《aix系统应用基础》.ppt

Course materials may not be reproduced in whole or in part without the prior written permission of IBM. 5.0 4.1 Unit 10 Processes Copyright IBM Corporation 2008 Unit Objectives After completing this unit, you should be able to: Define an AIX process Describe the relationship between parent and child processes Create and invoke shell scripts Copyright IBM Corporation 2008 The Process Environment ProgramUser and group ID Data Process ID (PID) Open filesParent Process ID (PPID) Current directoryProgram variables What Is a Process? lEach program runs in a process: lThe variable $ shows the process ID of the current shell: $ echo $ 4712 lThe ps command shows the running processes: $ ps -u team01 Copyright IBM Corporation 2008 login: AIX System PID=202 -ksh login: john Johns Password: xxxxxx $ _ Environment program/usr/bin/ksh uidjohn gidstaff files/dev/tty1 PID202 Login Process Environment Copyright IBM Corporation 2008 AIX System $ cat kfile Environment during execution program/usr/bin/cat uidjohn gidstaff files/dev/tty1 kfile parent -ksh PID310 PPID202 PID=202 -ksh PID=310 cat Process Environment Copyright IBM Corporation 2008 $ echo $ 202 $ ksh (Create a subshell) $ echo $ 206 $ date (Run a command) Tue Jan 4 11:18:26 GMT 2000 $ (Exit the subshell) $ echo $ 202 Subshell PID PPID -ksh 202 1 ksh 206 202 date 208 206 Parents and Children Copyright IBM Corporation 2008 $ x=4 $ ksh $ echo $x $ x=1 $ $ echo $x 4 Subshell Variables and Processes Variables are part of the process environment. Processes cannot access or change variables from another process. Copyright IBM Corporation 2008 variable Shell Subshell export variable=value Activity: Exporting Variables Copyright IBM Corporation 2008 A shell script is a collection of commands stored in a text file $ vi hello echo “Hello, John. Today is: $(date)“ pwd ls :wq $ What Is a Shell Script? Copyright IBM Corporation 2008 $ cat hello echo “Hello, John. Today is: $(date)“(1) pwd(2) ls(3) $ ksh hello Hello, John: Today is: Wed Sep 13 19:34(1) /home/john(2) books letter1 text2sarah (3) $ _ -ksh$ ksh hello ksh script commands Subshell Invoking Shell Scripts (1 of 3) Copyright IBM Corporation 2008 The shell uses the PATH variable to find executable programs. $ cat hello echo “Hello, John. Today is: $(date)“(1) pwd(2) ls(3) $ chmod +x hello $ hello Hello, John: Today is: Wed Sep 13 19:34(1) /home/john(2) books letter1 text2sarah (3) $ _ Subshell Invoking Shell Scripts (2 of 3) Copyright IBM Corporation 2008 $ cat set_dir dir1=/tmp dir2=/usr $ . set_dir $ echo $dir1 /tmp $ echo $dir2 /usr . (dot): Execution in the current shell ? What is the value of dir1 and dir2, if set_dir is called without the dot? Invoking Shell Scripts (3 of 3) Copyright IBM Corporation 2008 Exit Codes from Commands lA command returns an exit value to the parent process: 0 = Success 1 - 255 = Other than successful lThe environment variable $? contains the exit value of the last command: $ cd /etc/security ksh: /etc/security: Permission denied $ echo $? 1 Copyright IBM Corporation 2008 Checkpoint When would you execute a shell script using the dot (.) notation? Why? What is the command that is used to carry down the value of a variable into the subshell? What would be the value of x at the end of the following steps? $ ( . login shell . ) $ ksh $ x=50 $ export x $ $ (what is the value of x set to now?) Copyright IBM Corporation 2008 Checkpoint Solutions When would you execute a shell script using the dot (.) notation? Why? When you are using the script to change variable values in the current shell. What is the command that is used to carry down the value of a variable into the subshell? export variable_name What would be the value of x at the end of the following steps? $ ( . login shell . ) $ ksh $ x=50 $ export x $ $ (what is the value of x set to now?) x would have the value it had before starting the subshell. If the login shell had not set the variable, then after return from the subshell it would still not be set. Copyright IBM Corporation 2008 Shell Scripts Activity: Shell Scripts Copyright IBM Corporation 2008 Unit Summary Shell scripts can be invoked in three ways: $ ksh scriptname(must have read permission) $ scriptname(must have read and execute permission) $ .scriptn