C system() function-CodePudding

I'm trying to create a file in linux and give it executable rights using system() function in a C program. Here is the code:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main(int argc, char *argv[], char *envp[]){
char s[100];
strcpy(s, "touch ");
strcpy(s, argv[1]);
strcpy(s, "; chmod a x ");
strcpy(s, argv[1]);
system(s);
return 0;
}

But when I call compiled file with argument "abs" for example (consider I want "abs" as the name of the file to be created) it gives such output:

sh: 1: abs: not found

How can it be fixed? It's important that I have to use C programming and system() function.

CodePudding user response：

It seems that answer is not understandable for future readers, let me try to explain what is the difference between strcpy and strcat

strcpy() copies one string into another.
strcat() function concatenates string by appending source string to destination string.

In the original code, every time a "strcpy" function was called, a previous value in the buffer was overridden.

char s[100];
strcpy(s, "touch "); // s = touch
strcpy(s, argv[1]); // s = abc (argv[1] value)
strcpy(s, "; chmod a x "); // s = ; chmod a x 
strcpy(s, argv[1]); // s = abc (argv[1] value)
system(s); // execute s = abc

And finally, since "s" is "abc" system() function tries to execute it, which is producing the following error:

sh: 1: abs: not found

In the modified version, instead of overwriting the previous value, the new value is appended to the buffer.

char s[100];
strcpy(s, "touch "); // s = touch
strcat(s, argv[1]); // s = touch abc
strcat(s, "; chmod a x "); // s = touch abc; chmod a x
strcat(s, argv[1]); // s = touch abc; chmod a x abc
system(s); // execute s = touch abc; chmod a x abc

CodePudding user response：

The code should be changed to the following:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main(int argc, char *argv[], char *envp[]){
char s[100];
strcpy(s, "touch "); //s = "touch "
strcat(s, argv[1]); //s = "touch "   argv[1]
strcat(s, "; chmod a x "); //s = "touch "   argv[1]   "; chmod a x " 
strcat(s, argv[1]); //s =  "touch "   argv[1]   "; chmod a x "   argv[1]
system(s); //system("touch "   argv[1]   "; chmod a x "   argv[1])
return 0;
}

Thanks a lot to commentators!