difference between file extensions?

What is the difference between these extensions:

1. *.htm or *.开发者_开发百科html //HTML
2. *.jpg or *.jpeg or *.jpe //Picture format
3. *.pl or *.plx //Perl

Thanks,

htm vs html

jpg jpeg etc

pl vs plx

Nothing, really, except how your operating system may choose to associate them with applications. HTTP itself doesn't even care about extensions.

Some of them are historical. .htm stems from the DOS/Windows 3.1 days, when filenames had to be in the "8.3" format, that is, eight characters for the filename, a dot, and three (and only three) letters for the file extension.

See this:

List of File Formats

Certain operating systems such as DOS and early versions of Windows had a 3 character limit for the file extension. More modern incarnations of Windows still generate these kind of short file names (a.k.a 8.3 filename) for files with longer file names in order to maintain compatibility with some legacy software.

There is no difference between files with the extension .htm vs .html or those with .jpg vs .jpeg.

As for .pl vs .plx, refer to this link from VoodooChild's post.

Edit: Note that technically a .pl file could be a Prolog source file in which case.pl could be considered different from the .plx extension of a Perl script.