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From "Olga Natkovich (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-58) parameterized Pig scripts
Date Tue, 08 Apr 2008 17:57:24 GMT

    [ https://issues.apache.org/jira/browse/PIG-58?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12586909#action_12586909
] 

Olga Natkovich commented on PIG-58:
-----------------------------------

In reply to last comments from Pi:

>>I am not sure but seems like all parser we have do that.I think others throw ParseException.


I checked - they throw both.

>>Here is comment on static structure:- Having getHash() and setHash() in both PigFileParser
and ParamLoader pointing to UtilFunctions.param_val is a kind of weird. If you try to substitute
vars multiple times in the same JVM, this can lead to side effects (I don't know if such scenarios
exist).  I think for the sake of clarity and reusability, UtilFunctions.param_val should be
separated as non-static member in a new ParamSubstituteContext class. PigFileParser and ParamLoader
then accept the context as constructor parameter.

Ok, I will look into making UtilFunctions a class without static and just pass it around.



> 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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