Word list prefix filter

filter_wordlist.c

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

bool matches(const char *pre, const char *str) {
    return strncmp(pre, str, strlen(pre)) == 0;
}

int main(int argc, char *argv[]) {
    if (argc < 4) {
        printf("Usage: %s <prefix> <input> <output>", argv[0]);
        return -1;
    }

    char *readFile = argv[2];
    char *writeFile = argv[3];
    FILE *read = fopen(readFile, "r");
    FILE *write = fopen(writeFile, "w");

    if (read == NULL) {
        printf("Cannot open file for reading");
        return -1;
    }

    if (write == NULL) {
        printf("Cannot open file for writing");
        return -1;
    }

    char line[256];
    while (fgets(line, sizeof(line), read)) {
        if (matches(argv[1], line)) {
            fputs(line, write);
        }
    }

    fclose(read);
    fclose(write);

    return 0;
}