comment on

Tracking this stuff through the perl sources is a nightmare.

The -f is mapped to a function Perl_pp_ftis in opcode.h (for FileTestIs (a file) perhaps?).
Which is mapped to lib\core\embed.h:#define pp_ftis Perl_pp_ftis

Which is implemented in terms of my_stat() in pp_sys.c

PP(pp_ftis)
{
    I32 result = my_stat();
    dSP;
    if (result < 0)
    RETPUSHUNDEF;
    RETPUSHYES;
}
[download]

Which is mapped to embed.h:3209:#define my_stat() Perl_my_stat(aTHX)
Perl_my_stat() is implemented in doio.c in terms of PerlLIO_fstat()
Which is mapped to iperlsys.h:734:#define PerlLIO_fstat(fd, buf) Fstat((fd), (buf))
Which gets mapped to lib\core\dosish.h:133:#define Fstat(fd,bufptr) fstat((fd),(bufptr))
Which is a c-runtime api.
However, fstat() takes a file descriptor (fd), which implies an open file handle...Should have noticed that earlier. Track back to where the calls are not defined in terms of a file descriptor and were back at doio.c. Sure enough, follow the other path in Perl_my_stat()and we find it calls PerlLIO_stat()
Which maps to lib\core\iperlsys.h:739:#define PerlLIO_stat(name, buf) Stat((name), (buf))
Which is mapped to dosish.h:142:# define Stat(fname,bufptr) stat((fname),(bufptr))
Then you have to move over to the C-runtime headers, which I don't have for MSVC++ (as used by Active State), so I can't bore you with those details, but suffice it to say, stat() ends up getting mapped to _stat64() as AS build with large file support which means they need the version of stat that can handle filesizes >32-bit.

