结合两个 Bash while 循环语句

Question

我试图在一个 while 循环中组合 2 个不同的逻辑语句，但是无法正确地获取逻辑，以便可以在 same 循环中评估 2 个不同的检查。例如，我有以下 2 条逻辑语句。

逻辑 1

判断输入的用户名是否为空，是否要求用户重新输入不同的用户名。

echo -ne "User Name [uid]$blue:$reset "
read USERNAME
USERNAME=$(echo "$USERNAME" | tr "[:upper:]" "[:lower:]")
while [[ -z "$USERNAME" ]]; do
        echo ""
        printf "%s\n" "The User Name CAN NOT be blank"
        echo ""
        echo -ne "User Name [uid]$blue:$reset "
        read USERNAME;
        USERNAME=$(echo "$USERNAME" | tr "[:upper:]" "[:lower:]")
done

逻辑 2

确定读取的用户名是否已经存在以及是否要求用户重新输入用户名。

echo -ne "User Name [uid]$blue:$reset "
read USERNAME
USERNAME=$(echo "$USERNAME" | tr "[:upper:]" "[:lower:]")
$(command -v getent) passwd "$USERNAME" &>/dev/null
while [[ $? -eq 0 ]]; do
        echo ""
        printf "%s\n" "$USERNAME exists in LDAP"
        echo ""
        echo -ne "User Name [uid]$blue:$reset "
        read USERNAME;
        USERNAME=$(echo "$USERNAME" | tr "[:upper:]" "[:lower:]")
        $(command -v getent) passwd "$USERNAME" &>/dev/null
done

为了实现所描述的目标，我尝试了while 循环和嵌套if 语句，但此时我很困惑。基本上作为脚本的一部分，当要求用户输入用户名而不退出脚本直到输入有效值时，我希望将这两个逻辑语句组合起来。

Answer 1

不要使用大写的变量名！

#!/bin/bash
while true; do
    echo -ne "User Name [uid]$blue:$reset "
    read username
    [ -z "$username" ] && echo -e "\nThe User Name CAN NOT be blank\n" && continue
    username=$(tr [:upper:] [:lower:] <<< $username)
    [ -z $(getent passwd "$username") ] && break || echo -e "\n$username exists in LDAP\n"
done

Answer 2

您可以将条件检查从 while 语句移到一对 if 语句中。在这种情况下，我还将读取和相关命令移至循环顶部。这意味着您在循环之前不需要额外的读取命令。

#!/bin/bash
while true; do
    echo -ne "User Name [uid]$blue:$reset "
    read username;
    username=$(echo "$username" | tr "[:upper:]" "[:lower:]")
    $(command -v getent) passwd "$username" &>/dev/null

    if [[ -z "$username" ]]; then
        echo ""
        printf "%s\n" "The User Name CAN NOT be blank"
        echo ""
        continue #Skips the rest of the loop and starts again from the top.
    fi

    if [[ $? -eq 0 ]]; then
        echo ""
        printf "%s\n" "$username exists in LDAP"
        echo ""
        continue #Skips the rest of the loop and starts again from the top.
    fi

    #If execution reaches this point, both above checks have been passed
    break #exit while loop, since we've got a valid username
done

顺便说一句，通常建议避免使用大写的变量名，以避免与系统环境变量发生冲突。