You may wish to specify settings of several important environment variables that affect Cygwin's operation. Some of these settings need to be in effect prior to launching the initial Cygwin session (before starting your bash shell, for instance), and are, consequentially, best placed in a .bat file. An initial file is named Cygwin.bat and is created in the Cygwin root directory that you specified during setup. Note that the "Cygwin" option of the Start Menu points to Cygwin.bat. Edit Cygwin.bat to your liking or create your own .bat files to start Cygwin processes. The CYGWIN variable is used to configure many global settings for the Cygwin runtime system. Initially you can leave CYGWIN unset or set it to tty (e.g. to support job control with ^Z etc...) using a syntax like this in the DOS shell, before launching bash. C:\> set CYGWIN=tty notitle glob Locale support is controlled by the LANG and LC_xxx environment variables. You can set all of them but Cygwin itself only honors the variables LC_ALL, LC_CTYPE, and LANG, in this order, according to the POSIX standard. The first one found rules. For a more detailed description see . The PATH environment variable is used by Cygwin applications as a list of directories to search for executable files to run. This environment variable is converted from Windows format (e.g. C:\Windows\system32;C:\Windows) to UNIX format (e.g., /cygdrive/c/Windows/system32:/cygdrive/c/Windows) when a Cygwin process first starts. Set it so that it contains at least the x:\cygwin\bin directory where "x:\cygwin is the "root" of your cygwin installation if you wish to use cygwin tools outside of bash. This is usually done by the batch file you're starting your shell with. The HOME environment variable is used by many programs to determine the location of your home directory and we recommend that it be defined. This environment variable is also converted from Windows format when a Cygwin process first starts. It's usually set in the shell profile scripts in the /etc directory. The TERM environment variable specifies your terminal type. It is automatically set to cygwin if you have not set it to something else. The LD_LIBRARY_PATH environment variable is used by the Cygwin function dlopen () as a list of directories to search for .dll files to load. This environment variable is converted from Windows format to UNIX format when a Cygwin process first starts. Most Cygwin applications do not make use of the dlopen () call and do not need this variable. Cygwin's heap is extensible. However, it does start out at a fixed size and attempts to extend it may run into memory which has been previously allocated by Windows. In some cases, this problem can be solved by adding an entry in the either the HKEY_LOCAL_MACHINE (to change the limit for all users) or HKEY_CURRENT_USER (for just the current user) section of the registry. Add the DWORD value heap_chunk_in_mb and set it to the desired memory limit in decimal MB. It is preferred to do this in Cygwin using the regtool program included in the Cygwin package. (For more information about regtool or the other Cygwin utilities, see or use the --help option of each util.) You should always be careful when using regtool since damaging your system registry can result in an unusable system. This example sets memory limit to 1024 MB: regtool -i set /HKLM/Software/Cygwin/heap_chunk_in_mb 1024 regtool -v list /HKLM/Software/Cygwin Exit all running Cygwin processes and restart them. Memory can be allocated up to the size of the system swap space minus any the size of any running processes. The system swap should be at least as large as the physically installed RAM and can be modified under the System category of the Control Panel. Here is a small program written by DJ Delorie that tests the memory allocation limit on your system: main() { unsigned int bit=0x40000000, sum=0; char *x; while (bit > 4096) { x = malloc(bit); if (x) sum += bit; bit >>= 1; } printf("%08x bytes (%.1fMb)\n", sum, sum/1024.0/1024.0); return 0; } You can compile this program using: gcc max_memory.c -o max_memory.exe Run the program and it will output the maximum amount of allocatable memory. Internationalization support is controlled by the LANG and LC_xxx environment variables. You can set all of them but Cygwin itself only honors the variables LC_ALL, LC_CTYPE, and LANG, in this order, according to the POSIX standard. The content of these variables should follow the POSIX standard for a locale specifier. The correct form of a locale specifier is language[[_TERRITORY][.charset][@modifier]] "language" is a lowercase two character string per ISO 639-1, "TERRITORY" is an uppercase two character string per ISO 3166, charset is one of a list of supported character sets, and the modifier doesn't matter here (though it might for some applications). If you're interested in the exact description, you can find it in the online publication of the POSIX manual pages on the homepage of the Open Group. Typical locale specifiers are "de_CH" language = German, territory = Switzerland, default charset "fr_FR.UTF-8" language = french, territory = France, charset = UTF-8 "ko_KR.eucKR" language = korean, territory = South Korea, charset = eucKR And let's not forget the default locale called "C" or "POSIX" which basically only supports plain ASCII code. If the aforementioned environment variables are not set, or set to "C" or "POSIX", you get the default ASCII-only behaviour. Right now the language and territory, as well as the modifier, are not important to Cygwin, except to fix a single problem. There's a class of characters in the Unicode character set, called the "CJK Ambiguous Width Character set". For these characters the width returned by the wcwidth/wcswidth function is usually 1. This is often a problem in East-Asian languages, which historically use character sets in which these characters have a width of 2. Kind of explains why they are called "ambiguous"... The problem has been fixed for now like this. wcwidth/wcswidth usually return 1 as the width of these characters. However, if the language is specifed as "ja" (Japanese), "ko" (Korean), or "zh" (Chinese), wcwidth returns 2 for these characters. Unfortunately this isn't correct in all circumstances, so the user can specify the modifier "@cjknarrow", which modifies the behaviour of wcwidth/wcswidth to return 1 for the ambiguous width characters to return 1 even in those languages. Other than that, the only important part so far is the character set. How does that work? The default locale is the "C" or "POSIX" locale. In this locale, basically only ASCII characters are supported. Even if one of the aforementioned environment variables are set to something else, it's the application's responsibility to call the function setlocale, typically like this setlocale (LC_ALL, ""); to switch to another locale according to the settings of the internationalization environment variables. Assume that you've set one of the aforementioned environment variables to some valid POSIX locale value, other than "C" and "POSIX", and assume that you call an application which calls setlocale as above. Assume further that you're living in Japan. You might want to use the language code "ja" and the territory "JP", thus setting, say, LANG to "ja_JP". You didn't set a character set, so what will Cygwin use now? Easy! It will use the default Windows ANSI codepage of your system, if it's supported by Cygwin. Hopefully Cygwin supports all relevant default ANSI codepages... For a list of supported character sets, see You don't want to use the default Windows codepage as character set? In that case you have to specify the charset explicitly. For instance, assume you're from Italy and don't want to use the default Windows codepage 1252, but the more portable ISO-8859-15 character set. What you can do is to set the LANG variable in the C:\cygwin\Cygwin.bat file which is the batch file to start a Cygwin session from the "Cygwin" desktop shortcut. @echo off C: chdir C:\cygwin\bin set LANG=it_IT.ISO-8859-15 bash --login -i Most singlebyte or doublebyte charsets have a disadvantage. Windows filesystems use the Unicode character set in the UTF-16 encoding to store filename information. Not all characters from the Unicode character set are available in a singlebyte or doublebyte charset. While Cygwin has a workaround to access files with unusual characters (see ), a better workaround is to use always the UTF-8 character set. UTF-8 is the only multibyte character set which can represent every Unicode character. set LANG=es_MX.UTF-8 For a description of the Unicode standard, see the homepage of the Unicode Consortium. You can set the above internationalization variables not only in Cygwin.bat or in the Windows environment, but also in your Cygwin shell on the fly, even switch to yet another character set, and yet another. In bash for instance: bash$ export LC_CTYPE="nl_BE.UTF-8" However, here's a problem. At the start of the first Cygwin process in a session, the Windows environment has to be converted from UTF-16 to some singlebyte or multibyte charset. If the internationalization environment variable hasn't been set before starting this process, Cygwin has to make an educated guess which charset to use to convert the environment itself. The only reproducible way to do that in the absence of LC_ALL, LC_CTYPE, or LANG, is to use the "C" locale. The default conversion in the "C" locale used by Cygwin internally is UTF-8. So, in the absence of any internationalization environment variable, the environment will be converted to UTF-8. As long as the environment only contains ASCII characters, this is no problem at all. But if it contains native characters, and you're planning to use, say, GBK, the environment will result in invalid characters in the GBK charset. This would be especially a problem in variables like PATH. Per POSIX, the name of an environment variable should only consist of valid ASCII characters, and only of uppercase letters, digits, and the underscore for maximum portablilty. Symbolic links, too, may pose a problem when switching charsets on the fly. A symbolic link contains the filename of the target file the symlink points to. When a symlink had been created with older versions of Cygwin, the current ANSI or OEM character set had been used to store the target filename, dependent on the old CYGWIN environment variable setting codepage (see . If the target filename contains non-ASCII characters and you use another character set than your default ANSI/OEM charset, the target filename of the symlink is now potentially an invalid character sequence in the new character set. This behaviour is not different from the behaviour in other Operating Systems. So, if you suddenly can't access a symlink anymore