Linux Shell 脚本:if/else 适用于 bash，但不适用于 zsh 或 sh

Question

这是我正在编写的安装程序，删除了所有不相关的位：

#!/bin/bash
echo "In the prompt below, type 'install' or 'remove' (without the quotes)"
echo "If you type neither, this script will terminate."
read -p "Action to perform: " OPERATION
if [ "$OPERATION" == "install" ]
then
echo "Installing..."
echo "Install successful!"
elif [ "$OPERATION" == "remove" ]
then
echo "Removing..."
echo "Remove successful!"
else
echo "Aborting with no actions"
fi

此脚本完全按照您的预期工作。当我键入install时，安装部分执行，当我键入remove删除部分执行，最后当我键入随机字符时，它会中止。

但是相同的脚本将#!/bin/bash替换为#!/bin/sh或留空(我的常规shell是ZSH)，它出错了：

In the prompt below, type 'install' or 'remove' (without the quotes)
If you type neither, this script will terminate.
Action to perform: sdfsdfdsf
./test.sh: 7: [: sdfsdfdsf: unexpected operator
./test.sh: 11: [: sdfsdfdsf: unexpected operator
Aborting with no actions

对于某些上下文，我在Ubuntu Studio 18.04上，zsh --version打印zsh 5.4.2 (x86_64-ubuntu-linux-gnu)。

有人可以帮助我理解为什么会发生这种情况吗？

Answer 1

在 ubuntu 18.04 上，/bin/sh是指向[ ... ]不支持==/bin/dash的符号链接。您可以使用也适用于 zsh 的[ = ]。

[STEP 101] # grep 18.04 /etc/os-release
VERSION="18.04.2 LTS (Bionic Beaver)"
PRETTY_NAME="Ubuntu 18.04.2 LTS"
VERSION_ID="18.04"
[STEP 102] # ls -l /bin/sh
lrwxrwxrwx 1 root root 4 2019-02-14 09:49 /bin/sh -> dash
[STEP 103] # /bin/sh
# [ a == b ]
/bin/sh: 1: [: a: unexpected operator
# test a == b
/bin/sh: 2: test: a: unexpected operator
# [ a = b ]
# test a = b
# exit
[STEP 104] #

请注意，POSIX只提到了"="，并且根据dash手册，">只有POSIX指定的功能，加上一些Berkeley扩展，才被合并到这个shell中。

Answer 2

拳头您应该更新您的 shebang 以使用sh而不是bash然后您将不得不使用稍微不同的语法。您可以使用 shellcheck 来查看详细错误。

文章的语气描述了这种差异，例如： https://stackoverflow.com/a/5725402/3872881

#!/bin/sh
echo "In the prompt below, type 'install' or 'remove' (without the quotes)"
echo "If you type neither, this script will terminate."
echo -n "Action to perform: "
read -r OPERATION
if [ "$OPERATION" = "install" ]
then
echo "Installing..."
echo "Install successful!"
elif [ "$OPERATION" = "remove" ]
then
echo "Removing..."
echo "Remove successful!"
else
echo "Aborting with no actions"
fi