当给定一个不带glob字符的字符串时,为什么Perl的glob()函数总是返回文件名? [英] Why does Perl's glob() function always return a file name when given a string with no globbing characters?
问题描述
我给Perl的glob
函数提供了一个清单列表和一个字符串.全局问题已按预期方式处理,但始终可以找到字符串.例如:
I gave a list of globs and one string to Perl's glob
function. The globs were treated as expected but the string is always found. For example:
$ ls
foo
$ perl -le '@files=glob("*bar"); print @files' ## prints nothing, as expected
$ perl -le '@files=glob("bar"); print @files'
bar
如上所示,即使没有这样的文件,第二个示例也会打印bar
.
As you can see above, the second example prints bar
even though no such file exists.
我的第一个想法是,它的行为类似于shell,因为当没有扩展可用时,一个glob(或被视为glob的东西)会自行扩展.例如,在csh
中(很糟糕,这就是Perl的glob()
函数所遵循的,请参见下面的引号):
My first thought is that it behaves like the shell in that when no expansion is available, a glob (or something being treated as a glob) expands to itself. For example, in csh
(awful as it is, this is what Perl's glob()
function seems to be following, see the quote below):
% foreach n (*bar*)
foreach: No match.
% foreach n (bar)
foreach? echo $n
foreach? end
bar ## prints the string
但是,根据文档,glob
应该返回文件名扩展名(强调我的意思):>
However, according to the docs, glob
should return filename expansions (emphasis mine):
在列表上下文中,返回EXPR值的文件名扩展列表(可能为空),例如标准Unix shell/bin/csh会执行的操作.
In list context, returns a (possibly empty) list of filename expansions on the value of EXPR such as the standard Unix shell /bin/csh would do.
那么当传递给glob
的参数中没有浮点字符时,为什么会返回自身?这是错误还是我做错了什么?
So why is it returning itself when there are no globbing characters in the argument passed to glob
? Is this a bug or am I doing something wrong?
推荐答案
我想我希望Perl在后台检查文件是否存在.
I guess I expected Perl to be checking for file existence in the background.
Perl 正在检查文件是否存在:
Perl is checking for file existence:
$ strace perl -e'glob "foo"' 2>&1 | grep foo
execve("/home/mcarey/perl5/perlbrew/perls/5.24.0-debug/bin/perl", ["perl", "-eglob \"foo\""], [/* 39 vars */]) = 0
lstat("foo", {st_mode=S_IFREG|0664, st_size=0, ...}) = 0
那么当传递给glob的参数中没有glob字符时为什么会返回自身?
So why is it returning itself when there are no globbing characters in the argument passed to glob?
因为那是csh所做的. Perl的glob
实现基于 glob(3)启用了GLOB_NOMAGIC
标志:
Because that's what csh does. Perl's implementation of glob
is based on glob(3) with the GLOB_NOMAGIC
flag enabled:
GLOB_NOMAGIC
与GLOB_NOCHECK相同,但仅在不包含任何特殊字符*
,?
或[
的情况下才追加模式.提供GLOB_NOMAGIC是为了简化实现历史性的csh(1)全局行为,并且可能不应该在其他任何地方使用.
Is the same as GLOB_NOCHECK but it only appends the pattern if it does not contain any of the special characters *
, ?
or [
. GLOB_NOMAGIC is provided to simplify implementing the historic csh(1) globbing behavior and should probably not be used anywhere else.
GLOB_NOCHECK
如果pattern与任何路径名都不匹配,则glob()返回仅包含pattern的列表...
If pattern does not match any pathname, then glob() returns a list consisting of only pattern...
因此,对于像foo
这样的没有通配符的模式:
So, for a pattern like foo
with no wildcards:
- 如果存在匹配的文件,则返回文件名扩展名(
foo
) - 如果不存在匹配文件,则返回模式(
foo
)
- if a matching file exists, the filename expansion (
foo
) is returned - if no matching file exists, the pattern (
foo
) is returned
由于文件名扩展名与模式相同,
Since the filename expansion is the same as the pattern,
glob 'foo'
不论文件foo
是否存在,列表上下文中的
总是返回带有单个元素foo
的列表.
in list context will always return a list with the single element foo
, whether the file foo
exists or not.
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