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II. Executing Command in a Child Process The first task is to modify the main() function so that a child process is forked and executes the command specified by the user. This will require parsing what the user has entered into separate tokens and storing the tokens in an array of character strings. For example, if the user enters the command ps -ael at the osh> prompt, the values stored in the args array are: args[0] = "ps"| args[1] = "-ael" args[2] = NULL This args array will be passed to the execvpO function, which has the following prototype: execyp(char *command, char “params[]) Here, command represents the command to be performed and params stores the parameters to this command. For this project, the execvp() function should be invoked as execvp(args[0], args). Be sure to check whether the user included & to determine whether or not the parent process is to wait for the child to exit. III. Creating a History Feature The next task is to modify the shell interface program so that it provides a history feature to allow a user to execute the most recent command by entering !!. For example, if a user enters the command Is -1, she can then execute that command again by entering !! at the prompt. Any command executed in this fashion should be echoed on the user's screen, and the command should also be placed in the history buffer as the next command. Your program should also manage basic error handling. If there is no recent command in the history, entering !! should result in a message “No commands in history."

II. Executing Command in a Child Process The first task is to modify the main() function so that a child process is forked and executes the command specified by the user. This will require parsing what the user has entered into separate tokens and storing the tokens in an array of character strings. For example, if the user enters the command ps -ael at the osh> prompt, the values stored in the args array are: args[0] = "ps"| args[1] = "-ael" args[2] = NULL This args array will be passed to the execvpO function, which has the following prototype: execyp(char *command, char “params[]) Here, command represents the command to be performed and params stores the parameters to this command. For this project, the execvp() function should be invoked as execvp(args[0], args). Be sure to check whether the user included & to determine whether or not the parent process is to wait for the child to exit. III. Creating a History Feature The next task is to modify the shell interface program so that it provides a history feature to allow a user to execute the most recent command by entering !!. For example, if a user enters the command Is -1, she can then execute that command again by entering !! at the prompt. Any command executed in this fashion should be echoed on the user's screen, and the command should also be placed in the history buffer as the next command. Your program should also manage basic error handling. If there is no recent command in the history, entering !! should result in a message “No commands in history."

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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i need answer of II and III please

 

II. Executing Command in a Child Process The first task is to modify the main() function so that a child process is forked and executes the command specified by the user. This will require parsing what the user has entered into separate tokens and storing the tokens in an array of character strings. For example, if the user enters the command ps -ael at the osh> prompt, the values stored in the args array are: args[0] = "ps" args[1] = "-ael" args[2] = NULL This args array will be passed to the execvp() function, which has the following prototype: execyp(char *command, char *params[]) Here, command represents the command to be performed and params stores the parameters to this command. For this project, the execvp() function should be invoked as execvp(args[0], args). Be sure to check whether the user included & to determine whether or not the parent process is to wait for the child to exit. III. Creating a History Feature The next task is to modify the shell interface program so that it provides a history feature to allow a user to execute the most recent command by entering !!. For example, if a user enters the command Is -1, she can then execute that command again by entering !! at the prompt. Any command executed in this fashion should be echoed on the user's screen, and the command should also be placed in the history buffer as the next command. Your program should also manage basic error handling. If there is no recent command in the history, entering !! should result in a message “No commands in history."
Transcribed Image Text:II. Executing Command in a Child Process The first task is to modify the main() function so that a child process is forked and executes the command specified by the user. This will require parsing what the user has entered into separate tokens and storing the tokens in an array of character strings. For example, if the user enters the command ps -ael at the osh> prompt, the values stored in the args array are: args[0] = "ps" args[1] = "-ael" args[2] = NULL This args array will be passed to the execvp() function, which has the following prototype: execyp(char *command, char *params[]) Here, command represents the command to be performed and params stores the parameters to this command. For this project, the execvp() function should be invoked as execvp(args[0], args). Be sure to check whether the user included & to determine whether or not the parent process is to wait for the child to exit. III. Creating a History Feature The next task is to modify the shell interface program so that it provides a history feature to allow a user to execute the most recent command by entering !!. For example, if a user enters the command Is -1, she can then execute that command again by entering !! at the prompt. Any command executed in this fashion should be echoed on the user's screen, and the command should also be placed in the history buffer as the next command. Your program should also manage basic error handling. If there is no recent command in the history, entering !! should result in a message “No commands in history."
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