是否有一种简单的方法来为一个glob设置nullglob [英] Is there an easy way to set nullglob for one glob

问题描述

在bash中，如果您这样做:

In bash, if you do this:

mkdir /tmp/empty
array=(/tmp/empty/*)

您发现array现在有一个元素"/tmp/empty/*"，而不是您想要的零.幸运的是，可以通过使用shopt -s nullglob

you find that array now has one element, "/tmp/empty/*", not zero as you'd like. Thankfully, this can be avoided by turning on the nullglob shell option using shopt -s nullglob

但是nullglob是全局的，并且在编辑现有的shell脚本时可能会破坏某些内容(例如，是否有人检查了ls foo*的退出代码以检查是否存在以"foo"开头的文件?).因此，理想情况下，我只想在很小的范围内打开它-理想情况下是一个文件名扩展.您可以使用shopt -u nullglob再次将其关闭，但是当然只有在之前将其禁用时:

But nullglob is global, and when editing an existing shell script, may break things (e.g., did someone check the exit code of ls foo* to check if there are files named starting with "foo"?). So, ideally, I'd like to turn it on only for a small scope—ideally, one filename expansion. You can turn it off again using shopt -u nullglob But of course only if it was disabled before:

old_nullglob=$(shopt -p | grep 'nullglob$')
shopt -s nullglob
array=(/tmp/empty/*)
eval "$old_nullglob"
unset -v old_nullglob

使我认为必须有更好的方法.显然，将其放入子外壳"是行不通的，因为变量赋值当然会随子外壳一起消失.除了正在等待Austin组导入ksh93语法之外，还有吗?

makes me think there must be a better way. The obvious "put it in a subshell" doesn't work as of course the variable assignment dies with the subshell. Other than waiting for the Austin group to import ksh93 syntax, is there?

推荐答案

使用Bash 4中的mapfile，您可以从子外壳中加载数组，例如:mapfile array < <(shopt -s nullglob; for f in ./*; do echo "$f"; done).完整示例:

With mapfile in Bash 4, you can load an array from a subshell with something like: mapfile array < <(shopt -s nullglob; for f in ./*; do echo "$f"; done). Full example:

$ shopt nullglob
nullglob        off
$ find
.
./bar baz
./qux quux
$ mapfile array < <(shopt -s nullglob; for f in ./*; do echo "$f"; done)
$ shopt nullglob
nullglob        off
$ echo ${#array[@]}
2
$ echo ${array[0]}
bar baz
$ echo ${array[1]}
qux quux
$ rm *
$ mapfile array < <(shopt -s nullglob; for f in ./*; do echo "$f"; done)
$ echo ${#array[@]}
0

• 在使用echo打印文件名时，请确保使用./*而不是裸露的*进行滚动显示
• 不适用于文件名:( derobert
中指出的换行符
• Be sure to glob with ./* instead of a bare * when using echo to print the file name
• Doesn't work with newline characters in the filename :( as pointed out by derobert

如果您需要处理文件名中的换行符，则必须做得更加冗长:

If you need to handle newlines in the filename, you will have to do the much more verbose:

array=()
while read -r -d $'\0'; do
    array+=("$REPLY")
done < <(shopt -s nullglob; for f in ./*; do printf "$f\0"; done)

但是到这一点，遵循其他答案之一的建议可能会更简单.

But by this point, it may be simpler to follow the advice of one of the other answers.

这篇关于是否有一种简单的方法来为一个glob设置nullglob的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！