Simulation of Unix Commands 3

SIMULATION OF UNIX COMMANDS – grep command

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// 3. Grep command

#include <stdio.h>

#include <stdlib.h>

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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;

}

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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;

}