«Ненормальное» сравнение переменной shn с единицей.

#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/stat.h> 
#include <sys/types.h>
#include <string.h>
#include <ctype.h>
#define _GNU_SOURCE
#include <getopt.h>
void itoa(register unsigned long n, register char s[]);
void dchk(int f);
int ferr();
int usage();
int main(int argc, char** argv){
    register int ch;
    int longIndex;
    register short sht, shn, shcc, num;
    static const struct option longOpts[] = {
    { "show-nonprinting", no_argument, NULL, 'v' },
    { "show-tabs", no_argument, NULL, 'T' },
    { "show-ends", no_argument, NULL, 'E' },
    { "show-all", no_argument, NULL, 'A' },
    { "number", no_argument, NULL, 'n' },
    { "version", no_argument, NULL, 0 },
    { NULL, no_argument, NULL, 0 }
    };
    while((ch=getopt_long(argc, argv, "ETAethun",longOpts,&longIndex))!= -1){
        switch (ch) {
                case 'n':
                    num = 1;
                    break;
                case 'E':
                    shn = 1;
                    break;
                case 'T':
                    sht=1;
                    break;
                case 'A':{
                    shn=1;
                    sht=1;
                    shcc=1;
                    break;
                    }
                case 'v':
                    shcc=1;
                    break;
                case 'e':{
                    shcc=1;
                    shn=1;
                    break;
                    }
                case 't':{
                    shcc=1;
                    sht=1;
                    break;
                    }
                case '?':
                case 'h':
                    usage();
                case 'u':
                    break;
                case 0:if(strcmp( "version",longOpts[longIndex].name)==0){
                    write(1,"sysccat version 0.1\n",20);
                    _exit(0);
                    }
                    else usage();
                }
        }
    argv+=optind;
    argc-=optind;
    if(argc==0)usage();
    if(!sht&&!shn&&!shcc&&!num)for(int x=0;x<argc;++x){
        int fd=open(argv[x],O_RDONLY);
        if(fd<0)ferr();
        dchk(fd);
        char a;
        while(read(fd,&a,1)>0)write(0,&a,1);
        close(fd);
    }
        else for(int x=0;x<argc;++x){
            int fd=open(argv[x],O_RDONLY);
            if(fd<0)ferr();
            dchk(fd);
            if(num)write(0,"1: ",3);
            register int i=1;
            char a;
            while(read(fd,&a,1)>0){
                if(num&&a=='\n'){
                                if(read(fd,&a,1)==0){
                                                    if(shn)write(0,"$",1);
                                                    write(0,&a,1);
                                                    }
                                else{
                                    if(shn)write(0,"$",1);
                                    write(0,"\n",1);
                                    char b[11];
                                    ++i;
                                    itoa(i,b);
                                    write(0,&b,strlen(b));
                                    write(0,": ",2);
                                    lseek(fd, -1, SEEK_CUR);
                                    }
                }
                else if(sht&&a=='\t')write(1,"^I",2);
                    else if((shn==1)&&a=='\n')write(1,"$\n",2);
                        else if(shcc&&iscntrl(a)&&a!='\n'&&a!='\t'){
                                                                    char c=a+64;
                                                                    write(1,"^",1);
                                                                    write(1,&c,1);
                                                                    }
                            else write(1,&a,1);
        }
        close(fd);
    }
    _exit(0);
}
int usage(){
    write(1,"Usage: sysccat [OPTIONS]... [FILE]...\n"
    "-h or --help Displays this info and exit.\n"
    "-n or --number Numbers the output strings.\n"
    "--version Displays version and exit.\n"
    "-v or --show-nonprinting Displays non-printing(control) characters, except for tabulation and carriage return/end-of-line symbols.\n"
    "-A, -vET or --show-all Displays all control characters.\n"
    "-t or -vT Displays all control characters, except for carriage return/end-of-line symbol.\n"
    "-u Ignored; for POSIX compatibility.\n"
    "-e or -vE Displays all control characters, except for tabulation symbol.\n",547);
    _exit(0);
    }
void itoa(register unsigned long n, register char s[]){
     register short i,j;
     register char c;
     i=0;
     do{
         s[i++] = n % 10 + '0';
     }while((n/=10)>0);
     s[i]='\0';
     for(i=0,j=strlen(s)-1;i<j;i++,j--){
         c = s[i];
         s[i] = s[j];
         s[j] = c;
     }
 }
int ferr(){
    switch(errno){
        case ENOENT:
            write(0,"No such file or directory.\n",27);
            break; 
        case EACCES:
            write(0,"Access denied.\n",15);
            break;
        default:
            write(0,"Unknown error\n",14);
            break;
    }
    _exit(1);
}
void dchk(int f){
    struct stat fs;
    fstat(f,&fs);
    if(S_ISDIR(fs.st_mode)){
        write(0,"It's a directory.\n",18);
        close(f);
        _exit(1);
        }
}