Specific features of the Cygwin port


perlcygwin − Perl for Cygwin


This document will help you configure, make, test and install Perl on Cygwin. This document also describes features of Cygwin that will affect how Perl behaves at runtime.

NOTE: There are pre-built Perl packages available for Cygwin and a version of Perl is provided in the normal Cygwin install. If you do not need to customize the configuration, consider using one of those packages.


Cygwin = GNU+Cygnus+Windows (Don’t leave UNIX without it)
The Cygwin tools are ports of the popular GNU development tools for Win32 platforms. They run thanks to the Cygwin library which provides the UNIX system calls and environment these programs expect. More information about this project can be found at:


A recent net or commercial release of Cygwin is required.

At the time this document was last updated, Cygwin 1.7.16 was current.

Cygwin Configuration
While building Perl some changes may be necessary to your Cygwin setup so that Perl builds cleanly. These changes are not required for normal Perl usage.

NOTE: The binaries that are built will run on all Win32 versions. They do not depend on your host system (WinXP/Win2K/Win7) or your Cygwin configuration (binary/text mounts, cvgserver). The only dependencies come from hard-coded pathnames like /usr/local. However, your host system and Cygwin configuration will affect Perl’s runtime behavior (see " TEST" ).


Set the "PATH" environment variable so that Configure finds the Cygwin versions of programs. Any not-needed Windows directories should be removed or moved to the end of your "PATH".


If you do not have nroff (which is part of the groff package), Configure will not prompt you to install man pages.


The default options gathered by Configure with the assistance of hints/ will build a Perl that supports dynamic loading (which requires a shared cygperl5_16.dll).

This will run Configure and keep a record:

  ./Configure 2>&1 | tee log.configure

If you are willing to accept all the defaults run Configure with −de. However, several useful customizations are available.

Stripping Perl Binaries on Cygwin
It is possible to strip the EXEs and DLLs created by the build process. The resulting binaries will be significantly smaller. If you want the binaries to be stripped, you can either add a −s option when Configure prompts you,

   Any additional ld flags (NOT including libraries)? [none] −s
  Any special flags to pass to g++ to create a dynamically loaded library?
  [none] −s
  Any special flags to pass to gcc to use dynamic linking? [none] −s

or you can edit hints/ and uncomment the relevant variables near the end of the file.

Optional Libraries for Perl on Cygwin
Several Perl functions and modules depend on the existence of some optional libraries. Configure will find them if they are installed in one of the directories listed as being used for library searches. Pre-built packages for most of these are available from the Cygwin installer.


The crypt package distributed with Cygwin is a Linux compatible 56−bit DES crypt port by Corinna Vinschen.

Alternatively, the crypt libraries in GNU libc have been ported to Cygwin.

"−lgdbm_compat" ("use GDBM_File")

GDBM is available for Cygwin.

NOTE: The GDBM library only works on NTFS partitions.

"−ldb" ("use DB_File")

BerkeleyDB is available for Cygwin.

NOTE: The BerkeleyDB library only completely works on NTFS partitions.

"cygserver" ("use IPC::SysV")

A port of SysV IPC is available for Cygwin.

NOTE: This has not been extensively tested. In particular, "d_semctl_semun" is undefined because it fails a Configure test and on Win9x the shm*() functions seem to hang. It also creates a compile time dependency because perl.h includes <sys/ipc.h> and <sys/sem.h> (which will be required in the future when compiling CPAN modules). CURRENTLY NOT SUPPORTED !


Included with the standard Cygwin netrelease is the inetutils package which includes libutil.a.

Configure-time Options for Perl on Cygwin
The INSTALL document describes several Configure-time options. Some of these will work with Cygwin, others are not yet possible. Also, some of these are experimental. You can either select an option when Configure prompts you or you can define (undefine) symbols on the command line.


Undefining this symbol forces Perl to be compiled statically.


By default Perl does not use the "malloc()" included with the Perl source, because it was slower and not entirely thread-safe. If you want to force Perl to build with the old −Dusemymalloc define this.


Undefining this symbol disables the PerlIO abstraction. PerlIO is now the default; it is not recommended to disable PerlIO.


Multiplicity is required when embedding Perl in a C program and using more than one interpreter instance. This is only required when you build a not-threaded perl with "−Uuseithreads".


