C : bash event not found

Question

Hello so i don't have any friends who could help me i get this eror when i test this code look what i have already done

./main "Hello World!" "ld"
-bash: !": event not found

what is this what is happening

here is the main :

#include <stdio.h>
#include <err.h>
#include <string.h>
int main (int argc, char *argv[]) 
{

int p = 0;
int q = 1;
int place = 0;
int check = 0;
char position[10] = ""; // i think the error is here

while (argv[1][p] != '\0')
{
    if (argv[1][p] == argv[2][0])
    {
        place = p;
        while (argv[2][q] != '\0' && argv[1][p + q] != '\0' && argv[2][q] == argv[1][p + q])
            { 
            q += 1;
            }
        if (argv[2][q] == '\0')
        {
            check = 1;
            printf("%s\n", argv[1]); //i think the error is here
            for (int n = 0; n < place; n += 1) //i think the error is here
            {
                strcat(position, " "); //i think the error is here
            }
            strcat(position, "^"); //i think the error is here
            printf("%s\n", position); //i think the error is here

        }
    }
    p += 1;
}
if (check == 0)
{
    printf("Not found!\n");
}

return 0 ; // return 0
}

I added comment so you can maybe help

and also how can I create

char position[10] = "";

without giving the length I tried

char position[] = "";

but it doesn't compile

Answer 1

Short Answer

With exclamation points, use single quotes.

./main 'Hello World!' 'ld'

Long Answer

The exclamation mark does something funny in Bash. Read more... unix.stackexchange.

The exclamation mark is part of history expansion in bash. To use it you need it enclosed in single quotes.

Even trying !" with echo gives

$ echo "Hello World!"
-bash: !: event not found

You could use double quotes, but you may need a blackslash.

Note that in double quotes, a backslash before the exclam prevents history expansion, BUT the backslash is not removed in such a case.

So ./main "Hello World\!" "ld" would also work, but you might need to account for the blackslash within your C/C++.

Note that the behaviour of the exclamation point may have changed. Executing echo "Hello World!" make work on some bash versions. Credits to Benjamin W.

Answer 2

I think that the "!" maybe causing some problems with your bash shell. I ran it in mine without any problems. If you try my code and it fails, try running it as

./main "Hello World" ld

The logic in your code is confusing because you are trying to use the argv[1] and argv[2] inputs directly. it can be done, but the way that it is written is very difficult to follow.

I have reduced the complexity of the code by renaming the variables so that you can follow the logic more easily.

I also add a sub-routine to carry out the string compare. Of course, there is a library strcmp() function, I am not sure if you avoided that function because of some requirement. You could modify this to use the std strcmp().

Good code should be documented by the names of the variables. Here is what I came up with:

#include <stdio.h>
#include <string.h>

/* compare two c strings.  Return 0 if equivalent. Return -1 if not.
 * Assumes that the strings are terminated with a '\0' character */
int homegrown_strcmp(char* str1, char* str2) {

    while( *str2 != '\0') {
        if(*str1 != *str2)
            return -1;
        str1++;
        str2++;
    }
    return 0;

}

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


    char* haystack = argv[1]; /* This is the string we are searching inside */
    char* needle = argv[2]; /* This is what we are looking for */

    char* poker = haystack;  /* We will use this to poke into our haystack until
 * we find our needle or fail */

    unsigned int position = 0;
    while(*poker != '\0') {
        if(homegrown_strcmp(poker, needle) == 0) {
            printf("Found at position %u\n", position);
            return 0;
        }
        poker++;
        position++;
    }
    printf("Not found\n");
    return -1;
}