 additional shell featu.ppt

Course materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.0 4.1 Unit 15 Additional Shell Features Copyright IBM Corporation 2008 Unit Objectives After completing this unit, you should be able to: Pass positional parameters to shell scripts Use the test command Use the if statement Implement interactive shell scripts Implement 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 the last command $!Process ID of last background process Important Shell Variables Copyright IBM Corporation 2008 $0$1$2$3 Positional Parameters Parameters can be passed to shell scripts as arguments on the command line: $1, $2, . $9 $10, $11, . $n (Korn Shell only) $ cat para_script echo First Parameter entered was $1 echo Second Parameter entered was $2 echo Third Parameter entered was $3 $ para_script Good Day Sydney First Parameter entered was Good Second Parameter entered was Day Third Parameter entered was Sydney Copyright IBM Corporation 2008 high low Precedence The expr Utility l Use the expr utility to perform 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 / $var2 2 $ expr $var1 - $var2 3 = Use ( ) to group expressions: $ expr ( $var1 + $var2 ) * 5 45 = Use command substitution to store the result in a variable: $ var3=$(expr $var1 / $var2) $ echo $var3 2 expr Examples Copyright IBM Corporation 2008 Conditional Execution The exit value from a command or group of commands can be used to determine whether to do the next command: command1 & 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 2008 Operator:Returns true, if: $string1 = $string2Strings are identical $string1 != $string2Strings 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 writable test Command The test command allows you to test for a given condition: test expression or expression or expression The test command evaluates the expression and returns true or false Copyright IBM Corporation 2008 optional $ cat active USAGE=“$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_user USAGE=“$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 fi if Command if condition is true then carry out this set of actions else carry out these alternative actions fi Copyright IBM Corporation 2008 if $0 $1 exit -ne -eq $? Activity: Writing Shell Scripts Copyright IBM Corporation 2008 read Command The read command reads one line from standard input and assigns the values of each field to a shell variable. $ cat delfile # Usage: delfile echo “Please enter the file name:“ read name if -f $name then rm $name else echo “Error: $name is not an ordinary file“ fi Copyright IBM Corporation 2008 for variable in list do command(s) done $ cat count for var in file1 file2 file3 do wc -l $var done $ count 18 file1 20 file2 12 file3 $ cat rm_tmp for FILE in /tmp/* do echo “Removing $file“ rm $FILE done for Loop Syntax Copyright IBM Corporation 2008 while expression do command(s) done $ cat information x=1 while $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 $x + 1) sleep 600 done while Loop Syntax Copyright IBM Corporation 2008 Reserved word alias Built-in command Function PATH variable Qualified pathname Command Search Order Copyright IBM Corporation 2008 PATH=/bin:/usr/bin:/etc:$HOME/bin:. PS1=$PWD = ENV=$HOME/.kshrc if -s “$MAIL“ then mail fi echo “Enter Terminal Type (Default:ibm3151):c“ read a if -n “$a“ then TERM=$a else TERM=ibm3151 fi echo “It is now $(date) “ echo “There are $(ps -e | wc -l) processes running“ echo “There are $(who | wc -l) users logged in“ export PATH ENV TERM PS1 Sample .profile Copyright IBM Corporation 2008 Checkpoint What will the following piece of code do? TERMTYPE=$TERM if $TERMTYPE != “ then if -f /home/team01/customized_script then /home/team01/customized_script else echo No customized script available ! fi else echo You do not have a TERM variable set ! fi Write a script which will accept two arguments, multiply them together, and display the result. Copyright IBM Corporation 2008 Checkpoint Solutions What will the following piece of code do? TERMTYPE=$TERM if $TERMTYPE != “ then if -f /home/team01/customized_script then /home/team01/customized_script else echo No customized script available ! fi else echo You do not have a TERM variable set ! fi The script will set a variable TERMTYPE to the value 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 assume 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. Write a script which will accept two arguments, multiply them together, and display th