没有匹配文件时如何跳过for循环? [英] How to skip the for loop when there are no matching files?

问题描述

当我遍历所有以 foo 开头的文件时，我会

When I loop through all the files starting by foo I do

for f in foo* ; do echo "result = $f" ; done

问题是当 no file 以 foo 开头时，我得到:

The problem is when no file start by foo I get:

result = foo*

表示循环执行一次，即使没有文件以foo开头.

Meaning that the loop is executed once, even if no file start by foo.

这怎么可能?如何遍历所有文件(如果没有文件则根本不循环)?

How is this possible? How can I loop through all files (and not loop at all if there is no file)?

推荐答案

您可以通过设置 nullglob:

shopt -s nullglob

来自链接页面:

nullglob 是一个修改 [[glob]] 扩展的 Bash shell 选项这样不匹配任何文件的模式扩展到零参数，而不是对他们自己.

nullglob is a Bash shell option which modifies [[glob]] expansion such that patterns that match no files expand to zero arguments, rather than to themselves.

您可以使用 -u 删除此设置(未设置，而 s 用于设置):

You can remove this setting with -u (unset, whereas s is for set):

shopt -u nullglob

测试

$ touch foo1 foo2 foo3
$ for file in foo*; do echo "$file"; done
foo1
foo2
foo3
$ rm foo*

让我们看看:

$ for file in foo*; do echo "$file"; done
foo*

设置nullglob:

$ shopt -s nullglob
$ for file in foo*; do echo "$file"; done
$

然后我们禁用该行为:

$ shopt -u nullglob
$ for file in foo*; do echo "$file"; done
foo*

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