Dezember 2008

I stumpled upon something funny at work today. It might help being a fellow programmer to consider this being funny. It took some time today to come up with a solution ...

Task: Change a path in a text file during a build process using the java build tool ant.

Solution: Use a Regular Expression to scan the text file and replace the value.

This is where the madness begins: You need to escape a backslash. Probably multiple times ...

2⁰ = 1
The path contains one backslash:
C:\my\path

2¹ = 2
You need to escape the \ in the properties file, it should read:
my.path=C:\\my\\path

2² = 4
If you want to print the Path in a Java String (which ant more or less uses), you need to escape each \ with \\, that becomes:

"C:\\\\my\\\\path"

2³ = 8
If you want to put that in a regular expression, you need to escape each \ with \\, which will lead to:
"C:\\\\\\\\my\\\\\\\\path"

2⁴ = 16
This expression should be generated by another regular expression, so each \ needs to be replaced with \\, hence:
"C:\\\\\\\\\\\\\\\\my\\\\\\\\\\\\\\\\path"

2⁵ = 32
Put the thing into an build.xml file for ant, you you'll end up with 32 (thirty two!!!) backslashes to have one in the end. Without escaping 1 (one) backslash with 16 backslashes (written as 32, because each one of those 16 needs to be escaped), it won't work:

<propertyregex br="" 
    property="jboss.dir.escaped">             
    input="${$jboss.dir}" regexp="\\"
    replace="\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"
    global="true"/>
<replaceregexp br="" 
    match="(?<=jboss.local.dir=).*$"
    replace="${jboss.dir.escaped}" 
    flags="gm">
        <!-- yadda, yadda, yadda -->
</replaceregexp>

Now that's efficiency. Thanks a lot, java folks.

Things like that never happen to me in perl. Oh dear perl, I really love you. For a reason.