true from (-e "") on Windoze

[CarolinaPerler]

On UNIX/Linux/Mac, this:

$file = '""';
if (-e $file) { print "Yep\n"; } else {print "Nope\n"; }

prints 'Nope'.
On Windoze it prints 'Yep.'

What am I missing. There is not path/file of '""' on the system, neither now no ever.

Slightly annoying that it appears I'm going to have to sniff the path/file string to see if it is an empty pair of double quotes. (I don't control what is feeding me empty double quotes as a path/filename string.)

I'm not a Windows Guru. On windoze, is the empty double quote string used for some special purpose? Why would the Perl -e test think it is a valid path/file that actually exists on the system? Thanks

[BrowserUk]

The quote " character is illegal in Windows filenames. Therefore, what you are passing to the OS is taken as the empty string.

And when you search for the empty string, dir "", you get everything.

You are effectively asking, is there anything in the current directory. Which will always be true.

[ikegami]

The file name is illegal, but no, we won't return an error! yuck.

Is there a system call that can be called instead of C's stat?

[BrowserUk]

The file name is illegal, but no, we won't return an error! yuck.

Not sure why "yuck"?

Either, it should be treated as illegal and return "The system cannot find the file specified",

or it is a valid alias for CWD and should do what it now does.

I can't see what other option there is?

Is there a system call that can be called instead of C's stat?

I'm not sure what that would achieve?

Most of the values returned by stat that actually have any meaning on NTFS, are available via GetFileAttributesEx().

But be aware, Win32.c:Win32_stat() already calls this (but only if _stat()/_stat64() fail??), along with several others (GetFileAttributesA()/GetVolumeInformationA()/GetFileInformationByHandle()) in order to fix-up what they see as bugs.

[syphilis]

The quote " character is illegal in Windows filenames

Therefore the OP should get the error:

The filename, directory name, or volume label syntax is incorrect.

That's the same error as produced by dir "\"\""

For mine, it's a bug that perl behaves the way it does - and I think the OP should submit a bug report by running perlbug and following the prompts.

Cheers,
Rob

[BrowserUk]

As I showed in Re^3: true from (-e "") on Windoze (" is an illegal filename character, it is the MS CRT stat (and I believe the Winapi function(s) that underlies it), that chooses to treat a filename passed as '""' as meaning 'the current directory'.

As such, I don't think that it can be blamed on Perl.

That's not to say that Perl might not choose to prevent it by detecting it and failing, before passing it through to stat, and so regularise the cross-platform Perl behaviour.

But, it would be 'correcting' for a bug -- if you wish to call it that -- in the CRT, not Perl per se.

I also suspect that the 'bug' probably goes all the way back to MSDOS, where it was considered a useful behaviour.

[Anonymous Monk]

$ dir "\"\""
The network path was not found.

$ echo %ERRORLEVEL%
1

[afoken]

And when you search for the empty string, dir "", you get everything.

dir is not stat().

The quote " character is illegal in Windows filenames. Therefore, what you are passing to the OS is taken as the empty string.

No. If it would, stat() in the C example would return 0 (success), not -1 (error).

You are effectively asking, is there anything in the current directory. Which will always be true.

Wrong conclusion.

Alexander

[BrowserUk]

Sorry, but you are wrong. Here is the proof:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>

int main( int argc, char **argv ) {
    struct _stat buf1, buf2;
    char *file = "\"\"";

    printf( "for %s; stat returned: %d\n", file, _stat( file, &buf1 ) 
+);

    printf(
        "gid: %d\natime:%I64x\nctime:%I64x\ndrive:%d\n"
        "inode:%d\nmode:%x\nmtime:%I64x\nnlink:%d\nrdev:%d\n"
        "size:%d\nuid:%d\n",
        buf1.st_gid, buf1.st_atime, buf1.st_ctime, buf1.st_dev,
        buf1.st_ino, buf1.st_mode, buf1.st_mtime, buf1.st_nlink, buf1.
+st_rdev,
        buf1.st_size, buf1.st_uid
    );

