Basically simplified example from getline(2) man page with optional stdin vs file reading

minicat.c

#include <stdio.h>
#include <stdlib.h>

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

    FILE *stream;
    char *line = NULL;
    size_t len = 0;
    ssize_t nread;
    
    stream = stdin;
    if (argc == 2)
        stream = fopen(argv[1],"r");
    
    //while( (getline(&line,0,stream)) != -1 )
    //    printf("Line:%s\n",&line);
    while( (getline(&line,&len,stream)) != -1 )
        printf("%s",line);
    
    free(line);
    fclose(stream);    
    return 0;
}