which worked all these years before, maybe it's because you switched to another character set. This doesn't occur with symlinks created with Cygwin 1.7 or later. Except for LC_ALL, LC_CTYPE, and LANG, all other LC_xxx environment variables, LC_COLLATE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC, and LC_TIME, are ignored right now. This means, while Cygwin supports different character sets, it does not support real localization so far. There's no support for locale-specific monetary symbols, for a decimalpoint other than '.', no support for native time formats, and no support for native language sorting orders. Cygwin's internationalization support is work in progress and we would be glad for coding help in this area. Last but not least, here's the list of currently supported character sets. The left-hand expression is the name of the charset, as you would use it in the internationalization environment variables as outlined above. The right-hand side is the number of the equivalent Windows codepage as well as the Windows name of the codepage. They are only noted here for reference. Don't try to use the bare codepage number or the Windows name of the codepage as charset in locale specifiers, unless they happen to be identical with the left-hand side. Especially in case oif the "CPxxx" style charsets, always use them with the trailing "CP". This works: set LC_ALL=en_US.CP437 This does not work: set LC_ALL=en_US.437 You can find a full list of Windows codepages on the Microsoft MSDN page Code Page Identifiers. Charset Codepage CP437 437 (OEM United States) CP720 720 (DOS Arabic) CP737 737 (OEM Greek) CP775 775 (OEM Baltic) CP850 850 (OEM Latin 1, Western European) CP852 852 (OEM Latin 2, Central European) CP855 855 (OEM Cyrillic) CP857 857 (OEM Turkish) CP858 858 (OEM Latin 1 + Euro Symbol) CP862 862 (OEM Hebrew) CP866 866 (OEM Russian) CP874 874 (ANSI/OEM Thai) CP1125 1125 (OEM Ukraine) CP1250 1250 (ANSI Central European) CP1251 1251 (ANSI Cyrillic) CP1252 1252 (ANSI Latin 1, Western European) CP1253 1253 (ANSI Greek) CP1254 1254 (ANSI Turkish) CP1255 1255 (ANSI Hebrew) CP1256 1256 (ANSI Arabic) CP1257 1257 (ANSI Baltic) CP1258 1258 (ANSI/OEM Vietnamese) ISO-8859-1 28591 (ISO-8859-1) ISO-8859-2 28592 (ISO-8859-2) ISO-8859-3 28593 (ISO-8859-3) ISO-8859-4 28594 (ISO-8859-4) ISO-8859-5 28595 (ISO-8859-5) ISO-8859-6 28596 (ISO-8859-6) ISO-8859-7 28597 (ISO-8859-7) ISO-8859-8 28598 (ISO-8859-8) ISO-8859-9 28599 (ISO-8859-9) ISO-8859-10 - (not available) ISO-8859-11 - (not available) ISO-8859-13 28563 (ISO-8859-13) ISO-8859-14 - (not available) ISO-8859-15 28565 (ISO-8859-15) ISO-8859-16 - (not available) SJIS 932 (ANSI/OEM Japanese) GBK 936 (ANSI/OEM Simplified Chinese) Big5 950 (ANSI/OEM Traditional Chinese) eucJP 20932 (EUC Japanese) eucKR 949 (EUC Korean) UTF-8 65001 (UTF-8) To set up bash so that cut and paste work properly, click on the "Properties" button of the window, then on the "Misc" tab. Make sure that "QuickEdit mode" and "Insert mode" are checked. These settings will be remembered next time you run bash from that shortcut. Similarly you can set the working directory inside the "Program" tab. The entry "%HOME%" is valid, but requires that you set HOME in the Windows environment. Your home directory should contain three initialization files that control the behavior of bash. They are .profile, .bashrc and .inputrc. The Cygwin base installation creates stub files when you start bash for the first time. .profile (other names are also valid, see the bash man page) contains bash commands. It is executed when bash is started as login shell, e.g. from the command bash --login. This is a useful place to define and export environment variables and bash functions that will be used by bash and the programs invoked by bash. It is a good place to redefine PATH if needed. We recommend adding a ":." to the end of PATH to also search the current working directory (contrary to DOS, the local directory is not searched by default). Also to avoid delays you should either unset MAILCHECK or define MAILPATH to point to your existing mail inbox. .bashrc is similar to .profile but is executed each time an interactive bash shell is launched. It serves to define elements that are not inherited through the environment, such as aliases. If you do not use login shells, you may want to put the contents of .profile as discussed above in this file instead. shopt -s nocaseglob will allow bash to glob filenames in a case-insensitive manner. Note that .bashrc is not called automatically for login shells. You can source it from .profile. .inputrc controls how programs using the readline library (including bash) behave. It is loaded automatically. For full details see the Function and Variable Index section of the GNU readline manual. Consider the following settings: # Ignore case while completing set completion-ignore-case on # Make Bash 8bit clean set meta-flag on set convert-meta off set output-meta on The first command makes filename completion case insensitive, which can be convenient in a Windows environment. The next three commands allow bash to display 8-bit characters, useful for languages with accented characters. Note that tools that do not use readline for display, such as less and ls, require additional settings, which could be put in your .bashrc: alias less='/bin/less -r' alias ls='/bin/ls -F --color=tty --show-control-chars'