    printf( "\nFor %s; stat returned: %d\n", argv[1], _stat( argv[1], 
+&buf2 ) );

    printf(
        "gid: %d\natime:%I64x\nctime:%I64x\ndrive:%d\n"
        "inode:%d\nmode:%x\nmtime:%I64x\nnlink:%d\nrdev:%d\n"
        "size:%d\nuid:%d\n",
        buf2.st_gid, buf2.st_atime, buf2.st_ctime, buf2.st_dev,
        buf2.st_ino, buf2.st_mode, buf2.st_mtime, buf2.st_nlink, buf2.
+st_rdev,
        buf2.st_size, buf2.st_uid
    );
    return 1;
}

That code first stats the filename '""'; then it stats the pathname passed from the command line in argv1.

Run passing the path of the current directory, both sets of stats are identical:

C:\test>stat c:\test
for ""; stat returned: 0
gid: 0
atime:4ff203c6
ctime:49bba448
drive:2
inode:0
mode:41ff
mtime:4ff203c6
nlink:1
rdev:2
size:0
uid:0

For c:\test; stat returned: 0
gid: 0
atime:4ff203c6
ctime:49bba448
drive:2
inode:0
mode:41ff
mtime:4ff203c6
nlink:1
rdev:2
size:0
uid:0

Explain that in any way other than '""' is being taken to mean 'the current directory'?

[Jenda]

It's not just two doublequotes. Just one doublequote, three doublequotes, ... seems any number of doublequotes work. Considering the fact that a doublequote is an illegal character in file names in Windows ...

[afoken]

It's not just two doublequotes. Just one doublequote, three doublequotes, ... seems any number of doublequotes work.

... but not in C code, only in perl.

Considering the fact that a doublequote is an illegal character in file names in Windows ...

... there can be no file or directory with such a name, so stat() should fail, either with "file not found" or with "invalid file name". But it should not stat() the current directory instead.

Alexander

[afoken]

Looks like a bug to me.

Linux:

>uname -a
Linux enterprise 2.6.37.6-foken #2 SMP Sun Aug 14 02:20:59 CEST 2011 x
+86_64 AMD Athlon(tm) II Neo N36L Dual-Core Processor AuthenticAMD GNU
+/Linux

>perl -E '$file=q[""]; say (-e($file) ? "yes" : "no")'
no

>perl -V
Summary of my perl5 (revision 5 version 12 subversion 3) configuration
+:

  Platform:
    osname=linux, osvers=2.6.35.10, archname=x86_64-linux-thread-multi
    uname='linux midas64 2.6.35.10 #2 smp thu jan 6 19:06:19 cst 2011 
+x86_64 amd athlon(tm) ii x2 235e processor authenticamd gnulinux '
    config_args='-de -Dprefix=/usr -Dvendorprefix=/usr -Dcccdlflags=-f
+PIC -Dinstallprefix=/usr -Dlibpth=/usr/local/lib64 /usr/lib64 /lib64 
+-Doptimize=-O2 -fPIC -Dusethreads -Duseithreads -Dpager=/usr/bin/less
+ -isr -Dinc_version_list=5.12.2 5.12.1 5.12.0 5.10.1 5.10.0 5.8.8 5.8
+.7 5.8.6 5.8.5 5.8.4 5.8.3 5.8.2 5.8.1 5.8.0 -Darchname=x86_64-linux'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=und
+ef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing
+ -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_
+FILE_OFFSET_BITS=64',
    optimize='-O2 -fPIC',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -f
+stack-protector -I/usr/local/include'
    ccversion='', gccversion='4.5.2', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+6
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector'
    libpth=/usr/local/lib64 /usr/lib64 /lib64
    libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=/lib64/libc-2.12.2.so, so=so, useshrplib=false, libperl=libpe
+rl.a
    gnulibc_version='2.12.2'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -fPIC -fstack-protector
+'


Characteristics of this binary (from libperl):
  Compile-time options: MULTIPLICITY PERL_DONT_CREATE_GVSV
                        PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP USE_64_
+BIT_ALL
                        USE_64_BIT_INT USE_ITHREADS USE_LARGE_FILES
                        USE_PERLIO USE_PERL_ATOF USE_REENTRANT_API
  Built under linux
  Compiled at Jan 26 2011 12:39:46
  %ENV:
    PERL_UNICODE="SDL"
  @INC:
    /usr/lib64/perl5/site_perl/5.12.3/x86_64-linux-thread-multi
    /usr/lib64/perl5/site_perl/5.12.3
    /usr/lib64/perl5/vendor_perl/5.12.3/x86_64-linux-thread-multi
    /usr/lib64/perl5/vendor_perl/5.12.3
    /usr/lib64/perl5/5.12.3/x86_64-linux-thread-multi
    /usr/lib64/perl5/5.12.3
    /usr/lib64/perl5/site_perl
    /usr/lib64/perl5/vendor_perl
    .

Windows:

C:\Users\alex>perl -E "$file=chr(34).chr(34); say $file.' '.(-e($file)
+ ? 'yes' :  'no')"
"" yes

C:\Users\alex>ver

Microsoft Windows [Version 6.1.7601]

C:\Users\alex>dir
 Volume in drive C is System
 Volume Serial Number is B663-2E5B

 Directory of C:\Users\alex

24.06.2012  19:12    <DIR>          .
24.06.2012  19:12    <DIR>          ..
25.05.2012  23:46    <DIR>          .gegl-0.0
24.06.2012  19:21    <DIR>          .gimp-2.6
24.06.2012  19:12             6.262 .recently-used.xbel
28.05.2012  14:19    <DIR>          .thumbnails
06.05.2012  23:44    <DIR>          Contacts
24.06.2012  19:12    <DIR>          Desktop
24.06.2012  19:41    <DIR>          Documents
01.07.2012  19:22    <DIR>          Downloads
24.06.2012  19:32    <DIR>          Favorites
06.05.2012  23:44    <DIR>          Links
16.06.2012  12:54    <DIR>          Music
25.05.2012  23:50    <DIR>          Pictures
06.05.2012  23:44    <DIR>          Saved Games
06.05.2012  23:44    <DIR>          Searches
06.05.2012  23:44    <DIR>          Videos
15.06.2012  21:05    <DIR>          Virtual Machines
               1 File(s)          6.262 bytes
              17 Dir(s)  11.921.534.976 bytes free

C:\Users\alex>perl -V
Summary of my perl5 (revision 5 version 14 subversion 2) configuration
+:

  Platform:
    osname=MSWin32, osvers=4.0, archname=MSWin32-x64-multi-thread
    uname='Win32 strawberryperl 5.14.2.1 #1 Tue Nov 22 22:40:59 2011 x
+64'
    config_args='undef'
    hint=recommended, useposix=true, d_sigaction=undef
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=und
+ef
    use64bitint=define, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags =' -s -O2 -DWIN32 -DWIN64 -DCONSERVATIVE  -DPERL
+_TEXTMODE_SCRIPTS -DUSE_SITECUSTOMIZE -DPERL_IMPLICIT_CONTEXT -DPERL_
+IMPLICIT_SYS -fno-strict-aliasing -mms-bitfields',
    optimize='-s -O2',
    cppflags='-DWIN32'
    ccversion='', gccversion='4.4.7', gccosandvers=''
    intsize=4, longsize=4, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+2
    ivtype='long long', ivsize=8, nvtype='double', nvsize=8, Off_t='lo
+ng long', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='g++', ldflags ='-s -L"C:\strawberry\perl\lib\CORE" -L"C:\straw
+berry\c\lib"'
    libpth=C:\strawberry\c\lib C:\strawberry\c\x86_64-w64-mingw32\lib
    libs=-lmoldname -lkernel32 -luser32 -lgdi32 -lwinspool -lcomdlg32 
+-ladvapi32 -lshell32 -lole32 -loleaut32 -lnetapi32 -luuid -lws2_32 -l
+mpr -lwinmm -lversion -lodbc32 -lodbccp32 -lcomctl32
    perllibs=-lmoldname -lkernel32 -luser32 -lgdi32 -lwinspool -lcomdl
+g32 -ladvapi32 -lshell32 -lole32 -loleaut32 -lnetapi32 -luuid -lws2_3
+2 -lmpr -lwinmm -lversion -lodbc32 -lodbccp32 -lcomctl32
    libc=, so=dll, useshrplib=true, libperl=libperl514.a
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_win32.xs, dlext=dll, d_dlsymun=undef, ccdlflags=' '
    cccdlflags=' ', lddlflags='-mdll -s -L"C:\strawberry\perl\lib\CORE
+" -L"C:\strawberry\c\lib"'


