[arm-allstar] File extensions and audio format

[Willem Schreuder]

On Thu, 11 Feb 2016, Chris Zenchenko wrote:

> Why in some cases do they have extensions and in others they don't?
> Should they all have extensions?

I'll weigh in on this part of question:

File extensions on Unix/Linux systems typically do not matter.  In a few 
instances like C programs, the .c is used by the compiler to distinguish 
foo.c from foo.o (source code versus object code), but that is a naming 
convention and is not actually inherent in defining the file.

Executable programs on Linux/Unix systems are defined by their "magic". 
For scripts, it is typically the first line in the file, e.g.

#!/usr/bin/perl

or

#!/usr/bin/python

The shell will look at that line and if it is present, it will invoke the 
perl or python interpreter to run the file.  Since the # makes it a 
comment for the interpreter it is ignored.  In Unix speak this is called a 
"shebang line" (hash + bang, and ok yes we have a strange sense of humor)

Using a .py and .pl file extension makes it obvious that it is actually a 
python or Perl script, but that is for the user only.  Unlike Windows, the 
OS attaches no special meaning to the .py and .pl extension.

The same thing is true for shell scripts.  You can add
#!/bin/bash
to the beginning of the file and invoke the bash shell explicitly, or if 
you omit that the script gets processed by whatever shell you use.  On 
Linux systems the bash shell is pretty much universally used.

The .sh extension is a clue to the user, but has no special meaning to the 
OS.

I personally tend to omit .pl, .py, .sh and so on.  The language in which 
a command or shell script is written only matters if you want to change 
it.  The only time I would use an extension is if I need to distinguish 
say a system command foo and a shell script foo.sh which invokes that 
command with a special set of parameters, or something of that nature.  In 
those cases, however, I tend to use the case sensitivity.  So foo is the 
command and Foo is a shell script that runs foo in some special way.  But 
that's just me.

If you want to see what a command is (i.e. script, executable, etc) you 
can use the 'file" command.  Doing
   file foo
tells you more about what kind of file it is.  It uses the signatures in 
the /etc/magic file to figure out the file type based on its contents 
rather than the name of the file.  It makes an interesting read.

73 Willem AC0KQ

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Dr. Willem A. Schreuder,  President,  Principia Mathematica
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