Puppet users - Aug 2013 - escape sequence within generate function

I''m looking for some help in getting the proper escape sequence within
the
generate function.
Ultimately what I''m trying to do is generate some random strings, store
them as variables, and use those variables to populate configuration files 
stored as templates.
I can get this to work when applying the template on the localhost, but it 
fails when applied via the puppet master.:
> $random_1 = generate("/bin/sh", "-c", "/bin/cat
/dev/urandom | /usr/bin/tr-
> dc ''a-z0-9'' | /usr/bin/fold -w 8 | /usr/bin/head -n 1 |
/usr/bin/tr -d
> ''\n''")

The closest I''ve come is to use:
> $random_1 = generate(''/bin/sh'', ''-c'',
''\"/bin/cat /dev/urandom | /usr/bin/
> tr -dc \''a-z0-9\'' | /usr/bin/fold -w 8 | /usr/bin/head -n
1 | /usr/bin/tr-d \''\n\''\"''
> )

This however ends up populating the variable with the following and appears 
to ignore the the "/usr/bin/tr -d ''\n''" as there are
line breaks inserted:
> /bin/sh: "/bin/cat: No such file or directory
>
What I''m really wanting (I think) to be executed on the puppet master
is
> "/bin/sh" "-c" "/bin/cat /dev/urandom |
/usr/bin/tr -dc ''a-z0-9'' |
> /usr/bin/fold -w 8 | /usr/bin/head -n 1 | /usr/bin/tr -d
''\n''"

Any help would be appreciated. 

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On Thursday, August 1, 2013 2:37:03 PM UTC-5, Jacob McCoy Wade
wrote:
>
> I''m looking for some help in getting the proper escape sequence
within the
> generate function.
> Ultimately what I''m trying to do is generate some random strings,
store
> them as variables, and use those variables to populate configuration files 
> stored as templates.
> I can get this to work when applying the template on the localhost, but it 
> fails when applied via the puppet master.:
>
>> $random_1 = generate("/bin/sh", "-c",
"/bin/cat /dev/urandom | /usr/bin/
>> tr -dc ''a-z0-9'' | /usr/bin/fold -w 8 | /usr/bin/head
-n 1 | /usr/bin/tr-d ''\n''"
>> )
>
>
> The closest I''ve come is to use:
>
>> $random_1 = generate(''/bin/sh'',
''-c'', ''\"/bin/cat /dev/urandom | /usr
>> /bin/tr -dc \''a-z0-9\'' | /usr/bin/fold -w 8 |
/usr/bin/head -n 1 | /usr
>> /bin/tr -d \''\n\''\"'')
>
>
> This however ends up populating the variable with the following and 
> appears to ignore the the "/usr/bin/tr -d ''\n''"
as there are line breaks
> inserted:
>
>> /bin/sh: "/bin/cat: No such file or directory
>>
>
>
So, that''s the wrong thing to do, because ''cat'' will
keep reading its input
until it reaches the end, which it never will in this case.  It may be that 
having ''head'' in the pipeline would rescue it by closing its
own input, but
you might end up with a bunch of stalled, orphaned processes.  You should 
instead use /bin/dd or some other command that allows you to limit the 
amount of data read from /dev/urandom.

But that brings us to the next problem: The output you see on the master 
appears to be telling you that the file you are trying to cat 
(/dev/urandom) does not exist there.  Possibly it''s there, but it or
its
parent directory is not readable by Puppet.  Unless you can sort that out, 
you will need an altogether different approach.