By default Perl uses 64 bit integers. If you want to use smaller 32 bit integers, define this symbol.


gcc supports long doubles (12 bytes). However, several additional long double math functions are necessary to use them within Perl ({atan2, cos, exp, floor, fmod, frexp, isnan, log, modf, pow, sin, sqrt}l, strtold). These are not yet available with newlib, the Cygwin libc.


Define this symbol if you want not-threaded faster perl.


Cygwin uses 64−bit integers for internal size and position calculations, this will be correctly detected and defined by Configure.


Use this to build perl outside of the source tree. Details can be found in the INSTALL document. This is the recommended way to build perl from sources.

Suspicious Warnings on Cygwin
You may see some messages during Configure that seem suspicious.

Win9x and "d_eofnblk"

Win9x does not correctly report "EOF" with a non-blocking read on a closed pipe. You will see the following messages:

  But it also returns −1 to signal EOF, so be careful!
  WARNING: you can't distinguish between EOF and no data!
  *** WHOA THERE!!! ***
      The recommended value for $d_eofnblk on this machine was "define"!
      Keep the recommended value? [y]

At least for consistency with WinNT, you should keep the recommended value.

Compiler/Preprocessor defines

The following error occurs because of the Cygwin "#define" of "_LONG_DOUBLE":

  Guessing which symbols your C compiler and preprocessor define...
  try.c:<line#>: missing binary operator

This failure does not seem to cause any problems. With older gcc versions, "parse error" is reported instead of "missing binary operator".


Simply run make and wait:

  make 2>&1 | tee log.make


There are two steps to running the test suite:

  make test 2>&1 | tee log.make−test
  cd t; ./perl harness 2>&1 | tee ../log.harness

The same tests are run both times, but more information is provided when running as "./perl harness".

Test results vary depending on your host system and your Cygwin configuration. If a test can pass in some Cygwin setup, it is always attempted and explainable test failures are documented. It is possible for Perl to pass all the tests, but it is more likely that some tests will fail for one of the reasons listed below.

File Permissions on Cygwin
UNIX file permissions are based on sets of mode bits for {read,write,execute} for each {user,group,other}. By default Cygwin only tracks the Win32 read-only attribute represented as the UNIX file user write bit (files are always readable, files are executable if they have a .{com,bat,exe} extension or begin with "#!", directories are always readable and executable). On WinNT with the ntea "CYGWIN" setting, the additional mode bits are stored as extended file attributes. On WinNT with the default ntsec "CYGWIN" setting, permissions use the standard WinNT security descriptors and access control lists. Without one of these options, these tests will fail (listing not updated yet):

  Failed Test           List of failed
  io/fs.t               5, 7, 9−10
  lib/anydbm.t          2
  lib/db−btree.t        20
  lib/db−hash.t         16
  lib/db−recno.t        18
  lib/gdbm.t            2
  lib/ndbm.t            2
  lib/odbm.t            2
  lib/sdbm.t            2
    op/stat.t                         9, 20 (.tmp not an executable extension)

NDBM_File and ODBM_File do not work on FAT filesystems
Do not use NDBM_File or ODBM_File on FAT filesystem. They can be built on a FAT filesystem, but many tests will fail:

 ../ext/NDBM_File/ndbm.t       13  3328    71   59  83.10%  1−2 4 16−71
 ../ext/ODBM_File/odbm.t      255 65280    ??   ??       %  ??
 ../lib/AnyDBM_File.t           2   512    12    2  16.67%  1 4
 ../lib/Memoize/t/errors.t      0   139    11    5  45.45%  7−11
 ../lib/Memoize/t/tie_ndbm.t   13  3328     4    4 100.00%  1−4
 run/fresh_perl.t                          97    1   1.03%  91

If you intend to run only on FAT (or if using AnyDBM_File on FAT ), run Configure with the −Ui_ndbm and −Ui_dbm options to prevent NDBM_File and ODBM_File being built.

With NTFS (and no CYGWIN=nontsec), there should be no problems even if perl was built on FAT.

"fork()" failures in io_* tests
A "fork()" failure may result in the following tests failing:


See comment on fork in "Miscellaneous" below.

Specific features of the Cygwin port

Script Portability on Cygwin
Cygwin does an outstanding job of providing UNIX-like semantics on top of Win32 systems. However, in addition to the items noted above, there are some differences that you should know about. This is a very brief guide to portability, more information can be found in the Cygwin documentation.


