Simulation of Unix Commands - grep

SIMULATION OF UNIX COMMANDS

Programs

// 3. Grep command

#include <stdio.h>                 

#include <stdlib.h>

int substr( char *line, char *pat);

int main(int argc, char *argv[])

{

        FILE *fp;

        char line[128];

        if ( argc == 2 )

                fp = stdin;

        else if ( argc == 3 )

        {

                fp = fopen(argv[2], "r");

                if ( fp == NULL )

                        printf("file %s cannot be opened \n", argv[1]);

        }

        else

        {

                printf("Usage: %s <pattern> <file> \n", argv[0]);

                exit(1);

        }

        while( fgets(line, sizeof(line), fp) )

                if ( substr(line, argv[1]) )

                        printf("%s",line);

        fclose (fp);

        return 0;

}

int substr( char *line, char *pat)

{

        int i,j,k;

        for( i=0; line[i] != '\0'; i++)

                for( j=i,k=0; line[j]==pat[k] && pat[k] != '\0'; j++,k++);

                             if ( pat[k] == '\0')

                                      return 1;

        return 0;

}