如果文件名glob不匹配,如何不匹配 [英] How to match nothing if a file name glob has no matches
问题描述
我想遍历所有与扩展名jpg
或txt
匹配的文件.我使用:
I want to loop over all files matching extension jpg
or txt
. I use:
for file in myDir/*.{jpg,txt}
do
echo "$file"
done
问题::如果目录中根本不包含jpg文件,则循环将进行一次迭代,输出为myDir/*.jpg
.我认为*
将被任意文件替换(如果不存在文件,则无法扩展).如何避免不必要的迭代?
Problem: If the directory contains no jpg file at all, the loop will have one iteration with output myDir/*.jpg
. I thought *
will be replaced by an arbitrary file (and if no file exists it cannot be expanded). How can I avoid the unwanted iteration?
推荐答案
使用它来避免不必要的迭代:
Use this to avoid the unwanted iteration:
shopt -s nullglob
来自man bash
:
nullglob
:如果设置了bash,则bash允许不匹配任何文件的模式(请参见上面的路径名扩展)扩展为空字符串,而不是扩展为它们自己.
nullglob
: If set, bash allows patterns which match no files (see Pathname Expansion above) to expand to a null string, rather than themselves.
请参阅:help shopt
和shopt
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