 
> What I''m really wanting (I think) to be executed on the puppet
master is
>
>> "/bin/sh" "-c" "/bin/cat /dev/urandom |
/usr/bin/tr -dc ''a-z0-9'' |
>> /usr/bin/fold -w 8 | /usr/bin/head -n 1 | /usr/bin/tr -d
''\n''"
>
>
> Any help would be appreciated. 
>

There is also a third, more fundamental problem: it is unlikely that you 
really want to do what you are trying to do.  If you generate a completely 
random component to a config file on every run, then that file will never 
match from one run to the next, so it will always be re-synced.  That is 
rarely the intent.  More often, you want different, random strings for each 
node, but you want those strings to be stable from run to run for any given 
node.  One way to achieve that might be to construct strings as the 
concatenation of a constant stem and a random number generated via
Puppet''s
built-in fqdn_rand() function.

Even if that would not be sufficient, I have trouble seeing why it makes 
sense to use generate() for this purpose.  It would be not only 
lighter-weight but also more flexible to use Ruby''s rand() function via
Puppet''s inline_template() function.  You could even use fqdn_rand() to
seed the Ruby RNG, so as to get a broader range of consistent pseudorandom 
values.  And, you would have as much control as you want over the random 
data -- such as, for instance, ensuring that it does not contain null (0) 
bytes.

As for the question in your title, to insert the literal two-character 
sequence ''\n'' into a double-quoted Puppet string, escape the
backslash by
doubling it: "... /usr/bin/tr -d ''\\n''".  (See 
http://docs.puppetlabs.com/puppet/3/reference/lang_datatypes.html#strings.) 
Note that only the outermost quotes affect what escape sequences are 
recognized; the inner single quotes in your string are just ordinary 
characters to Puppet.


John

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On Friday, August 2, 2013 6:43:01 AM UTC-7, jcbollinger
wrote:
>
>
>
> On Thursday, August 1, 2013 2:37:03 PM UTC-5, Jacob McCoy Wade wrote:
>>
>> The closest I''ve come is to use:
>>
>>> $random_1 = generate(''/bin/sh'',
''-c'', ''\"/bin/cat /dev/urandom | /usr
>>> /bin/tr -dc \''a-z0-9\'' | /usr/bin/fold -w 8 |
/usr/bin/head -n 1 | /usr
>>> /bin/tr -d \''\n\''\"'')
>>
>>
>> This however ends up populating the variable with the following and 
>> appears to ignore the the "/usr/bin/tr -d
''\n''" as there are line breaks
>> inserted:
>>
>>> /bin/sh: "/bin/cat: No such file or directory
>>>
>>
>>
> So, that''s the wrong thing to do, because ''cat''
will keep reading its
> input until it reaches the end, which it never will in this case.  It may 
> be that having ''head'' in the pipeline would rescue it by
closing its own
> input, but you might end up with a bunch of stalled, orphaned processes.  
> You should instead use /bin/dd or some other command that allows you to 
> limit the amount of data read from /dev/urandom.
>
> I was using head to close the input.  The other thing I can''t
quite make
sense of is why it works when I apply the module directly on the node, but 
not when using a puppet master.
 
> There is also a third, more fundamental problem: it is unlikely that you 
> really want to do what you are trying to do.  If you generate a completely 
> random component to a config file on every run, then that file will never 
> match from one run to the next, so it will always be re-synced.  That is 
> rarely the intent.  More often, you want different, random strings for each
> node, but you want those strings to be stable from run to run for any given
> node.  One way to achieve that might be to construct strings as the 
> concatenation of a constant stem and a random number generated via
Puppet''s
> built-in fqdn_rand() function.
>
> I was thinking that I could use "replace =>
''no''," within the module so
that puppet won''t re-sync the file every run.
 
