Bash：变量未在 if 中设置

问：

第一次尝试 Linux，学习 Bash 只是为了好玩。尝试编写脚本。

这是我的一段代码（bash）：

sudo pacman -Suy | if grep --color=always -e "^" -e "there is nothing to do"; then pup=0; else pup=1; fi; 

当我尝试回显变量时，没有任何返回。我已经通过多种方式确认根本没有设置变量。当我尝试将其从 if 语句中设置出来时，echo $var 工作得很好。

这是我的上下文代码的很大一部分：

case $yn in
        [yY] ) echo running only yay -Suy;
           echo running...;
           yay -Suy | if grep --color=always -e "^" -e "there is nothing to do"; then yup=0; else yup=1; fi; 
           break;;
        [nN] ) echo not updating;
           echo exiting...;
           exit;;
        [pP] ) running only pacman -Suy;
           echo running...;
           sudo pacman -Suy | if grep --color=always -e "^" -e "there is nothing to do"; then pup=0; else pup=1; fi;
           break;;
        [bB] ) echo running full sys update;
           echo running...;
           sudo pacman -Suy | if grep --color=always -e "^" -e "there is nothing to do"; then pup=0; else pup=1; fi; 
           yay -Suy | if grep --color=always -e "^" -e "there is nothing to do"; then yup=0; else yup=1; fi;
           break;;
        * ) echo invalid response;;
esac

done

if [ "$pup" -eq 1 ]; then
   echo "Pacman has updated something."
elif [ "$pup" -eq 0 ]; then
   echo "Pacman has not updated anything."
else
   :
fi
if [ "$yup" -eq 1 ]; then
   echo "Yay has updated something."
elif [ "$yup" -eq 0 ]; then
   echo "Yay has not updated anything."
else
   :
fi

成为单行本不是问题。当我用“echo '0'”替换 pup=0 时，它返回 0 没问题。我试着摆弄最后一个if语句，但没有变化。