UNIX操作系统教学课件英文版第十二章.pptVIP

* * School of Software The UNIX Operating System Additional shell programming commands and techniques; Simple application programs Process of developing programs using the shell language. Chapter 12 :Shell Scripts: Writing Application You want to protect the access to your terminal, without logging off and then logging in again. You can write a script to protect your screen. Example lock1: P366 ? 12.1 Writing Application The lock1 Program 12.2 Unix Internals: The Signals (explain in p. 368) Signal Number Name Meaning 1 Hang up Terminal connection is lost. 2[Ctrl-c] [Del] [Break] Interrupt One of the interrupt keys has been pressed. 3[Ctrl-\] Quit One of the quit keys has been pressed 9 Kill The kill –9 command has been issues. 15 terminator The kill command has been issued. 12.2.1 Trapping the Signal: The trap Command Trap “optional command” signal number Trap “echo I refuse to die!” 15 Trap “echo Killed by a signal!” 15 Trap “ ” 15 12.2.2 Resetting the Traps Issuing a trap command in your script changes the default actions of the signals received by your process. Using the trap command, without the optional commands part, changes the specified signals to their default actions. $ trap “ ” 2 3 15 The interrupt, quit, kill commands are ignored. And if any of their keys is pressed, your script keeps on running. If you type the following command: $trap 2 3 15 The specified signals are reset. Interrupt, quit, kill keys are restored, and if any of them is pressed, your running script is terminated. 12.3 tput command $ tput clear clear screen $ tput cup 10 20 put cursor to row 10 column 20 12.4 More Commands 12.4.1 Multiway Branching: the case construct case variable in pattern_1) commands_1;; pattern_2) commands_2;; example p377 menu ……………… ……………… *) default_commands;; esac 12.4.2 R