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Date:      Sun, 19 May 2013 00:06:47 +0000
From:      "Teske, Devin" <Devin.Teske@fisglobal.com>
To:        Quartz <quartz@sneakertech.com>
Cc:        "<freebsd-questions@freebsd.org>" <freebsd-questions@freebsd.org>
Subject:   Re: check variable content size in sh script
Message-ID:  <13CA24D6AB415D428143D44749F57D7201F508F2@ltcfiswmsgmb26>
In-Reply-To: <519814A7.8070702@sneakertech.com>
References:  <5194F65F.6080503@a1poweruser.com> <5194FB0A.9090400@tundraware.com> <13CA24D6AB415D428143D44749F57D7201F4D41F@ltcfiswmsgmb26> <5197998E.6050200@sneakertech.com> <51979A8B.8080703@tundraware.com> <5197A526.7020302@sneakertech.com> <20130518180634.9e5fd3c2.freebsd@edvax.de> <519814A7.8070702@sneakertech.com>

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On May 18, 2013, at 4:54 PM, Quartz wrote:

>=20
>> #foo works with sh
>=20
> Is it actually part of the official spec though is what I'm wondering, or=
 is it a case of other shells not rejecting 'advanced' statements when runn=
ing in emulation.
>=20

Shells don't have an "emulation mode". The shell supports what it supports,=
 and no shell that I've ever used had an "emulation mode" to act like anoth=
er shell.

Maybe you're referring to as "emulation" is actually the invocation line of=
 the shell script.

Make no mistake=85 when you change the invocation (first) line of a shell s=
cript from:

	#/bin/sh

to:

	#/bin/tcsh

You are not instructing a shell to "emulate" anything, you are actually usi=
ng a different shell.

sh !=3D tcsh !=3D bash !=3D ash !=3D dash !=3D zsh

Your script will use the shell that is written in the innovation line and t=
he features you get are respective to which shell you choose.



>=20
>> At least FreeBSD's implementation of sh (which is ash, I think)
>> supports the # functionality.
>=20
> The reason I say all this is that my copy of tcsh (on this not-freebsd ma=
chine) *doesn't* work with this when in sh emulation.
>=20

Get the idea that "csh" or "tcsh" are *anything* like sh out of your mind.

Further, you almost *never* want to do any serious shell programming in csh=
 or tcsh.

Why? Because csh and tcsh have an incomplete programming spec. Most notably=
 are the way that it handles pipe data and the standard-output/error file d=
escriptors. Specifically, you cannot throw away stdout while keeping stderr=
. This short-coming may not be noticeable to all programmers that choose cs=
h/tcsh, but if you want to do any serious programming, you'll eventually hi=
t those limitations and be forced to move to a real shell (real in the sens=
e that it has a complete programming specification).

I personally never recommend csh/tcsh as a scripting language=85 but I can =
see the benefit that certain constructs (like "repeat N cmd") have, purely =
for their simplicity (and readability for *very* short scripts). To challen=
ge myself on this topic, I routinely try and cross-port very complex shell =
scripts to csh, and while I can do math with "let" and I can other things t=
hat a *normal* scripting language should allow=85 I invariably end up runni=
ng away screaming in frustration.

Again,

csh !=3D tcsh !=3D sh !=3D bash !=3D ash !=3D dash !=3D zsh
--=20
Devin

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