# Exchanging the extension in a filename **URL:** \ **Category:** Ruby\ **Created:** [August 14, 2007, 12:06pm UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024 "2007-08-14T12:06:22Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 14, 2007, 12:06pm UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/1 "2007-08-14T12:06:22Z")
I have a string representing the name of a java file. I would like to get a new string, where the extension .java has been replaced by .class. My approach was to use String#sub: filename=“abc/x.java” filename.sub(/java$/,‘class’) This works fine, but I wonder whether there isn’t a more elegant way to do it. Ronald ---
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 14, 2007, 12:28pm UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/2 "2007-08-14T12:28:25Z")
On 8/14/07, Ronald F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > This works fine, but I wonder whether there isn’t a more > elegant way to do it. sub is pretty elegant. If you wanted you could do it like File.join(File.dirname(filename), File.basename(filename, “.java”) + “.class”) Ronald ---
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 14, 2007, 5:07pm UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/3 "2007-08-14T17:07:28Z")
- Ronald F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) (12:05) schrieb: > filename.sub(/java$/,‘class’) I’d match the point too, not everything that ends with “java” is java source file: filename.sub(/.java$/, ‘.class’) > This works fine, but I wonder whether there isn’t a more > elegant way to do it. What is unelegant about that? mfg, simon … l ---
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 14, 2007, 7:56pm UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/4 "2007-08-14T19:56:47Z")
On Aug 14, 5:05 am, “Ronald F.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > elegant way to do it. > > ## Ronald > > Ronald F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > Phone: +49-89-452133-162 filename = “abc/x.java” ==\>“abc/x.java” filename[/java$/] = “class” ==\>“class” filename ==\>“abc/x.class” ---
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 16, 2007, 9:55am UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/5 "2007-08-16T09:55:24Z")
> filename = “abc/x.java” > ==\>“abc/x.java” > filename[/java$/] = “class” > ==\>“class” > filename > ==\>“abc/x.class” Thanks - this is a nice alternative (for the case I actually want to modify filename). Of course it assumes that I know that the file ends in .java (but this is true in my case anyway). Ronald ---
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 16, 2007, 9:59am UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/6 "2007-08-16T09:59:24Z")
> - Ronald F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) (12:05) schrieb: > > > filename.sub(/java$/,‘class’) > > I’d match the point too, not everything that ends with “java” is java > source file: filename.sub(/.java$/, ‘.class’) In general, yes, but in my case I _know_ that the file ends in .java anyway, so matching the dot is not so important. > > This works fine, but I wonder whether there isn’t a more > > elegant way to do it. > > What is unelegant about that? Maybe I did too much shell programming before 😉 On shell level, I would do a $(dirname $FILENAME)/($basename $FILENAME java)class so I was thinking whether I might have overlooked some useful method in the FilePath or File class which would be helpful here. Thanks for the advice… Ronald ---
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 16, 2007, 10:45am UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/7 "2007-08-16T10:45:33Z")
On Aug 16, 12:57 am, “Ronald F.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > This works fine, but I wonder whether there isn’t a more > > > so I was thinking whether I might have overlooked some useful method > > > in the FilePath or File class which would be helpful here. > > Thanks for the advice… > > Ronald If what you are looking for is a way to change the extension of some ".java’ files to have the extension “.class”, you might try Rio (http:// [rio.rubyforge.org](http://rio.rubyforge.org)) require ‘rio’ rio(‘abc’).rename files(‘\*.java’) do |file| file.extname = ‘.class’ end If you want to include files in subdirectories of ‘abc’ use: rio(‘abc’).rename.all.files(‘\*.java’) do |file| file.extname = ‘.class’ end Hope this helps, > **[require 'rio'](http://rio4ruby.blogspot.com/)** > > Discussion of the Rio library for Ruby ---
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 16, 2007, 7:10pm UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/8 "2007-08-16T19:10:13Z")
Ronald F. wrote: > I have a string representing the name of a java file. I would > like to get a new string, where the extension .java has been > replaced by .class. […] > This works fine, but I wonder whether there isn’t a more > elegant way to do it. If you are _really_ lazy: require ‘rake’ # NOTE: Not running rake, just using its library. java\_file = “filename.java” class\_file = java\_file.ext(“class”) If you have a bunch of files that need this, you can do: require ‘rake’ java\_files = FileList[‘src/\*\*/\*.java’] class\_files = java\_files.ext(“class”) If you need more extensive filename manipulation, check out the “pathmap” method (available on both FileLists and Strings when using rake). – – Jim W. ---
**Author:** ![ronaldfischer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/67e7ee/32.png) [@ronaldfischer](https://www.ruby-forum.com/u/ronaldfischer)\ **Post date:** [August 16, 2007, 4:22pm UTC](https://www.ruby-forum.com/t/exchanging-the-extension-in-a-filename/112024/9 "2007-08-16T16:22:14Z")
2007/8/14, William J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > > > > filename[/java$/] = “class” > ==\>“class” > filename > ==\>“abc/x.class” I’d rather include the dot to avoid renaming files called “foo.notjava” irb(main):001:0\> f=“foo/bar.java” =\> “foo/bar.java” irb(main):002:0\> f[/.java$/]=“.class” =\> “.class” irb(main):003:0\> f =\> “foo/bar.class” Kind regards robert