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Diffstat (limited to '1088/CH24/EX24.9/Example9.sce')
| -rwxr-xr-x | 1088/CH24/EX24.9/Example9.sce | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/1088/CH24/EX24.9/Example9.sce b/1088/CH24/EX24.9/Example9.sce new file mode 100755 index 000000000..38effb613 --- /dev/null +++ b/1088/CH24/EX24.9/Example9.sce @@ -0,0 +1,118 @@ +clear +flag=1 +mode(-1) +clc + +printf("Example 9 : Show the effect of creating a mock child shell which accepts and executes commands \n") +disp("****************************************************************") +disp("Answer : ") +disp("INSTRUCTIONS : ") +halt(' ') +disp("1.These programs are part of systems programming PURELY in Unix and the commands have NO EQUIVALENT IN SCILAB") +halt(' ') +disp("2.However the .c files which are displayed here are also made into a seperate file.If you are a unix user then try compiling and running the programme with gcc or cc compiler") +halt(' ') +disp("3.The outputs displayed here are just MOCK OUTPUTS which are DISPLAYED IN THE TEXTBOOK") +halt(' ') +disp("4.The inconvenience is regretted.") +halt('.............Press [ENTER] to continue.....') +halt("") +clc +printf("\tUNIX SHELL SIMULATOR(DEMO VERSION WITH PRELOADED COMMANDS)\n\n\n") +i=0 +i=i+1;f(i)='/* Program: shell.c -- Accepts user input as a command to be executed. Users the strtok library function for parsing command line*/' +i=i+1;f(i)='#include <stdio.h>' +i=i+1;f(i)='#include <unistd.h>' +i=i+1;f(i)='#include <string.h> /*for strtok*/' +i=i+1;f(i)='#include <wait.h>' +i=i+1;f(i)='' +i=i+1;f(i)='#define BUFSIZE 200 /*Maximum size for the command line */' +i=i+1;f(i)='#define ARGVSIZE 40 /* Maximum number of arguments*/' +i=i+1;f(i)='#define DELIM '+ascii(34)+'\n\t\r'+ascii(34)+' /* White-space delimiters for strtok */' +i=i+1;f(i)='' +i=i+1;f(i)='int main(int argc, char **argv) {' +i=i+1;f(i)=' int i,n ;' +i=i+1;f(i)=' char buf[BUFSIZE + 1]; /* Stores the entered command line */' +i=i+1;f(i)=' char *clargs[ARGVSIZE]; /* Stores the arguments strings */' +i=i+1;f(i)=' int returnval ; /* Used by wait */' +i=i+1;f(i)=' for (;;) { /* Loop forever */' +i=i+1;f(i)=' n = 1;' +i=i+1;f(i)=' write(STDOUT_FILENO, '+ascii(34)+'Shell> '+ascii(34)+',7); /*Display a prompt */' +i=i+1;f(i)=' read(STDIN_FILENO, buf, BUFSIZE); /* Read user input into buf */' +i=i+1;f(i)=' if (!strcmp(buf, '+ascii(34)+'exit\n'+ascii(34)+'))' +i=i+1;f(i)=' exit(0); /* Terminate if user enters exit */' +i=i+1;f(i)=' /* Now parse buf to extract the */' +i=i+1;f(i)=' clargs[0] = strtok(buf, DELIM); /* first word */' +i=i+1;f(i)=' /* Continue parsing until ... */' +i=i+1;f(i)=' while ((clargs[n] = strtok(NULL, DELIM) != NULL)' +i=i+1;f(i)=' n++; /* ...all words are extracted */' +i=i+1;f(i)=' ' +i=i+1;f(i)=' clargs[n] = NULL; /* Set last arguments pointer to NULL */' +i=i+1;f(i)=' switch(fork()) {' +i=i+1;f(i)=' case 0:' +i=i+1;f(i)=' if ((execvp(clargs[0], &clargs[0])) < 0)' +i=i+1;f(i)=' exit(200); /* We will check this value later */' +i=i+1;f(i)=' default: /* Int the parent */' +i=i+1;f(i)=' wait(&returnval); /*After the command has completed.. */' +i=i+1;f(i)=' printf('+ascii(34)+'Exit status of command: %d\n'+ascii(34)+',WEXITSTATUS(returnval));' +i=i+1;f(i)=' for (i=0; i<=n ;i++) /*...initialise both... */' +i=i+1;f(i)=' clargs[i] = '+ascii(34)+'\0'+ascii(34)+'; /*the argument array ...*/' +i=i+1;f(i)=' for (i=0; i<BUFSIZE+1; i++)' +i=i+1;f(i)=' buf[i] = '+ascii(39)+'\0'+ascii(39)+'; /* ... and the buffer that stores command */' +i=i+1;f(i)=' } /* line, so next command can work with */' +i=i+1;f(i)=' } /* an initialized buffer and argument */' +i=i+1;f(i)='} /* array */' +i=i+1;f(i)='' +n=i + + + +printf("\n\n$ cat shell.c # to open the file emp.lst") +halt(' ') +u=mopen('shell.c','wt') +for i=1:n + mfprintf(u,"%s\n",f(i)) + printf("%s\n",f(i)) +end +mclose(u) +halt('') +clc + +halt(' ') + printf("$ cc shell.c") + halt(' ') + printf("$ a.out ") + halt(' ') + printf("Shell> ") + sleep(1500) + printf("grep joker /etc/passwd") + halt(' ') + printf("Exit status of command: 1 #grep returns 1 if pattern not found") + halt(' ') + printf("Shell> ") + sleep(1500) + printf("pwd #Is this the shell builtin? ") +halt(' ') +printf("/users1/home/staff/sumit\nExit status of command: 0") + halt(' ') + printf("Shell> ") +sleep(1500) +printf("ls -lu /usr/bin/pwd # Now check the access time of on-disk pwd") +halt(' ') +printf("-r-xr-xr-x 1 root bin 4360 May 29 01:33 /use/bin/pwd\nExit status of command: 0 # Disk file has just been accessed! ") + halt(' ') + printf("Shell> ") +sleep(1500) +printf("exit") +halt('') +printf("$_ # Back to parent shell") +halt(' ') + +printf("\n\n\n$ exit #To exit the current simulation terminal and return to Scilab console\n\n") +halt("........# (hit [ENTER] for result)") +//clc() + +printf("\n\n\t\t\tBACK TO SCILAB CONSOLE...\nLoading initial environment') +sleep(1000) + + |