Dissassembling the code in MSVCRT.dll:_stat64 we find this

Disassembly of Function _stat64  (0x78018226)
;*********************************************************************
+***********
; *** _stat64 (456) ***
; SYM:_stat64
0x78018226: push     ebp                                
0x78018227: mov      ebp,esp                            
0x78018229: sub      esp,0x24c                          
0x7801822F: push     ebx                                
0x78018230: mov      ebx,dword ptr [ebp+0x8]            ; ARG:0x8
0x78018233: push     esi                                
0x78018234: push     edi                                
0x78018235: push     0x78034c00                         ; DATA:?*
0x7801823A: push     ebx                                
0x7801823B: call     0x7800edaa                         ; SYM:_mbspbrk
0x78018240: pop      ecx                                
0x78018241: test     eax,eax                            
0x78018243: pop      ecx                                
0x78018244: jnz      0x78018398                         ; (*+0x154) 
0x7801824A: cmp      byte ptr [ebx+0x1],0x3a            
0x7801824E: jnz      0x7801838e                         ; (*+0x140) 
0x78018254: mov      eax,dword ptr [ebx]                
0x78018256: test     al,al                              
0x78018258: jz       0x78018264                         ; (*+0xC) 
0x7801825A: cmp      byte ptr [ebx+0x2],0x0             
0x7801825E: jz       0x78018398                         ; (*+0x13A) 
0x78018264: movsx    al,al                              ; <==0x7801825
+8(*-0xC)
0x78018267: push     eax                                
0x78018268: call     0x7801eceb                         ; SYM:_mbctolo
+wer
0x7801826D: pop      ecx                                
0x7801826E: sub      eax,0x60                           
0x78018271: mov      dword ptr [ebp-0x4],eax            ; VAR:0x4; <==
+0x78018393(*+0x122)
0x78018274: lea      eax,dword ptr [ebp-0x148]          ; VAR:0x148
0x7801827A: push     eax                                
0x7801827B: push     ebx                                
0x7801827C: call     dword ptr [0x78033080]             ; EXT:KERNEL32
+.DLL!FindFirstFileA
0x78018282: cmp      eax,0xff                           
0x78018285: mov      dword ptr [ebp-0x8],eax            ; VAR:0x8
0x78018288: jnz      0x780183b1                         ; (*+0x129) 
0x7801828E: push     0x78034bfc                         ; DATA:./\
0x78018293: push     ebx                                
0x78018294: call     0x7800edaa                         ; SYM:_mbspbrk
0x78018299: pop      ecx                                
0x7801829A: test     eax,eax                            
0x7801829C: pop      ecx                                
0x7801829D: jz       0x78018398                         ; (*+0xFB) 
0x780182A3: push     0x104                              
0x780182A8: lea      eax,dword ptr [ebp-0x24c]          ; VAR:0x24
0x780182AE: push     ebx                                
0x780182AF: push     eax                                
0x780182B0: call     0x78017bbf                         ; SYM:_fullpat
+h
0x780182B5: mov      esi,eax                            
0x780182B7: xor      edi,edi                            
0x780182B9: add      esp,0xc                            
0x780182BC: cmp      esi,edi                            
0x780182BE: jz       0x78018398                         ; (*+0xDA) 
0x780182C4: push     esi                                
0x780182C5: call     0x78003a9f                         ; SYM:strlen
0x780182CA: cmp      eax,0x3                            
0x780182CD: pop      ecx                                
0x780182CE: jz       0x780182df                         ; (*+0x11) 
0x780182D0: push     esi                                
0x780182D1: call     0x7801874b                         
0x780182D6: test     eax,eax                            
0x780182D8: pop      ecx                                
0x780182D9: jz       0x78018398                         ; (*+0xBF) 
0x780182DF: push     esi                                ; <==0x780182C
+E(*-0x11)
0x780182E0: call     dword ptr [0x78033170]             ; EXT:KERNEL32
+.DLL!GetDriveTypeA
0x780182E6: cmp      eax,0x1                            
0x780182E9: jbe      0x78018398                         ; (*+0xAF) 
0x780182EF: and      byte ptr [ebp-0x11c],0x0           ; VAR:0x11
0x780182F6: mov      esi,dword ptr [ebp+0xc]            ; ARG:0x
0x780182F9: push     0xff                               
0x780182FB: push     edi                                
0x780182FC: push     edi                                
0x780182FD: push     edi                                
0x780182FE: push     0x1                                
0x78018300: push     0x1                                
0x78018302: push     0x7bc                              
0x78018307: mov      dword ptr [ebp-0x148],0x10         ; VAR:0x148
0x78018311: mov      dword ptr [ebp-0x12c],edi          ; VAR:0x12
0x78018317: mov      dword ptr [ebp-0x128],edi          ; VAR:0x128
0x7801831D: call     0x7802ab02                         
0x78018322: mov      dword ptr [esi+0x28],eax           
0x78018325: mov      dword ptr [esi+0x2c],edx           
0x78018328: mov      eax,dword ptr [esi+0x28]           
0x7801832B: mov      ecx,edx                            
0x7801832D: mov      dword ptr [esi+0x20],eax           
0x78018330: mov      dword ptr [esi+0x30],eax           
0x78018333: add      esp,0x1c                           
0x78018336: mov      dword ptr [esi+0x24],ecx           
0x78018339: mov      dword ptr [esi+0x34],ecx           
0x7801833C: push     ebx                                ; <==0x7801842
+E(*+0xF2)
0x7801833D: push     dword ptr [ebp-0x148]              ; VAR:0x148
0x78018343: call     0x78017ea1                         
0x78018348: pop      ecx                                
0x78018349: mov      word ptr [esi+0x6],ax              
0x7801834D: pop      ecx                                
0x7801834E: mov      word ptr [esi+0x8],0x1             
0x78018354: push     0x1                                
0x78018356: push     edi                                
0x78018357: push     edi                                
0x78018358: push     dword ptr [ebp-0x12c]              ; VAR:0x12
0x7801835E: call     0x78003e1a                         
0x78018363: mov      ecx,dword ptr [ebp-0x128]          ; VAR:0x128
0x78018369: xor      ebx,ebx                            
0x7801836B: add      eax,ecx                            
0x7801836D: mov      word ptr [esi+0x4],di              
0x78018371: mov      dword ptr [esi+0x18],eax           
0x78018374: mov      eax,dword ptr [ebp-0x4]            ; VAR:0x4
0x78018377: adc      edx,ebx                            
0x78018379: dec      eax                                
0x7801837A: mov      dword ptr [esi],eax                
0x7801837C: mov      dword ptr [esi+0x10],eax           
0x7801837F: mov      dword ptr [esi+0x1c],edx           
0x78018382: mov      word ptr [esi+0xc],di              
0x78018386: mov      word ptr [esi+0xa],di              
0x7801838A: xor      eax,eax                            
0x7801838C: jmp      0x780183ac                         ; (*+0x20) 
0x7801838E: call     0x78017a8f                         ; SYM:_getdriv
+e; <==0x7801824E(*-0x140)
0x78018393: jmp      0x78018271                         ; (*-0x122) 
0x78018398: call     0x7800c9ac                         ; SYM:_errno; 
+<==0x78018244(*-0x154), 0x7801829D(*-0xFB), 0x780182BE(*-0xDA), 0x780
+182D9(*-0xBF), 0x7801825E(*-0x13A), 0x780182E9(*-0xAF)
0x7801839D: push     0x2                                
0x7801839F: pop      esi                                
0x780183A0: mov      dword ptr [eax],esi                
0x780183A2: call     0x7800c9b5                         ; SYM:__doserr
+no
0x780183A7: mov      dword ptr [eax],esi                
0x780183A9: or       eax,0xff                           
0x780183AC: pop      edi                                ; <==0x7801838
+C(*-0x20)
0x780183AD: pop      esi                                
0x780183AE: pop      ebx                                
0x780183AF: leave                                       
0x780183B0: ret                                         
;*********************************************************************
+***********
[download]