> Even if that would not be sufficient, I have trouble seeing why it makes 
> sense to use generate() for this purpose.  It would be not only 
> lighter-weight but also more flexible to use Ruby''s rand()
function via
> Puppet''s inline_template() function.  You could even use
fqdn_rand() to
> seed the Ruby RNG, so as to get a broader range of consistent pseudorandom 
> values.  And, you would have as much control as you want over the random 
> data -- such as, for instance, ensuring that it does not contain null (0) 
> bytes.
>
> I''ve yet to use the inline_template() function and am not fluent
enough in
Ruby to know how to use the rand() function, but it sounds like it might be 
time to learn how :)
 
> As for the question in your title, to insert the literal two-character 
> sequence ''\n'' into a double-quoted Puppet string, escape
the backslash by
> doubling it: "... /usr/bin/tr -d ''\\n''".  (See 
> http://docs.puppetlabs.com/puppet/3/reference/lang_datatypes.html#strings.)
> Note that only the outermost quotes affect what escape sequences are 
> recognized; the inner single quotes in your string are just ordinary 
> characters to Puppet.
>
That helps me at least understand about escape sequencing in Puppet.  The 
other issue with using the generate() function is that I run in to either 
"Generators must be fully qualified" or "Generators can only
contain
alphanumerics, file separators, and dashes".  More proof that it''s
time to
give up on trying to make the generator() function work for this purpose.
Thanks for the help.

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On Friday, August 2, 2013 12:07:24 PM UTC-5, Jacob McCoy Wade
wrote:
>
>
>
> On Friday, August 2, 2013 6:43:01 AM UTC-7, jcbollinger wrote:
>>
>>
>>
>> On Thursday, August 1, 2013 2:37:03 PM UTC-5, Jacob McCoy Wade wrote:
>>>
>>> The closest I''ve come is to use:
>>>
>>>> $random_1 = generate(''/bin/sh'',
''-c'', ''\"/bin/cat /dev/urandom | /usr
>>>> /bin/tr -dc \''a-z0-9\'' | /usr/bin/fold -w 8 |
/usr/bin/head -n 1 | /usr
>>>> /bin/tr -d \''\n\''\"'')
>>>
>>>
>>> This however ends up populating the variable with the following and
>>> appears to ignore the the "/usr/bin/tr -d
''\n''" as there are line breaks
>>> inserted:
>>>
>>>> /bin/sh: "/bin/cat: No such file or directory
>>>>
>>>
>>>
>> So, that''s the wrong thing to do, because
''cat'' will keep reading its
>> input until it reaches the end, which it never will in this case.  It
may
>> be that having ''head'' in the pipeline would rescue it
by closing its own
>> input, but you might end up with a bunch of stalled, orphaned
processes.
>> You should instead use /bin/dd or some other command that allows you to
>> limit the amount of data read from /dev/urandom.
>>
>> I was using head to close the input.  The other thing I can''t
quite make
> sense of is why it works when I apply the module directly on the node, but 
> not when using a puppet master.
>

Like all Puppet functions, generate() runs on machine where the catalog is 
compiled, not on the one where it is applied, unless they are the same.  It 
appears that the master you are using does not have (a Puppet-accessible) 
/dev/urandom, whereas the target node has one that is accessible to the 
user as whom you are running ''puppet apply''.

 
>  
>
>> There is also a third, more fundamental problem: it is unlikely that
you
>> really want to do what you are trying to do.  If you generate a
completely
>> random component to a config file on every run, then that file will
never
>> match from one run to the next, so it will always be re-synced.  That
is
>> rarely the intent.  More often, you want different, random strings for
each
>> node, but you want those strings to be stable from run to run for any
given
>> node.  One way to achieve that might be to construct strings as the 
>> concatenation of a constant stem and a random number generated via
Puppet''s
>> built-in fqdn_rand() function.
>>
>> I was thinking that I could use "replace =>
''no''," within the module so
> that puppet won''t re-sync the file every run.
>

You could, though by doing so you give up the ability to have Puppet keep 
the file synced to your spec.  Replace => ''no'' is most
appropriately
applied to files that are expected to be modified in the course of their 
normal use, however, to prevent Puppet from clobbering the modifications.  
Inasmuch the only reason for using it here seems to be to facilitate using 
/dev/urandom as the source of randomness, and as using /dev/urandom for 
this purpose appears inferior in most ways to using Puppet''s and/or
Ruby''s
built-in sources of randomness, I really don''t see the point.


John

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