Sending Tcsh to packages/ports ...

[Paul Mather]

> Date: Fri, 29 Mar 2019 03:56:38 +0100
> From: Polytropon <freebsd at edvax.de>
> To: Michael Sierchio <kudzu at tenebras.com>
> Cc: mayuresh at kathe.in, FreeBSD Questions
> 	<freebsd-questions at freebsd.org>
> Subject: Re: Sending Tcsh to packages/ports ...
> Message-ID: <20190329035638.db780898.freebsd at edvax.de>
> Content-Type: text/plain; charset=US-ASCII
> 
> On Thu, 28 Mar 2019 19:03:24 -0700, Michael Sierchio wrote:
>> *kudzu at hearst:/bin 130>* ll -i | grep csh
>> 
>> 198147 -r-xr-xr-x   2 root  wheel  427888 Jun 22  2018 csh*
>> 
>> 198147 -r-xr-xr-x   2 root  wheel  427888 Jun 22  2018 tcsh*
>> 
> 
> The csh / tcsh is not the only system component known by
> more than one name:
> 
> 	% hardlinks.sh /bin
> 	     23621: csh tcsh 	<--- !
> 	     23627: ed red 
> 	     23633: link ln 
> 	     23638: pgrep pkill 
> 	     23644: rm unlink 
> 	     24944: [ test
> 
> It's important to note that by querying $0 or argv[0], a
> program can change its behaviour depending on the way it
> has been invoked. So a call to "csh" could cause the program
> to do things differently than if it was called by "tcsh".
> 
> Of course this also applies to _any_ programs, being part
> of the OS or being installed by ports.


Indeed, this is the mechanism by which the /rescue system works: lots of hard links to a statically-linked /rescue/rescue binary, which behaves differently depending upon with which program name it's being invoked.  In the case of /rescue this saves a lot of space over having separate static binaries.

Cheers,

Paul.