A bug when using bash shell variable

[ju nan]

I hava run into some troubles when I use bash shell to execute qemu, here is 
the log.



  1.  Run qemu with arguments directly in bash shell, I use strace to track 
execve syscall, everything goes well

junan@u0:~/Documents/coding/run-riscv-qemu-linux$ strace qemu-system-riscv64 
-nographic -machine virt -kernel ../linux-5.11/arch/riscv/boot/Image -append 
"root=/dev/vda ro console=ttyS0" -drive file=root.ext4,format=raw,id=hd0 
-device virtio-blk-device,drive=hd0
execve("/usr/bin/qemu-system-riscv64", ["qemu-system-riscv64", "-nographic", 
"-machine", "virt", "-kernel", "../linux-5.11/arch/riscv/boot/Im"..., 
"-append", "root=/dev/vda ro console=ttyS0", "-drive", 
"file=root.ext4,format=raw,id=hd0", "-device", "virtio-blk-device,drive=hd0"], 
0x7ffc39cda858 /* 58 vars */) = 0
brk(NULL)                               = 0x55bb77e20000
arch_prctl(0x3001 /* ARCH_??? */, 0x7ffd61474450) = -1 EINVAL (Invalid argument)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3


  1.  But when I use bash variables to do it again, something wired happend, as 
you can see, the argument "root=/dev/vda ro console=ttyS0" is splited into 
different parts, so qemu did not start successfully 😋


junan@u0:~/Documents/coding/run-riscv-qemu-linux$ echo $QEMU
qemu-system-riscv64
junan@u0:~/Documents/coding/run-riscv-qemu-linux$ echo $QOPTIONS
-nographic -machine virt -kernel ../linux-5.11/arch/riscv/boot/Image -append 
"root=/dev/vda ro console=ttyS0" -drive file=root.ext4,format=raw,id=hd0 
-device virtio-blk-device,drive=hd0

junan@u0:~/Documents/coding/run-riscv-qemu-linux$ strace $QEMU $QOPTIONS
execve("/usr/bin/qemu-system-riscv64", ["qemu-system-riscv64", "-nographic", 
"-machine", "virt", "-kernel", "../linux-5.11/arch/riscv/boot/Im"..., 
"-append", "\"root=/dev/vda", "ro", "console=ttyS0\"", "-drive", 
"file=root.ext4,format=raw,id=hd0", "-device", "virtio-blk-device,drive=hd0"], 
0x7ffe1e71a928 /* 58 vars */) = 0
brk(NULL)                               = 0x5613dfdc4000


Thank you all for making so many excellent softwares, and I wish this will help 
to improve the bash shell 😊.