如何从bash脚本中的Docker容器中运行的脚本获取USB设备信息？

Question

我制作了一个受巴莱纳-储存启发的巴莱纳-储存文件。当我通过我正在部署的balena.io仪表板登录到容器(可能在其他地方相同)并手动运行脚本时，它就可以工作了。当容器在启动时运行脚本(运行脚本的脚本)时，它会挂起未填充的变量。我认为这是一个权限问题或脚本运行脚本的事情。我不知道如何继续读取USB设备变量。

mount.sh：

# Automatically mount a USB drive by specified volume name.
# Note: make sure to have USB_VOLUME_NAME set in env vars.
# Thanks: https://github.com/balena-io-playground/balena-storage

echo "Checking for USB_VOLUME_NAME..."

echo "A"

if [[ -z $USB_VOLUME_NAME ]]; then
  echo "Make sure to set environment variable USB_VOLUME_NAME in order to find a connected USB drive by that label and connect to it. Exiting..." >> /usr/src/app/mount.log
  exit 1
fi

echo "B"

# Get device by label env var set in balena.io dashboard device env vars
USB_DEVICE=$(blkid -L $USB_VOLUME_NAME)
if [[ -z $USB_DEVICE ]]; then
  echo "Invalid USB_DEVICE name: $USB_DEVICE" >> /usr/src/app/mount.log
  exit 1
fi

echo $USB_DEVICE

echo "C"

# Get extra device info
ID_FS_TYPE=${ID_FS_TYPE:=$(/bin/udevadm info -n $USB_DEVICE | /usr/bin/awk -F "=" '/ID_FS_TYPE/{ print $2 }')}
ID_FS_UUID_ENC=${ID_FS_UUID_ENC:=$(/bin/udevadm info -n $USB_DEVICE | /usr/bin/awk -F "=" '/ID_FS_UUID_ENC/{ print $2 }')}
ID_FS_LABEL_ENC=${ID_FS_LABEL_ENC:=$(/bin/udevadm info -n $USB_DEVICE | /usr/bin/awk -F "=" '/ID_FS_LABEL_ENC/{ print $2 }')}

MOUNT_POINT=/mnt/$USB_VOLUME_NAME

echo $ID_FS_TYPE
echo $ID_FS_UUID_ENC
echo $ID_FS_LABEL_ENC
echo $MOUNT_POINT

echo "D"

# Bail if file system is not supported by the kernel
if ! /bin/grep -qw $ID_FS_TYPE /proc/filesystems; then
  echo "File system not supported: $ID_FS_TYPE" >> /usr/src/app/mount.log
  exit 1
fi

echo "E"

# Mount device
if /bin/findmnt -rno SOURCE,TARGET $USB_DEVICE >/dev/null; then
    echo "Device $USB_DEVICE is already mounted!" >> /usr/src/mount.log
else
    echo "Mounting - Source: $USB_DEVICE - Destination: $MOUNT_POINT" >> /usr/src/app/mount.log
    /bin/mkdir -p $MOUNT_POINT
    /bin/mount -t $ID_FS_TYPE -o rw $USB_DEVICE $MOUNT_POINT
fi

echo "F"

当容器运行脚本时，它会停留在"D“之后，ID_FS_TYPE、ID_FS_UUID_ENC和ID_FS_LABEL_ENC都是空的(这是挂起的一个很好的理由)。

产出：

Checking for USB_VOLUME_NAME...
A
B
/dev/sda1
C



/mnt/MYDRIVE
D

我的dockerfile.template：

FROM balenalib/%%BALENA_MACHINE_NAME%%-node

# Enable udev for detection of dynamically plugged devices
ENV UDEV=on
COPY udev/usb.rules /etc/udev/rules.d/usb.rules

# Install dependencies
RUN install_packages util-linux

WORKDIR /usr/src/app

# Move scripts used for mounting USB
COPY scripts scripts
RUN chmod +x scripts/*

# server.js will run when container starts up on the device
CMD ["/bin/bash", "/usr/src/app/scripts/start.sh"]

start.sh：

echo "Mounting USB drive..."
cd /usr/src/app/scripts
/bin/bash mount.sh

# It won't get this far while the script above hangs.
echo "Starting server..."
cd /usr/src/app
/usr/local/bin/yarn run serve

我可以确认，在从容器中手动运行时，所有操作都正常：

cd /usr/src/app/scripts
/bin/bash mount.sh

输出：

Checking for USB_VOLUME_NAME...
A
B
/dev/sda1
C
vfat
BE23-31BA
MYDRIVE
/mnt/MYDRIVE
D
E
F
(and the drive mounted)

如何解析空变量？

Answer 1

始终引用您使用的每个shell变量。(除非您完全确定您在做什么，以及如果变量值为空或包含空格，则会发生什么。)

没有引用，当你

/bin/grep -qw $ID_FS_TYPE /proc/filesystems

而$ID_FS_TYPE是空的，这个单词在命令行中被省略了，所以

/bin/grep -qw /proc/filesystems

它使用/proc/filesystems作为regexp，并尝试通过stdin实现grep；这将导致明显的挂起。

如果你引用它：

/bin/grep -qw "$ID_FS_TYPE" /proc/filesystems

它将获得一个空字符串作为regexp参数，一个文件名作为输入参数，这将很小地成功(但不会挂起)。

出于类似的原因，如果$USB_VOLUME_NAME未设置，我希望您会得到一个shell语法错误，如果变量名中有一个空格，整个脚本就会很奇怪。