《aix系统应用基础》15 additional shell featu

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5
expr Examples
$ var1=6 $ var2=3 $ expr $var1 / $var2 2
$ expr $var1 - $var2 3
=> Use \( \) to group expressions:
$ expr \( $var1 + $var2 \) \* 5 45
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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)
Third Parameter entered was Sydney
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4
The expr Utility
Use the expr utility to perform integer arithmetic.
expr offers the following operators:
\* multiplication / integer division % remainder + addition - subtraction (also unary minus sign)
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2
Important Shell Variables
$$ Process ID (PID) $0 Shell 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
=> Use command substitution to store the result in a variable:
$ var3=$(expr $var1 / $var2) $ echo $var3 2
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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
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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
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
Unit 15 Additional Shell Features
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Course materials may not be reproduced in whole or in part without the prior written permission of IBM.
5.0
4.1
Unit Objectives
$number1 -ne $number2 Numbers are not equal
-e $file
File exists
-d $file
File is a directory
-r $file
File is readable
-w $file
File is writable
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8
if Command
Operator:
Returns true, if:
$string1 = $string2
Strings are identical
$string1 != $string2
Strings are not identical
$number1 -eq $number2 Numbers are equal
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
if condition is true then
carry out this set of actions else
carry out these alternative actions fi
} optional
$ cat actห้องสมุดไป่ตู้ve
USAGE="$0 userid"
$ cat check_user
$ cat para_script echo First Parameter entered was $1 echo Second Parameter entered was $2 echo Third Parameter entered was $3
$0
$1 $2 $3
$ para_script Good Day Sydney First Parameter entered was Good Second Parameter entered was Day