[uEnv.txt]在uEnv.txt文件中使用if语句实现Image/dtb文件切换

bootdir=
bootfile=zImage
fdtfile=embest-SBCC_PH8800_WLQ.dtb
loadaddr=0x82000000
fdtaddr=0x88000000

finduuid=part uuid mmc ${mmcdev}:2 uuid
loadfdt=fatload mmc ${mmcdev}:1 ${fdtaddr} ${fdtfile}
loaduimage=fatload mmc ${mmcdev}:1 ${loadaddr} ${bootfile}

uenvcmd=mdio write 7 0 0x800; mmc rescan; run loaduimage; run loadfdt; run fdtboot
fdtboot=run mmc_args; bootz ${loadaddr} - ${fdtaddr}
mmc_args=run finduuid; setenv bootargs console=ttyS0,115200n8 loglevel=0 systemd.log_target=null systemd.journald.forward_to_console=0 ${optargs} root=PARTUUID=${uuid} rw rootfstype=${mmcrootfstype}

bootdir=
bootfile=zImage
fdtfile=embest-SBCC_PH8800_WLQ.dtb
loadaddr=0x82000000
fdtaddr=0x88000000

finduuid=part uuid mmc ${mmcdev}:2 uuid

recoveryflag=false

uenvcmd=if test ${recoveryflag} = "true"; then setenv bootfile zImage_bak; setenv fdtfile embest-SBCC_PH8800_WLQ_bak.dtb; echo bootfile=${bootfile} fdtfile=${fdtfile}; fi; setenv loadfdt fatload mmc ${mmcdev}:1 ${fdtaddr} ${fdtfile}; setenv loaduimage fatload mmc ${mmcdev}:1 ${loadaddr} ${bootfile}; mdio write 7 0 0x800; mmc rescan; run loaduimage; run loadfdt; run fdtboot

fdtboot=run mmc_args; bootz ${loadaddr} - ${fdtaddr}
mmc_args=run finduuid; setenv bootargs console=ttyS0,115200n8 loglevel=0 systemd.log_target=null systemd.journald.forward_to_console=0 ${optargs} root=PARTUUID=${uuid} rw rootfstype=${mmcrootfstype} 

mount -o remount,rw /boot/firmware

固件更新成功：(注意-i和语句中的三个斜杠)
sed -i ‘s/recoveryflag=true/recoveryflag=false/‘ /boot/firmware/uEnv.txt

固件更新失败：
sed -i ‘s/recoveryflag=false/recoveryflag=true/‘ /boot/firmware/uEnv.txt
sync

mount -o remount,ro /boot/firmware