Write a C program that behaves like a shell which displays the command prompt ‘myshell$’. It accepts the command, tokenize the command line and execute it by creating the child process. Also implement the additional command ‘typeline’ as myshell$ typeline n filename: It will display first n lines of the file. myshell$ typeline -n filename: It will display last n lines of the file. myshell$ typeline a filename: It will display all the lines of the file.

SET C

Q.1) Write a C program that behaves like a shell which displays the command prompt ‘myshell$’. It

accepts the command, tokenize the command line and execute it by creating the child process.

Also implement the additional command ‘typeline’ as

myshell$ typeline n filename: It will display first n lines of the file.

myshell$ typeline -n filename: It will display last n lines of the file.

myshell$ typeline a filename: It will display all the lines of the file.

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <unistd.h>
int make_toks(char *s, char *tok[]) {
int i = 0;
char *p;
p = strtok(s, " ");
while(p != NULL) {
tok[i++] = p;
p = strtok(NULL, " ");
}
tok[i] = NULL;
return i;
}
void typeline(char *op, char *fn) {
int fh,
i,
j,
n;
char c;
fh = open(fn, O_RDONLY);
if(fh == -1) {
printf("File %s not found.\n", fn);
return;
}
if(strcmp(op, "a") == 0) {
while(read(fh, &c, 1) > 0)
printf("%c", c);
close(fh);
return;
}
n = atoi(op);
if(n > 0) {
i = 0;
while(read(fh, &c, 1) > 0) {
printf("%c", c);
if(c == '\n') i++;
if(i == n) break;
}
}
if(n < 0) {
i = 0;
while(read(fh, &c, 1) > 0) {
if(c == '\n') i++;
}
lseek(fh, 0, SEEK_SET);
j = 0;
while(read(fh, &c, 1) > 0) {
if(c == '\n') j++;
if(j == i+n+1) break;
}
while(read(fh, &c, 1) > 0) {
printf("%c", c);
}
}
close(fh);
}
int main() {
char buff[80],
*args[10];
while(1) {
printf ("\n");
printf("\nmyshell$ ");
fgets(buff, 80, stdin);
buff[strlen(buff)-1] = '\0';
int n = make_toks(buff, args);
switch (n) {
case 1:
if(strcmp(args[0], "exit") == 0)
exit(1);
if (!fork())
execlp (args [0], args[0], NULL);
break;
case 2:
if (!fork ())
execlp (args [0], args[0], args[1], NULL);
break;
case 3:
if (strcmp(args[0], "typeline") == 0)
typeline (args[1], args[2]);
else {
if (!fork ())
execlp (args [0], args[0], args[1], args[2], NULL);
}
break;
case 4:
if (!fork ())
execlp (args [0], args [0], args [1], args [2], args [3], NULL);
break;
}
}
return 0;
}

Output :

myshell$ typeline a text.txt
pune
kolkata
doremon
mumbai
vadapav
chandigarh
pune
prisonbreak
pogo
misalpav
gogo
pune
\0
myshell$ typeline 3 text.txt
pune
kolkata
doremon
myshell$ typeline -5 text.txt
pogo
misalpav
gogo
pune

\0

<---text.txt-->

pune
kolkata
doremon
mumbai
vadapav
chandigarh
pune
prisonbreak
pogo
misalpav
gogo
pune
\0

Related Question :

Write a C program that behaves like a shell which displays the command prompt ‘myshell$’. It

accepts the command, tokenize the command line and execute it by creating the child process.

Also implement the additional command ‘search’ as

myshell$ search f filename pattern : It will search the first occurrence of pattern in the given

file

myshell$ search a filename pattern : It will search all the occurrence of pattern in the given file

myshell$ search c filename pattern : It will count the number of occurrence of pattern in the

given file

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