In the famous Aardman Animations short film “Creature Comforts“, a variety of zoo animals discuss their lives in the zoo.  A Brazilian Lion speaks at length about the virtue of the great outdoors (cf. a zoo) recalling that in Brazil “We have space“.  While space might be a great thing for Brazilian Lions, it turns out that space is a dangerous and difficult reality in path names for computer applications.

In a recent contract, one portion of the work involved running an existing Windows application under Cygwin. Cygwin, for the uninitiated, is an emulation of the bash shell and most standard Unix commands. It provides this functionality so you can experience Unix under Windows. The Windows application I was working on had been abandoned for several years and customer pressure finally reached a level at which maintenance and updates were required – nay, demanded. Cygwin support was required primarily for internal infrastructure reasons. The infrastructure was a testing framework – primarily comprising bash shell scripts – that ran successfully on Linux (for other applications). My job was to get the Windows application re-animated and running under the shell scripts on Cygwin.

It turns out that the Windows application had a variety of issues with spaces in path names. Actually, it had one big issue – it just didn’t work when the path names had spaces. The shell scripts had a variety of issues with spaces. Well, one big issue – they, too, just didn’t work when the path names had spaces. And it turns out that some applications and operations in Cygwin have issues with spaces, too. Well, that one big issue – they don’t like spaces.

Now by “like”, I mean that when the path name contains spaces then even using ‘\040’ (instead of the space) or quoting the name (e.g., “Documents and Settings”) does not resolve matters and instead merely yields unusual and unhelpful error messages. The behavior was completely unpredictable, as well. For instance, quoting might get you part way through a section of code but then the same quoted name failed when used to call stat. It would then turn out that stat didn’t like spaces in any form (quoted, escaped, whatever…).

Parenthetically, I would note that the space problem is widespread. I was doing some Android work and having an odd an unhelpful error displayed (“invalid command-line parameter”) when trying to run my application on the emulator under Eclipse. It turns out that a space in the path name to the Android SDK was the cause.  Once the space was removed, all was well.

The solution to my problem turned out to be manifold. It involved a mixture of quoting, clever use of cygpath and the Windows API calls GetLongPathName and GetShortPathName.

When assigning and passing variables around in shell scripts, quoting a space-laden path or a variable containing a space-laden path,  the solution was easy. Just remember to use quotes:

THIS=”${THAT}”

Passing command line options that include path names with spaces tended to be more problematic. The argc/argv parsers don’t like spaces.  They don’t like them quoted and don’t like them escaped.  Or maybe the parser likes them but the application doesn’t. In any event, the specific workaround that used was clever manipulation of the path using the cygpath command. The cygpath -w -s command will translate a path name to the Windows version (with the drive letter and a colon at the beginning) and then shortens the name to the old-style 8+3 limited format thereby removing the spaces. An additional trick is that then, if you need the cygwin style path – without spaces – you get the output of the cygpath -w -s and run it through cygpath -u. Then you get a /cygdrive/ style file name with no spaces. There is no other direct path to generating a cygwin Unix style file name without spaces.

These manipulations allow you to get the sort of input you need to the various Windows programs you are using. It is important to note, however, that a Windows GUI application built using standard file browser widgets and the like always passes fully instantiated, space-laden path names. The browser widgets can’t even correctly parse 8+3 names. Some of the system routines, however, don’t like spaces. Then the trick is how do you manipulate the names once within the sphere of the Windows application? Well, there are a number of things to keep in mind, the solutions I propose will not work with cygwin Unix-style names and they will not work with relative path names.

Basically, I used the 2 windows API calls GetLongPathName and GetShortPathName to manipulate the path. I used GetShortPathName to generate the old-style 8+3 format name that removes all the spaces. This ensured that all system calls worked without a hitch. Then, in order, to display messaging that the end-user would recognize, make sure that the long paths are restored by calling GetLongPathName for all externally shared information. I need to emphasize that these Windows API calls do not appear to work with relative path names. They return an empty string as a result. So you need to watch out for that.

Any combination of all these approaches (in whole or in part) may be helpful to you in resolving any space issues you encounter.