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From "Alan Gates (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-58) parameterized Pig scripts
Date Tue, 08 Apr 2008 17:35:25 GMT

    [ https://issues.apache.org/jira/browse/PIG-58?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12586897#action_12586897
] 

Alan Gates commented on PIG-58:
-------------------------------

[Alan before] 1) Dryrun isn't a good name for the command line option. It's far to generic.
Knowing nothing about parameter substitution and looking at the usage statement of pig I'd
assume that dryrun meant that pig was going to parse my query but not run it. I would suggest
a name like preproc or preproconly

[Olga] I was hoping that we would extend dryrun over time to include things that you were
talking about. I did not mean it to stay parameter substitution specific. What do you think?

Seems fine.  We should put in a comment articulating that in the command line option.

[Alan before] 2) Why did we choose to put all of the data for the unit tests in separate files
in a test/data directory? To date the approach has been to have the
tests themselves generate the data they need on the fly. There are pros and cons to switching,
but I think we should discuss and have a policy of how unit tests handle their data before
we start adding a directory with a lot of files in it.

[Olga] This is how the test cases were created when they were given to me. SInce I did not
have strong oppinion and did not have time to redo them I left them as is. I am not really
sure that we need a policy on this. What are your concerns with different tests doing what
makes most sense for the kind of things they are testing? Let me know if you think it is ok
to leave it as is or if you think that it needs to be reworked before committing the changes.

I guess I like having one way to do things instead of 3 (does that mean I'm more of python
programmer than perl programmer?).  But it isn't worth delaying getting this in for.

[Alan before] 5) PigFileParser.jj doesn't skip over commented lines in the pig code. It should
ignore anything on a line after -

[Olga] The logic is to not change any lines including comments that don't have parameters
to be substituted. Grun parser will skip the comments.

I was referring to that fact that it will do substitutions in comments.  If we had comments
that could be terminated, this could lead to strange behavior (consider C
style /* comment */ comments and then defining a parameter that contained */).  But our comments
are currently to line end only (--) so it's should be fine.



> parameterized Pig scripts
> -------------------------
>
>                 Key: PIG-58
>                 URL: https://issues.apache.org/jira/browse/PIG-58
>             Project: Pig
>          Issue Type: New Feature
>            Reporter: Olga Natkovich
>         Attachments: PIG-58_v1.patch, PIG-58_v2
>
>
> This feature has been requested by several users and would be very useful in conjunction
with streaming. The feature would allow pig script to include parameters that are replaced
at run time. For instance, if your script needs to run on a daily basis over the data of the
previous day, you would be able to use the script and providing a date as a run-time parameter
to it.
> Example:
> =======
> Pig script myscript.pig:
> A = load '/data/mydata/%date%';
> B = filter A by $0>'5';
> .....
> Pig command line:
> pig -param date='20080110' myscript.pig
> Proposed interface and implementation:
> Interface:
> =======
> (0) Substitution will be only supported with pig script files.
> (1) Parameters are specified on the command line via -param <param>=<val>
construct. Multiple parameters can be specified. They are applied to the script in the order
they are specified on the command line
> (2) Default values for the parameters can be specified within the script via decare statement:
> decare <param>=<value>
> (3) Withint the script the parameter will be enclosed in %%. \% can be used te escape.
> Implementation:
> ============
> Use preprocessor to do the substitution. The preprocessor would be invoced by Main before
grunt is instanciated and do the following:
> - create a new file in temp location
> - build a hash of parameters from command line and declare statement
> - for each line in the original script
>   if this is a declare line, skip it
>   else for each unescaped pattern %<identifie>% look for a match in the hash. Replace,
if found.  Write the line to the temp file.
> - pass the temp file to grunt.

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