如何在此脚本中打破无限循环

Question

我正在用 bash 做一些有趣的事情

我在下面写了脚本：

#!/bin/bash
while :
do
    if [ -s /tmp/file.txt ]; then
        for line in $(cat /tmp/file.txt)
        do
            echo $line
            #May be some commands here
        done
    fi
done

我的file.txt的内容是：

1 True
2 Flase

如果命令cat /tmp/file.txt 已完成（我的意思是所有行都已读取）并且echo $line 和其他命令已完成然后break 不定式while : 循环，我该如何说脚本？

谢谢

Answer 1

使用break。

#!/bin/bash
while :
do
    if [ -s /tmp/file.txt ]; then
        for line in $(cat /tmp/file.txt)
        do
            echo $line
            #May be some commands here
        done
        break
    fi
done

虽然这样会更简单，更合适：

#!/bin/bash
for (( ;; )); do
    if [[ -s /tmp/file.txt ]]; then
        # Never use `for X in $()` when reading output/input. Using word splitting
        # method for it could be a bad idea in many ways. One is it's dependent with
        # IFS. Second is that glob patterns like '*' could be expanded and you'd
        # produce filenames instead.
        while read line; do
            # Place variables between quotes or else it would be subject to Word
            # Splitting and unexpected output format could be made.
            echo "$line"
        done < /tmp/file.txt
        break
    fi
done

另一方面，你真的需要外循环吗？这次不用break了。

#!/bin/bash
if [[ -s /tmp/file.txt ]]; then
    while read line; do
        echo "$line"
    done < /tmp/file.txt
fi