Variable assignment in sh

Valeri Galtsev galtsev at kicp.uchicago.edu
Tue Jan 31 18:21:57 UTC 2017


On Tue, January 31, 2017 11:51 am, Polytropon wrote:
> On Tue, 31 Jan 2017 12:11:49 -0500, James B. Byrne via freebsd-questions
> wrote:
>>
>> On Tue, January 31, 2017 10:18, Polytropon wrote:
>> > On Tue, 31 Jan 2017 10:06:37 -0500, James B. Byrne via
>> > freebsd-questions wrote:
>> >> Why am I getting this result when I attempt a simple variable
>> >> assignment in the default sh?
>> >>
>> >> # ENV=$HOME/.shrc; export ENV
>> >> ENV=/root/.shrc: Command not found.
>> >> export: Command not found.
>> >>
>> >> This example is taken verbatim from the sh manpage provided with
>> >> FreeBSD.
>> >
>> > This looks like you're running a sh command inside csh.
>> > Note that the C shell (FreeBSD's default interactive shell)
>> > does variable assignments differently:
>> >
>> > 	setenv ENV /root/.shrc
>> >
>> > 	set FOO = 1
>> >
>> > See "man csh" for details.
>> >
>> > The command you've presented looks like it would belong into
>> > a shell script (FreeBSD's default scripting shell)...
>> >
>>
>> I note that root is configured in FreeBSD with a default shell of
>> /bin/csh and that the user toor has no default shell specified at all
>> notwithstanding having a Real Name of 'Bourne-again Superuser'.  I
>> checked several of our FreeBSD hosts and all have the same
>> configuration for root and toor so I infer that this is how FreeBSD is
>> shipped.
>
> That is correct. The user toor has no shell assigned per
> default ("inactive user"), and root, as well as all other
> users, default to the C shell as the login shell (which
> typically is an interactive shell).

Regular users do not default to csh, but to sh if you don't specify
particular shell on "pw adduser" command.
That aside, thanks a lot for your instructive explanations!!

Valeri

> The real names for
> the users can be set according to your needs, they have
> a more or less "descriptive value". :-)
>
>
>
>> My problem was running a status check command from cron.  Having noted
>> that it was failing I tried testing the command having logged on to
>> the FreeBSD server as root (using ssh with certificates). This is the
>> user with which cron is configured to execute this particular command.
>
> You simply ran into the "wrong shell" problem. :-)
>
>
>
>> I am somewhat puzzled by your comment:
>>
>> > a shell script (FreeBSD's default scripting shell)
>>
>> What does this mean exactly?  Is not CSH a shell?  I thought that the
>> shell used in cron was the shell of the user associated with the
>> crontab file?  What is cron's default shell otherwise?
>
> FreeBSD comes with two shells:
>
> sh (Bourne shell, actually an Almquist shell) is the shell that
> is used for scripting. Most shell scripts start with #!/bin/sh,
> which refers to that shell.
>
> csh (C shell, actually a tcsh) is the shell for interactive logins
> and dialog use. Many users prefer to replace it with something
> they add from ports or packages, like zsh or bash. It is possible
> to use that shell for scripting as well, but nobody actually does
> this because it's quite terrible. :-)
>
> As cron usually executes shell scripts, sh is being used (and
> that explains the sh syntax you've mentioned). The system-wide
> /etc/crontab defines SHELL and PATH for commands it executes.
>
> If you'd wanted to interactively test something you want to run
> via cron, execute "sh" from your csh prompt to run an interactive
> session. Keep in mind that sh _can_ be used interactively too,
> but it's somewhat limited in features. You can also store the
> commands in a file and execute them with "sh testfile.sh", or
> make the script executable and then run it, "chmod +x testfile.sh"
> and then "./testfile.sh".
>
>
>
>> In any case, I now have set the shell in the root crontab file
>> explicitly to /usr/local/bin/bash in hopes of avoiding this problem in
>> the future.
>
> That _might_ introduce problems in the future when bash is not
> available. My suggestion: Use /bin/sh for scripting except you
> need to rely on a "bash-ism", a feature that bash can provide,
> but sh cannot. However, you can use bash interactively to test
> sh commands, there is "backward compatibility" (bash can be seen
> as a superset of sh).
>
>
>
>
> --
> Polytropon
> Magdeburg, Germany
> Happy FreeBSD user since 4.0
> Andra moi ennepe, Mousa, ...
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++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++


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