Resolve length limit with xb command in gdb - gdb

Question

I need to copy the hex bytes in xb command, but gdb print them in multiple lines, and I had to remove the memory address from the output
(gdb) x/20xb 0x00007ffff7e84000
0x7ffff7e84000 <opendir>: 0xf3 0x0f 0x1e 0xfa 0x41 0x55 0x41 0x54
0x7ffff7e84008 <opendir+8>: 0x55 0x53 0x48 0x81 0xec 0xa8 0x00 0x00
0x7ffff7e84010 <opendir+16>: 0x00 0x64 0x48 0x8b
Tried set width unlimited but it didn't work.
What should I do?
EDIT
Full session while testing Employed Russian's solution:
# gdb /bin/ls
Reading symbols from /bin/ls...
(No debugging symbols found in /bin/ls)
(gdb) b opendir
Breakpoint 1 at 0x4870
(gdb) r
Starting program: /usr/bin/ls
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Breakpoint 1, 0x00007ffff7e84000 in opendir () from /lib/x86_64-linux-gnu/libc.so.6
(gdb) define xb
Type commands for definition of "xb".
End with a line saying just "end".
> set var $j = 0
> while $j < $arg1
> printf "0x%02x ", (char *) $arg0[$j++]
> end
> printf "\n"
>end
(gdb) xb 0x00007ffff7e84000 20
cannot subscript something of type `long'
(gdb)

Answer 1

Test program:
int main()
{
char buf[] = "abcdefghijklmopqrstuvwxyz";
return 0;
}
gcc -g t.c
cat > xb.txt <<'EOF'
define xb
set var $j = 0
while $j < $arg1
printf "0x%02x ", ((char *) $arg0)[$j++] & 0xFF
end
printf "\n"
end
EOF
gdb -q -x xb.txt ./a.out
Reading symbols from ./a.out...
(gdb) start
Temporary breakpoint 1 at 0x1129: file t.c, line 3.
Starting program: /tmp/a.out
Temporary breakpoint 1, main () at t.c:3
3 char buf[] = "abcdefghijklmnopqrstuvwxyz";
(gdb) n
4 return 0;
(gdb) x/16bx buf
0x7fffffffdad0: 0x61 0x62 0x63 0x64 0x65 0x66 0x67 0x68
0x7fffffffdad8: 0x69 0x6a 0x6b 0x6c 0x6d 0x6e 0x6f 0x70
(gdb) xb buf 16
0x61 0x62 0x63 0x64 0x65 0x66 0x67 0x68 0x69 0x6a 0x6b 0x6c 0x6d 0x6e 0x6f 0x70
(gdb) xb buf 27
0x61 0x62 0x63 0x64 0x65 0x66 0x67 0x68 0x69 0x6a 0x6b 0x6c 0x6d 0x6e 0x6f 0x70 0x71 0x72 0x73 0x74 0x75 0x76 0x77 0x78 0x79 0x7a 0x00