Cygwin pathnames are separated by forward (/) slashes, Universal Naming Codes (//UNC) are also supported Since cygwin−1.7 non-POSIX pathnames are discouraged. Names may contain all printable characters.

File names are case insensitive, but case preserving. A pathname that contains a backslash or drive letter is a Win32 pathname, and not subject to the translations applied to POSIX style pathnames, but cygwin will warn you, so better convert them to POSIX.

For conversion we have "Cygwin::win_to_posix_path()" and "Cygwin::posix_to_win_path()".

Since cygwin−1.7 pathnames are UTF−8 encoded.


Since cygwin−1.7 textmounts are deprecated and strongly discouraged.

When a file is opened it is in either text or binary mode. In text mode a file is subject to CR/LF/Ctrl−Z translations. With Cygwin, the default mode for an "open()" is determined by the mode of the mount that underlies the file. See "Cygwin::is_binmount"(). Perl provides a "binmode()" function to set binary mode on files that otherwise would be treated as text. "sysopen()" with the "O_TEXT" flag sets text mode on files that otherwise would be treated as binary:

       sysopen(FOO, "bar", O_WRONLY|O_CREAT|O_TEXT)

"lseek()", "tell()" and "sysseek()" only work with files opened in binary mode.

The text/binary issue is covered at length in the Cygwin documentation.


PerlIO overrides the default Cygwin Text/Binary behaviour. A file will always be treated as binary, regardless of the mode of the mount it lives on, just like it is in UNIX. So CR/LF translation needs to be requested in either the "open()" call like this:

   open(FH, ">:crlf", "out.txt");

which will do conversion from LF to CR/LF on the output, or in the environment settings (add this to your .bashrc):

  export PERLIO=crlf

which will pull in the crlf PerlIO layer which does LF − > CRLF conversion on every output generated by perl.


The Cygwin "stat()", "lstat()" and "readlink()" functions make the .exe extension transparent by looking for foo.exe when you ask for foo (unless a foo also exists). Cygwin does not require a .exe extension, but gcc adds it automatically when building a program. However, when accessing an executable as a normal file (e.g., cp in a makefile) the .exe is not transparent. The install program included with Cygwin automatically appends a .exe when necessary.

Cygwin vs. Windows process ids

Cygwin processes have their own pid, which is different from the underlying windows pid. Most posix compliant Proc functions expect the cygwin pid, but several Win32::Process functions expect the winpid. E.g. $$ is the cygwin pid of /usr/bin/perl, which is not the winpid. Use "Cygwin::pid_to_winpid()" and "Cygwin::winpid_to_pid()" to translate between them.

Cygwin vs. Windows errors

Under Cygwin, $^E is the same as $!. When using Win32 API Functions, use "Win32::GetLastError()" to get the last Windows error.

rebase errors on fork or system

Using "fork()" or "system()" out to another perl after loading multiple dlls may result on a DLL baseaddress conflict. The internal cygwin error looks like like the following:

  0 [main] perl 8916 child_info_fork::abort: data segment start: parent
    (0xC1A000) != child(0xA6A000)


  183 [main] perl 3588 C:\cygwin in\perl.exe: *** fatal error − unable to remap
    C:\cygwin in\cygsvn_subr−1−0.dll to same address as parent(0x6FB30000) != 0x6FE60000
  46 [main] perl 3488 fork: child 3588 − died waiting for dll loading, errno11

See <−nochunks.html#faq.using.fixing−fork−failures> It helps if not too many DLLs are loaded in memory so the available address space is larger, e.g. stopping the MS Internet Explorer might help.

Use the perlrebase or rebase utilities to resolve the conflicting dll addresses. The rebase package is included in the Cygwin setup. Use setup.exe from <> to install it.

1. kill all perl processes and run "perlrebase" or

2. kill all cygwin processes and services, start dash from cmd.exe and run "rebaseall".


On WinNT "chown()" can change a file’s user and group IDs. On Win9x "chown()" is a no-op, although this is appropriate since there is no security model.


File locking using the "F_GETLK" command to "fcntl()" is a stub that returns "ENOSYS".

Win9x can not "rename()" an open file (although WinNT can).

The Cygwin "chroot()" implementation has holes (it can not restrict file access by native Win32 programs).

Inplace editing "perl −i" of files doesn’t work without doing a backup of the file being edited "perl −i.bak" because of windowish restrictions, therefore Perl adds the suffix ".bak" automatically if you use "perl −i" without specifying a backup extension.

