I want to write and test scripts that do not depend on any of the personal environment variables accessible to me at the command line. For instance, each time I open a new command line window on my macbook pro, $PATH is updated by having my personal bin directory prepended to it --- as well as several other directories, such as
/usr/sbin:/sbin:/Library/TeX/texbin:/Library/Apple/usr/bin
This occurs apparently because my $HOME/.profile is automatically sourced when a window opens up. In addition, a large number of other variables are defined at login because my personal .bashrc is sourced automatically.
Ultimately, I want to be able to run a script as a cron job --- using crontab -l. But if the script depends on my personal configuration, or if it tries to access a script that lives in my personal bin, it will halt with error.
So I write a script, test it at the command line, set up a cron job to run it; and when the time comes, it halts with error, because it turns out that the script depended on one of my personal environment variables.
Currently, then, the only way I know to test such a script is to set up a cron job --- say, five minutes from now---and then wait for the cron job to run. It's clumsy and slow.
Is there a direct and immediate way to run a script so that it does not know anything from $HOME/.profile?
The script I tested this with:
#!/usr/bin/perl
use strict; use warnings;
use Data::Dumper qw(Dumper);
$Data::Dumper::Sortkeys = 1;
print Dumper {%ENV};
The following command
> jaw20210419test.pl | wc
2532 3098 118462
produces many lines of output, as you see, because of all that I define in my .bashrc. With the following,
> sudo jaw20210419test.pl | wc
Password:
20 59 831
>
the output is much less, but it still has an updated $PATH including my personal bin. I do not understand this, since the $PATH gets updated by $HOME/.profile, and that file sources my personal $HOME/u/kh/.bashrc.
If however I run this with a cron job, then it does not have an updated $PATH. The script says
$VAR1 = {
'HOME' => '/Users/kpr',
'LOGNAME' => 'kpr',
'PATH' => '/usr/bin:/bin',
'PWD' => '/Users/kpr',
'SHELL' => '/bin/sh',
'SHLVL' => '1',
'USER' => 'kpr',
'VERSIONER_PERL_VERSION' => '5.18',
'_' => '/Users/kpr/u/kh/bin/jaw20210419test.pl',
'__CF_USER_TEXT_ENCODING' => '0x1F5:0x0:0x0'
};
This is the configuration I want to test the script with. Note that it knows who I am --- $USER --- and where $HOME is.
By contrast, two other proposed solutions, from
How to start a shell without any user configuration?,
do not even know know where $HOME is:
> echo $cdbin # personal environment variable
/Users/kpr/u/kh/bin
> env -i perl $cdbin/jaw20210419test.pl
$VAR1 = {
'VERSIONER_PERL_VERSION' => '5.18',
'__CF_USER_TEXT_ENCODING' => '0x1F5:0x0:0x0'
};
> env --noprofile --norc perl $cdbin/jaw20210419test.pl
env: illegal option -- n
usage: env [-iv] [-P utilpath] [-S string] [-u name]
[name=value ...] [utility [argument ...]]
> echo $SHELL
/bin/bash
>
> env -i sh -c $cdbin/jaw20210419test.pl
$VAR1 = {
'PWD' => '/Users/kpr/u/sng/2021/FR-Wegelin-TO-stackoverflow',
'SHLVL' => '1',
'VERSIONER_PERL_VERSION' => '5.18',
'_' => '/Users/kpr/u/kh/bin/jaw20210419test.pl',
'__CF_USER_TEXT_ENCODING' => '0x1F5:0x0:0x0'
};
so I am still lost.
Of note, you can not technically do what you wish. Bash goes to great lengths to determine if you are running an interactive shell or a non-interactive shell. Running from cron will forever be non-interactive as is running from a terminal will forever be marked as interactive.
You want a number of entries not present in cron for your test shell, for example PS1 for a prompt. Also there are quite a few read only environment variables. If you try to unset them you get an error:
You can get 95 percent there by this method:
The file
be-cron.shwill "unset" most of the interactive environment variables: