为什么glob lstat匹配条目？

Looking into behavior in this question, I was surprised to see that perl lstat()s every path matching a glob pattern:

在这个问题中查看行为,我很惊讶地看到perl lstat()的每个路径都与glob模式匹配:

$ mkdir dir
$ touch dir/{foo,bar,baz}.txt  
$ strace -e trace=lstat perl -E 'say $^V; <dir/b*>' 
v5.10.1
lstat("dir/baz.txt", {st_mode=S_IFREG|0664, st_size=0, ...}) = 0
lstat("dir/bar.txt", {st_mode=S_IFREG|0664, st_size=0, ...}) = 0

I see the same behavior on my Linux system with glob(pattern) and <pattern>, and with later versions of perl.

我在我的Linux系统上看到了与glob(模式)和以及更高版本的perl相同的行为。

My expectation was that the globbing would simply opendir/readdir under the hood, and that it would not need to inspect the actual pathnames it was searching.

我的期望是,globbing只是opendir / readdir,并且它不需要检查它正在搜索的实际路径名。

What is the purpose of this lstat? Does it affect the glob()s return?

这个lstat的目的是什么?它会影响glob()的返回吗?

2 个解决方案

#1

This strange behavior has been noticed before on PerlMonks. It turns out that glob calls lstat to support its GLOB_MARK flag, which has the effect that:

之前在PerlMonks上已经注意到这种奇怪的行为。事实证明,glob调用lstat来支持它的GLOB_MARK标志,其结果是:

Each pathname that is a directory that matches the pattern has a slash appended.

作为与模式匹配的目录的每个路径名都附加了一个斜杠。

To find out whether a directory entry refers to a subdir, you need to stat it. This is apparently done even when the flag is not given.

要确定目录条目是否引用了子目录,您需要对其进行统计。即使没有给出标志,这显然已经完成。

#2

I was wondering the same thing - "What is the purpose of this lstat? Does it affect the glob()s return?"

我想知道同样的事情 - “这个lstat的目的是什么?它会影响glob()的返回吗?”

Within bsd_glob.c glob2() I noticed a g_stat call within an if branch that required the GLOB_MARK flag to be set, I also noticed a call to g_lstat just before that was not guarded by a flag check. Both are within an if branch for when the end of pattern is reached. If I remove these 2 lines in the glob2 function in perl-5.12.4/ext/File-Glob/bsd_glob.c

在bsd_glob.c glob2()中,我注意到在if分支中需要设置GLOB_MARK标志的g_stat调用,我还注意到在没有被标志检查保护之前调用g_lstat。当达到模式结束时,两者都在if分支内。如果我在perl-5.12.4 / ext / File-Glob / bsd_glob.c中的glob2函数中删除这两行

- if (g_lstat(pathbuf, &sb, pglob))
-     return(0);

the only perl test (make test) that fails is test 5 in ext/File-Glob/t/basic.t with:

唯一失败的perl测试(make test)是ext / File-Glob / t / basic.t中的test 5:

not ok 5
#   Failed test at ../ext/File-Glob/t/basic.t line 92.
#     Structures begin differing at:
#          $got->[0] = 'asdfasdf'
#     $expected->[0] = Does not exist

Test 5 in t/basic.t is

t / basic.t中的测试5是

# check nonexistent checks
# should return an empty list
# XXX since errfunc is NULL on win32, this test is not valid there
@a = bsd_glob("asdfasdf", 0);
SKIP: {
    skip $^O, 1 if $^O eq 'MSWin32' || $^O eq 'NetWare';
    is_deeply(\@a, []);
}

If I replace the 2 lines removed with:

如果我用以下内容替换掉2行:

+   if (!((pglob->gl_flags & GLOB_NOCHECK) ||
+         ((pglob->gl_flags & GLOB_NOMAGIC) &&
+          !(pglob->gl_flags & GLOB_MAGCHAR)))){
+     if (g_lstat(pathbuf, &sb, pglob))
+       return(0);
+   }

I don't see any failures from "make test" for perl-5.12.4 on linux x86_64 (RHEL6.3 2.6.32-358.11.1.el6.x86_64) and when using:

我没有在linux x86_64(RHEL6.3 2.6.32-358.11.1.el6.x86_64)上看到perl-5.12.4的“make test”出现任何故障,并且在使用时:

strace -fe trace=lstat perl -e 'use File::Glob q{:glob};
                               print scalar bsd_glob(q{/var/log/*},GLOB_NOCHECK)'

I no longer see the lstat calls for each file in the dir. I don't mean to suggest that the perl tests for glob (File-Glob) are comprehensive (they are not), or that a change such as this will not break existing behaviour (this seems likely). As far as I can tell the code with this (g_l)stat call existed in original-bsd/lib/libc/gen/glob.c 24 years ago in 1990.

我不再在dir中看到每个文件的lstat调用。我并不是说建议对glob(File-Glob)的perl测试是全面的(它们不是),或者像这样的更改不会破坏现有行为(这似乎很可能)。据我所知,这个(g_l)stat调用的代码存在于原始-bsd / lib / libc / gen / glob.c 24年前的1990年。

Also see:

Chapter 6. Benchmarking Perl of "Mastering Perl" By brian d foy, Randal L. Schwartz contains a section on comparing code where code using glob() and opendir() is compared.

第6章“掌握Perl”的Perl标记作者:brian d foy,Randal L. Schwartz包含一个比较代码的部分,其中比较了使用glob()和opendir()的代码。

"future globs (was "UNIX mindset...")" in comp.unix.wizards from Dick Dunn in 1991.

1991年,来自Dick Dunn的comp.unix.wizards中的“未来的全球(是”UNIX心态......“)”。

Usenet newsgroup mod.sources "'Globbing' library routine (glob)" from Guido van Rossum in July 1986 - I don't see a reference to "stat" in this code.

1986年7月来自Guido van Rossum的Usenet新闻组mod.sources“'Globbing'库例程(glob)” - 我在这段代码中没有看到“stat”的引用。

#1