Prebuilt methods:

Returns the current working directory.


Translates a cygwin pid to the corresponding Windows pid (which may or may not be the same).


Translates a Windows pid to the corresponding cygwin pid (if any).


Translates a Windows path to the corresponding cygwin path respecting the current mount points. With a second non-null argument returns an absolute path. Double-byte characters will not be translated.


Translates a cygwin path to the corresponding cygwin path respecting the current mount points. With a second non-null argument returns an absolute path. Double-byte characters will not be translated.


Returns an array of [mnt_dir, mnt_fsname, mnt_type, mnt_opts].

   perl −e 'for $i (Cygwin::mount_table) {print join(" ",@$i),"\n";}'
  /bin c:\cygwin in system binmode,cygexec
  /usr/bin c:\cygwin in system binmode
  /usr/lib c:\cygwin\lib system binmode
  / c:\cygwin system binmode
  /cygdrive/c c: system binmode,noumount
  /cygdrive/d d: system binmode,noumount
  /cygdrive/e e: system binmode,noumount


Returns the mount type and flags for a specified mount point. A comma-separated string of mntent−>mnt_type (always "system" or "user"), then the mntent−>mnt_opts, where the first is always "binmode" or "textmode".


If the argument is "/cygdrive", then just the volume mount settings, and the cygdrive mount prefix are returned.

User mounts override system mounts.

  $ perl −e 'print Cygwin::mount_flags "/usr/bin"'
  $ perl −e 'print Cygwin::mount_flags "/cygdrive"'


Returns true if the given cygwin path is binary mounted, false if the path is mounted in textmode.


Cygwin does not initialize all original Win32 environment variables. See the bottom of this page <−ug−net/setup−env.html> for "Restricted Win32 environment".

Certain Win32 programs called from cygwin programs might need some environment variable, such as e.g. ADODB needs %COMMONPROGRAMFILES%. Call Cygwin::sync_winenv() to copy all Win32 environment variables to your process and note that cygwin will warn on every encounter of non-POSIX paths.


This will install Perl, including man pages.

  make install 2>&1 | tee log.make−install

NOTE: If "STDERR" is redirected "make install" will not prompt you to install perl into /usr/bin.

You may need to be Administrator to run "make install". If you are not, you must have write access to the directories in question.

Information on installing the Perl documentation in HTML format can be found in the INSTALL document.


These are the files in the Perl release that contain references to Cygwin. These very brief notes attempt to explain the reason for all conditional code. Hopefully, keeping this up to date will allow the Cygwin port to be kept as clean as possible.

  pod/perl.pod pod/perlport.pod pod/perlfaq3.pod
  pod/perldelta.pod pod/perl5004delta.pod pod/perl56delta.pod
  pod/perl561delta.pod pod/perl570delta.pod pod/perl572delta.pod
  pod/perl573delta.pod pod/perl58delta.pod pod/perl581delta.pod
  pod/perl590delta.pod pod/perlhist.pod pod/perlmodlib.pod
  pod/perltoc.pod Porting/Glossary pod/perlgit.pod
  dist/Cwd/Changes ext/Compress−Raw−Zlib/Changes
  ext/Compress−Raw−Zlib/README ext/Compress−Zlib/Changes
  ext/DB_File/Changes ext/Encode/Changes ext/Sys−Syslog/Changes
  ext/Time−HiRes/Changes ext/Win32API−File/Changes lib/CGI/Changes
  lib/ExtUtils/CBuilder/Changes lib/ExtUtils/Changes lib/ExtUtils/NOTES
  lib/ExtUtils/PATCHING lib/ExtUtils/README lib/Module/Build/Changes
  lib/Net/Ping/Changes lib/Test/Harness/Changes
  lib/Term/ANSIColor/ChangeLog lib/Term/ANSIColor/README README.symbian

Build, Configure, Make, Install

  Configure             − help finding hints from uname,
                          shared libperl required for dynamic loading
  Makefile.SH Cross/Makefile−cross−SH
                        − linklibperl
  Porting/patchls       − cygwin in port list
  installman            − man pages with :: translated to .
  installperl           − install dll, install to 'pods'
  makedepend.SH         − uwinfix          − file permissions
  symbian/ symbian/
  win32/Makefile win32/


  t/io/fs.t             − no file mode checks if not ntsec
                                                    skip rename() check when not check_case:relaxed
  t/io/tell.t           − binmode
  t/lib/cygwin.t        − builtin cygwin function tests
  t/op/groups.t         − basegroup has ID = 0
  t/op/magic.t          − $^X/symlink WORKAROUND, s/.exe//
  t/op/stat.t           − no /dev, skip Win32 ftCreationTime quirk
                                                    (cache manager sometimes preserves ctime of file
                                                    previously created and deleted), no −u (setuid)
  t/op/taint.t          − can't use empty path under Cygwin Perl
    t/op/time.t                     − no tzset()

Compiled Perl Source

   EXTERN.h                           − __declspec(dllimport)
    XSUB.h                               − __declspec(dllexport)
    cygwin/cygwin.c             − os_extras (getcwd, spawn, and several Cygwin:: functions)
  perl.c                − os_extras, −i.bak
  perl.h                − binmode
  doio.c                − win9x can not rename a file when it is open
  pp_sys.c              − do not define h_errno, init _pwent_struct.pw_comment
  util.c                − use setenv
  util.h                − PERL_FILE_IS_ABSOLUTE macro
  pp.c                  − Comment about Posix vs IEEE math under Cygwin
  perlio.c              − CR/LF mode
  perliol.c             − Comment about EXTCONST under Cygwin

Compiled Module Source

                        − Can't install via CPAN shell under Cygwin
                        − Cygwin is Unix−like and has vsnprintf
  ext/Errno/Errno_pm.PL − Special handling for Win32 Perl under Cygwin
  ext/POSIX/POSIX.xs    − tzname defined externally
                        − EXTCONST needs to be redefined from EXTERN.h
                        − binary open
                        − Cygwin has syslog.h
                        − Convert paths to Windows paths
                        − Various timers not available
                        − Find w32api/windows.h
  ext/Win32/Makefile.PL − Use various libraries under Cygwin
  ext/Win32/Win32.xs    − Child dir and child env under Cygwin
                        − _open_osfhandle not implemented under Cygwin
                                                − __declspec(dllexport)

Perl Modules/Scripts

  ext/B/t/ − Comment about stderr/stdout order under Cygwin
                        − Use binary mode under Cygwin
                        − Convert paths to Windows paths
                        − Comment about various timers not available
                        − _open_osfhandle not implemented under Cygwin
                        − History of Win32CORE under Cygwin
  lib/            − binmode and path separator
  lib/            − hook to internal Cwd::cwd
                        − use gcc for ld, and link to libperl.dll.a
                        − Cygwin is Unix−like
  lib/ExtUtils/ − Install and rename issues under Cygwin
  lib/ExtUtils/    − OS classifications
  lib/ExtUtils/ − Example for Cygwin
                        − require
                        − canonpath, cflags, manifypods, perl_archive
  lib/File/     − Comment about quotes using a Cygwin example
    lib/File/           − on remote drives stat() always sets st_nlink to 1
  lib/File/Spec/ − case_tolerant
  lib/File/Spec/ − preserve //unc
  lib/File/Spec/ − References a message on
  lib/File/      − Pulls in lib/File/Spec/
  lib/File/      − no directory sticky bit
  lib/Module/Build/ − Comment references 'make' under Cygwin
                        − Use '.' for man page separator
  lib/Module/   − Cygwin is Unix−like
  lib/Module/ − List of all module files and versions
  lib/Net/     − No domainname command under Cygwin
    lib/Net/           − Bypass using stat() under Cygwin
  lib/Net/       − ECONREFUSED is EAGAIN under Cygwin
  lib/Pod/       − Set 'pods' dir
  lib/Pod/Perldoc/ − '−c' switch for pod2man
  lib/Pod/    − Use 'less' pager, and use .exe extension
  lib/Term/ − Cygwin terminal info
  lib/        − use stdin not /dev/tty
  utils/perlbug.PL      − Add CYGWIN environment variable to report

Perl Module Tests



Support for swapping real and effective user and group IDs is incomplete. On WinNT Cygwin provides "setuid()", "seteuid()", "setgid()" and "setegid()". However, additional Cygwin calls for manipulating WinNT access tokens and security contexts are required.


Charles Wilson <>, Eric Fifer <>, alexander smishlajev <>, Steven Morlock <>, Sebastien Barre <>, Teun Burgers <>, Gerrit P. Haase <>, Reini Urban <>, Jan Dubois <>, Jerry D. Hedden <>.


Last updated: 2012−02−08


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