# When run from cron, regex NEVER match, always give nil

**URL:** <https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984>\
**Category:** Ruby\
**Created:** [August 19, 2009, 2:52am UTC](https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984 "2009-08-19T02:52:01Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![jimdeuc](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/b77776/32.png) [@jimdeuc](https://www.ruby-forum.com/u/jimdeuc)\
**Post date:** [August 19, 2009, 2:52am UTC](https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984/1 "2009-08-19T02:52:01Z")

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I’m using ruby 1.8.6 on RHEL 5.3. I also had this problem with ruby  
1.8.5 that comes with RHEL. I had hoped the ruby upgrade would fix it  
but it didn’t.

Anyway, no regexps will match, even the most blatant matches, when the  
script is run from cron.

A line like ‘/.\*/.match(“myrandomstring”)’ matches just fine when the  
script is run from the console, but it returns nil when run from cron.  
And that regex should match ANYTHING.

I’m not sure if this is an issue with ruby or if it is something with  
cron, but I really need regex’s to work from cron scripts. Help?

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**Author:** ![jimdeuc](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/b77776/32.png) [@jimdeuc](https://www.ruby-forum.com/u/jimdeuc)\
**Post date:** [August 19, 2009, 3:10am UTC](https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984/2 "2009-08-19T03:10:20Z")

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James D. wrote:

> I’m not sure if this is an issue with ruby or if it is something with  
> cron, but I really need regex’s to work from cron scripts. Help?

It’s cron. Or rather, it’s not cron, or Ruby, but something about the  
environment that cron sets up to run your script.

Think about it. A Ruby program doesn’t “know” that it’s being run from  
cron. It just runs. There’s nothing in Ruby that says “Oh, I’ve been  
invoked from cron, so I need to do things differently.” Ruby scripts  
always do the same thing no matter how they’re invoked. Regexps match,  
or don’t match, no matter how you invoke the Ruby script.

Therefore something about the environment that is present when cron runs  
your script is different than you expect. You don’t say how you know  
that the regexp doesn’t match. What symptom of failure do you have?

99% of all cron problems are caused by PATH differences. Remember cron  
uses a different PATH than you have in your personal shell. You may have  
to specify the full path to Ruby, or something like that. See  
[Newbie: Intro to cron](http://unixgeeks.org/security/newbie/unix/cron-1.html) for some more  
info.

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**Author:** ![jimdeuc](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/b77776/32.png) [@jimdeuc](https://www.ruby-forum.com/u/jimdeuc)\
**Post date:** [August 19, 2009, 8:24pm UTC](https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984/3 "2009-08-19T20:24:43Z")

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Tim H. wrote:

> James D. wrote:
> 
> > I’m using ruby 1.8.6 on RHEL 5.3. I also had this problem with ruby  
> > 1.8.5 that comes with RHEL. I had hoped the ruby upgrade would fix it  
> > but it didn’t.

It probably has something to do with the cron not using Bash as the  
default  
shell, though why this would affect Ruby, I fail to understand. I ran  
into this  
before though. On Debian flavor machines especially a more  
Bourneshell-shell  
like minimalist shell is used as the default instead of Bash, and you  
end up  
getting it as your shell in at, and I think Cron. Is it possible your  
regex  
stuff is somehow getting stuff from a point in the shell that could lose  
the  
data if it were not Bash?

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**Author:** ![jimdeuc](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/b77776/32.png) [@jimdeuc](https://www.ruby-forum.com/u/jimdeuc)\
**Post date:** [August 20, 2009, 2:54am UTC](https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984/4 "2009-08-20T02:54:45Z")

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g\_f wrote:

> Like Tim said, it’s probably something in the environment. Besides  
> PATH, you could have other environment variables set in your BASH  
> startup that are not set when the default /bin/sh gets started.
> 
> For apps I have to run from cron, if I need to, I’ll write a  
> wrapping .sh script that sets up the environment exactly as I need it.  
> That could include switching to bash/csh/zsh or whatever, or  
> sourcing .login or .profile or manually setting variables. Cron is  
> stupid and does exactly what is said plus whatever (hidden) defaults  
> the system has set up, so figuring it out can be a real task.
> 
> I wonder if you might have installed some libraries in your own space  
> instead of the system’s Ruby space. User permission problems will crop  
> up then and can be a pain to figure out. I’d debug that by logging in  
> as whatever user the cron job runs as, then manually run the script.
> 
> You don’t say whether your job is running out of your own user’s cron,  
> or out of root’s cron, or via the system’s /etc/crontab. For my  
> production code I set up the scripts to be run as root, but that’s  
> because I’ve been doing this so long I’ve shot off most of my toes and  
> learned the hard lessons about what not to do… I’m sufficiently  
> paranoid so I’m considered a trusted user. 🙂

sorry for the silence, I’ve been swamped today (consultants are here  
doing a networking hardware upgrade). However, I was incorrent in that  
‘/.\*/.match(“myrandomstring”)’ does actually return a match when run  
from cron, but my actual regex is a bit more complicated. My actual  
regex does match when run manually though.