Characteristics of this binary (from libperl):
  Compile-time options: MULTIPLICITY PERL_DONT_CREATE_GVSV
                        PERL_IMPLICIT_CONTEXT PERL_IMPLICIT_SYS
                        PERL_MALLOC_WRAP PERL_PRESERVE_IVUV PL_OP_SLAB
+_ALLOC
                        USE_64_BIT_INT USE_ITHREADS USE_LARGE_FILES
                        USE_PERLIO USE_PERL_ATOF USE_SITECUSTOMIZE
  Built under MSWin32
  Compiled at Nov 22 2011 22:53:05
  %ENV:
    PERL_JSON_BACKEND="JSON::XS"
    PERL_YAML_BACKEND="YAML"
  @INC:
    C:/strawberry/perl/site/lib
    C:/strawberry/perl/vendor/lib
    C:/strawberry/perl/lib
    .

C:\Users\alex>

Even shorter:

C:\Users\alex>perl -E "stat(chr(34).chr(34)) or die $!; say 'huh?'"
huh?

C:\Users\alex>

vs.

>perl -E 'stat(q[""]) or die $!; say "huh?"'
No such file or directory at -e line 1.

>

If stat is successful, what is in stat()s return value?

C:\Users\alex>perl -MData::Dumper -E "@a=stat(chr(34).chr(34)) or die 
+$!; say Du
mper(\@a)"
$VAR1 = [
          2,             # device
          0,             # inode
          16895,         # mode = 0x41FF = 040777
          1,             # nlink
          0,             # uid
          0,             # gid
          2,             # rdev
          0,             # size
          1340557931,    # atime
          1340557931,    # mtime
          1336337436,    # ctime
          '',            # blocksize
          ''             # blocks
        ];


C:\Users\alex>

Mode 0777 happens on Windows only for executables (by extension) and for directories. The bit 040000 looks like the directory flag. This fits the picture, because there is no executable extension in the file name.

Maybe some routine burried deep inside Perl, MinGW or Windows unquotes filenames? Let's look at the stat() output for "." and "..":

C:\Users\alex>perl -MData::Dumper -E "for $x (chr(34).chr(34),'.','..'
+) { @a=stat($x); say Dumper(\@a) }"
$VAR1 = [
          2,
          0,
          16895,
          1,
          0,
          0,
          2,
          0,
          1340557931,
          1340557931,
          1336337436,
          '',
          ''
        ];

$VAR1 = [
          2,
          0,
          16895,
          1,
          0,
          0,
          2,
          0,
          1340557931,
          1340557931,
          1336337436,
          '',
          ''
        ];

$VAR1 = [
          2,
          0,
          16749,
          1,
          0,
          0,
          2,
          0,
          1339842184,
          1339842184,
          1247541608,
          '',
          ''
        ];


C:\Users\alex>

Exact match for ".". Are quotes removed automatically?

C:\Users\alex>perl -MData::Dumper -E "@a=stat(chr(34).'Desktop'.chr(34
+)); say Dumper(\@a)"
$VAR1 = [];


C:\Users\alex>perl -MData::Dumper -E "@a=stat(''); say Dumper(\@a)"
$VAR1 = [];


C:\Users\alex>perl -MData::Dumper -E "@a=stat(chr(34).'..'.chr(34)); s
+ay Dumper(\@a)"
$VAR1 = [];


C:\Users\alex>perl -MData::Dumper -E "@a=stat(chr(34).'.'.chr(34)); sa
+y Dumper(\@a)"
$VAR1 = [];


C:\Users\alex>

No. I have no clue why '""' is treated like '.' on Windows.

What happens when I call stat() from C/MinGW?

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

int main(int argc, char ** argv)
{
    struct stat st;

    printf("stat(\"\") = %i\n",stat("\"\"",&st));
    return 0;
}

X:\>gcc -o stattest.exe stattest.c

X:\>stattest
stat("") = -1

X:\>

So, it's very likely neither Windows nor MinGW, so it must be Perl.

Alexander

[frozenwithjoy]

Does it work as expected if you type in some random letters between the quotes? I don't use Windows, but one way you could get around this is something like:

if ( $file and -e $file ) { say "yep"; }
else { say "nope"; }

[CountZero]

That won't work. Empty double quotes in a string are considered "true" by Perl.

[frozenwithjoy]

Works fine for me. Also, here is a handy table for this sort of thing: "Truth tests for different values" on True or False? A Quick Reference Guide. defined $file, however, would be true for an empty string.

edit: Oops, I didn't catch that there were quotes inside quotes...

[CarolinaPerler]

if ($file) returns true, also because the variable has content, two double quotes. I think I'm going to have to just check to see if my $file variable contains a pair of double quotes and only a pair of double quotes. 'Seem like a hack, though. 'Seems like the '-e' test operator would return false on this case.

That's what makes me wonder if Windoze actually uses the empty double quotes as some kind of file system object/entity. That would make the '-e' test think the empty-double-quote-thing was real and existed..... Don't know that much about the various file system types and how Perl on Windows handles them.

[BillKSmith]

Windows uses double quotes to solve a problem caused by file (or directory) names which contain spaces.

dir "C:\Program Files\" Works as intended

dir  C:\Program Files\ File not found

dir "" Displays current directory

[frozenwithjoy]

OK, how about this? (I've tested and it is working correctly for $file = '""'; on OS X.)

for ($file) {
    say "nope (empty quotes)" when /""/;
    say "yep" when -e $file;
    default { say "nope (doesn't exist)"}
}

[ww]

I think you're misinterpreting comments preceding Re^2: true from (-e "") on Windoze; I think the fact that the VALUE of $file is -- per se -- true is borking your expectations.

I don't recall any version of windows accepting "" or '""' or """" as a filename or filename element ...or any of the DOS/doze FS using "", et al, for anything.

[frozenwithjoy]

Ya, I didn't catch that they were quotes within quotes. Out of curiosity, why/how is that happening?

[CarolinaPerler]

Yes, it does. If I put anything between the quotes, I get the expected results. It is just the empty double quotes that unexpectedly returns true from '-e'.

[monsoon]

$file = '""';
if (-e $file && !-d $file) { print "Yep\n"; } else {print "Nope\n"; }

Won't work of course if the file list can contain directories.

[scorpio17]

How about this:

$file = '""';
if ( -e $file && -f $file ) { 
  print "Yes\n"; 
} else {
  print "No\n"; 
}

[monsoon]

I think -f rules out too much, named pipes for example. It all depends on what kind of files the list can contain.

[BrowserUk]

FTR: This code shows that the behaviour of treating the filename '""' as an alias for CWD, is an inherent part of the Windows API:

#include <windows.h>
#include <stdio.h>

int main( int argc, char **argv ) {
    char *file = "\"\"";
    char buf[ 1024 ];

    GetFullPathName( file, 1024, buf, NULL );
    printf( "%s -> %s\n", file,  buf );

    return 1;
}

Build and run:

C:\test>cl /W3 GetFullPathName.c
Microsoft (R) C/C++ Optimizing Compiler Version 15.00.21022.08 for x64
Copyright (C) Microsoft Corporation.  All rights reserved.

GetFullPathName.c
Microsoft (R) Incremental Linker Version 9.00.21022.08
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:GetFullPathName.exe
GetFullPathName.obj

C:\test>GetFullPathName
"" -> C:\test\""

And exposed to Perl directly via:

C:\test>perl -MWin32 -E"say Win32::GetFullPathName( '\"\"' )"
C:\test\""