bash - [ : ==: unary operator expected-bash

Question

我正在尝试读取包含以下内容的文本文件 sport.txt，并尝试将用户输入与文本文件中找到的运动名称相匹配。

如果找到它会打印“找到运动”，如果没有找到它会打印“找不到运动”。

显示的第一个示例看起来几乎完美，直到我尝试键入一个随机单词并显示错误:

[: ==: unary operator expected

我还尝试在显示的第二个示例中使用 "" 作为变量，但它只会打印“未找到运动”，即使我输入了与运动名称完全匹配的运动名称在文本文件中。

文件 sports.txt

cycling
swimming
batmintion

代码(例1)

#!/bin/bash
file="sports.txt"
read -p "Enter a sports name": sportsName
existingSports=$(grep $sportsName $file);
if [ $existingSports == $sportsName ]; then
     echo "Sports Found"
else
     echo "No Sports Found"
fi

如果我根据上面的代码输入'swimming'，输出是:

Sports Found

现在如果我输入“swim”，输出是:

No Sports Found

如果我输入一个随机词“asd”，输出是:

[: ==: unary operator expected
No Sports Found

代码(例2)

#!/bin/bash
file="sports.txt"
read -p "Enter a sports name": sportsName
existingSports=$(grep $sportsName $file);
if [ "$existingSports" == "$sportsName" ]; then
     echo "Sports Found"
else
     echo "No Sports Found"
fi

如果我根据上面的代码输入'swimming'，输出是:

No Sports Found

现在如果我输入“swim”，输出是:

No Sports Found

代码(例3)

#!/bin/bash
file="sports.txt"
read -p "Enter a sports name": sportsName
existingSports=$(grep $sportsName $file);
if [[ "$existingSports" == "$sportsName" ]]; then
     echo "Sports Found"
else
     echo "No Sports Found"
fi

如果我根据上面的代码输入'swimming'，输出是:

No Sports Found

现在如果我输入“swim”，输出是:

No Sports Found

如前所述，第一个示例几乎接近预期。我应该怎么做才能摆脱错误消息？

Answer 1

代替这个 block :

existingSports=$(grep $sportsName $file);
if [ $existingSports == $sportsName ]; then
     echo "Sports Found"
else 
     echo "No Sports Found"
fi

您可以使用 grep -q 和 word boundaries 并将您的代码减少到单行:

grep -q "\<$sportsName\>" "$file" && echo "Sports Found" || echo "No Sports Found"

根据man grep:

-q, --quiet, --silent

Quiet; do not write anything to standard output. Exit immediately
with zero status if any match is found, even if an error was detected.