I think I’m going to do a little more testing and cut some parts out of  
the regex to find if maybe there is just a single unit of the expression  
that is the problem. It’s a tedious pain in the rump, though since it  
matches when run manually, I have to make a change, check the time, set  
it to run in a minute from cron, wait for it to run, check the output  
file… very tedious and time-consuming.

This is run by root’s cron by the way. I don’t how to do “sourcing  
.login or .profile” but I did try making a wrapper script with a  
/bin/bash hashbang that then just calls the ruby script, and that didn’t  
make any difference.

---

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**Author:** ![jimdeuc](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/b77776/32.png) [@jimdeuc](https://www.ruby-forum.com/u/jimdeuc)\
**Post date:** [August 20, 2009, 12:37am UTC](https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984/5 "2009-08-20T00:37:37Z")

</div>

Like Tim said, it’s probably something in the environment. Besides  
PATH, you could have other environment variables set in your BASH  
startup that are not set when the default /bin/sh gets started.

For apps I have to run from cron, if I need to, I’ll write a  
wrapping .sh script that sets up the environment exactly as I need it.  
That could include switching to bash/csh/zsh or whatever, or  
sourcing .login or .profile or manually setting variables. Cron is  
stupid and does exactly what is said plus whatever (hidden) defaults  
the system has set up, so figuring it out can be a real task.

I wonder if you might have installed some libraries in your own space  
instead of the system’s Ruby space. User permission problems will crop  
up then and can be a pain to figure out. I’d debug that by logging in  
as whatever user the cron job runs as, then manually run the script.

You don’t say whether your job is running out of your own user’s cron,  
or out of root’s cron, or via the system’s /etc/crontab. For my  
production code I set up the scripts to be run as root, but that’s  
because I’ve been doing this so long I’ve shot off most of my toes and  
learned the hard lessons about what not to do… I’m sufficiently  
paranoid so I’m considered a trusted user. 🙂

---

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**Author:** ![jimdeuc](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/b77776/32.png) [@jimdeuc](https://www.ruby-forum.com/u/jimdeuc)\
**Post date:** [August 20, 2009, 4:21am UTC](https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984/6 "2009-08-20T04:21:48Z")

</div>

On Aug 19, 2009, at 17:54 , James D. wrote:

> expression  
> make any difference.  
> I can almost guarantee it has nothing to do with cron itself.

You can start to isolate your problems in a couple of ways. One thing  
I use is:

alias newshell=‘env -i $SHELL --norc’

that brings up a new shell in your terminal that is about as virginal  
and bare as what cron runs with.

Another is to set up a side cron task like:

- 
  - 
    - 
      - 
        - /usr/bin/ruby -e ‘p /.\*/.match(“myrandomstring”)’

and wait for the mail landslide to start (or tack on 2\>&1 \>\> /tmp/  
cron.wtf)

From there, build it up until you can replicate your problem  
properly. Pathing, system calls, tainting/SAFE modes… whatever it is  
that is actually tripping you up. Find it.

Good luck.

---

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**Author:** ![jimdeuc](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/b77776/32.png) [@jimdeuc](https://www.ruby-forum.com/u/jimdeuc)\
**Post date:** [August 20, 2009, 4:19am UTC](https://www.ruby-forum.com/t/when-run-from-cron-regex-never-match-always-give-nil/173984/7 "2009-08-20T04:19:27Z")

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How exactly do you know that your regular expression doesn’t match?  
It’s more likely your program is matching, but that your output is not  
going  
where you expect. Cron output goes to the user. Since you are running  
this  
as root, are you reading root’s mail?

Create a ruby program like, cron\_test.rb

if /.\*/.match(“myrandomstring”)  
raise “Matched”  
else  
raise “No match”  
end

and then in your crontab

\*/5 \* \* \* \* /path/to/ruby /other/path/to/cron\_test.rb

wait 10 minutes and then read root’s mail.

Ray