The salient point here is the call to EXT:KERNEL32.DLL!FindFirstFileA.

You asked: ...why this is effectively performing a directory search in order to test one filename!..... And the answer goes something like this.

When you pass a filespec to stat() or one of its varients, in order to ask the os for information about the file, you need to get an OS 'handle' (an INODE) in unix terms) to that file. You can get one of these by various means, but if you aren't interested in opening the file, then the OS gives you a call to obtain that handle. In Win32 this is FindFirstFile(), I think the equivalent under unix is opendir or maybe it gets translated directly into (ioctl?) calls to the underlying filesystem.

Anyway, the point is that under normal circumstances, calling FFF with a non-wildcard filespec returns a structure containing (almost) all the information required to satisfy the stat() call.

typedef struct _WIN32_FIND_DATA {
  DWORD dwFileAttributes;
  FILETIME ftCreationTime;
  FILETIME ftLastAccessTime;
  FILETIME ftLastWriteTime;
  DWORD nFileSizeHigh;
  DWORD nFileSizeLow;
  DWORD dwReserved0;
  DWORD dwReserved1;
  TCHAR cFileName[MAX_PATH];
  TCHAR cAlternateFileName[14];
} WIN32_FIND_DATA, *PWIN32_FIND_DATA;
[download]

Whilst you may not thinkof stat() as doing a "directory search", it has to have the filesystem search to find the information to fulfil the stat() call, which on unix is in the INODE and so a search is being done, it's just that the API name doesn't reflect this.

The fact that your filespec contains some adornments used for determining the filemode is a Perl thing and not the OS's problem.

That these conflict with an undocumented feature within the OS is ...erm.. unfortunate! I guess that LW and MS came to the same conclusion that '<' & '>' are good candidates for using as meta characters as most sane people are unlikely to embed these in their filenames as they would conflict with their use as redirection metacharacters by CLIs.

In the final analysis, you would have to strip Perls two-arg open metacharacters from the filespec before you passed them to stat(), whichever OS you are on!

Examine what is said, not who speaks.

"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller
If I understand your problem, I can solve it! Of course, the same can be said for you.

In reply to Re: Re: Re: Re: Re: Unexpected file test (-f) result on Windows by BrowserUk
in thread Unexpected file test (-f) result on Windows by DaveH

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