回声在 if 中工作吗？

Question

考虑以下函数：

function testForBinary {
    someBin=$(command -v binary)
        # Test if binary is installed
        if [[ -n $someBin ]]; then
            installSuccess="Success"
            echo ${installSuccess}
            return
        else
            # This should never be reached
            return 1
        fi
}

取自（上下文）：

function installAndTestForDialog() {
# dialog allows me to create a pretty installer
# It is a required dependency since XXXXX
# Name Removed as I'm attempting modularization
# of a script from Github that's one huge Script

# See https://unix.stackexchange.com/questions/85249/why-not-use-which-what-to-use-then
    local dialogBin
    local updated=false
    local dialogInstallSuccess

    dialogBin=$(command -v dialog)
    if [[ -z $dialogBin ]]; then
        printf "Installing dialog... "
        if [[ $updated -eq 0 ]]; then
            apt-get update > /dev/null 2>&1
            updated=true
        fi
        # Debian Based OS
        apt-get -y install dialog > /dev/null 2>&1

        # Test if dialog is installed to verify installation
        # above was successful.
        dialogBin=$(command -v dialog)
        if [[ -n $dialogBin ]]; then
            # I cannot get this to echo success
            # if I echo from here
            dialogInstallSuccess="Success"
            # Moving it here doesn't help either  Why??
            echo ${dialogInstallSuccess}
            return
        else
            # This should never be reached
            return 1
        fi
    fi    
}    

我试图将其installSuccess视为布尔值，但我做错了什么。如果我像上面那样写函数，然后添加：

isInstalled=$(testForBinary)
echo "$isInstalled"

isInstalled返回一个空行。我知道这不是真的，因为当我command -v binary在函数之外运行时，binary结果的路径。

输出（上下文）：

Function and Variable Output Test
=====================
# These are other tests
# I'm performing, but note
# the blank line, which should
# print Success 
2.9-MODULAR
192.168.1.227
false
false
(blank line)

Answer 1

这不需要像您制作的那样复杂和脆弱。

installAndTestForDialog() {
  if command -v dialog &> /dev/null; then
    return 0
  else
    apt-get update &> /dev/null
    apt-get -y install dialog &> /dev/null
  fi
}

如果对话框已安装，该函数将返回 0。否则，它将尝试安装它并返回apt-get install命令的退出代码。

正如@muru 在评论中指出的那样，这可以浓缩为：

if ! command -v dialog; then
    apt-get update
    apt-get install -y dialog
fi > /dev/null 2>&1

或者只是尝试安装它而不必检查它是否已经安装：

{ apt-get update && apt-get -y --no-upgrade install dialog ;} >/dev/null 2>&1

如果已安装，该--no-upgrade选项将阻止dialog升级。