include <stdio.h>
 
int main(int argc, char *argv[])
{
    int x;
 
    printf("%d\n",argc);
    for (x=0; x<argc; x++)
        printf("%s\n",argv[x]);
    return 0;
}

#include <stdio.h>
#include    <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include    <string.h>
void oops(char *s1, char *s2);
main(int argc, char *argv[] )
{   
 int write_fd, nwrite;    
char buffer[100];    
char *location;   
 int length=strlen(argv[1]);    
if(argc != 4)
{ //check that the arguments are given correctly.        
printf("Error: Too many arguments!\nFilename should have no spaces.\n\nUsage: %s string1 string2 filename\n",argv[0]);        
exit(1);    
}    
if(strlen(argv[1])!=strlen(argv[2]))
{ //check whether the initial and replacement strings are of same size.        
printf("Error: string 1 must be of equal length to string \n");        
exit(1);    
}    
printf("Input text and press enter:\n");    
gets(buffer); 
//put text from stdin into string buffer    
printf("Replacing all occurances of \"%s\" with \"%s\" in \"s\"\n",argv[1],argv[2],buffer);   
 while(location=strstr(buffer,argv[1])) 
//replace all string1's with string2's in buffer  
  {        strncpy(location,argv[2],length);   
 }  
  /*write to file*/    
printf("Writing to file... \n");   
 if ( (write_fd=creat( argv[3], O_WRONLY)) == -1 )    
 oops( "Cannot create file", argv[3]); 
if ( write( write_fd, buffer, strlen(buffer) ) != strlen(buffer) )    
 oops("Write error to ", argv[3]); /* close file */ 
if (close(write_fd) == -1 ) 
oops("Error closing files","");    
printf("Done.\nResult:");    printf("%s\n",buffer); //output result}
void oops(char *s1, char *s2){ fprintf(stderr,"Error: %s ", s1); perror(s2); exit(1);}