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From "Olga Natkovich (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-58) parameterized Pig scripts
Date Wed, 06 Feb 2008 00:57:08 GMT

    [ https://issues.apache.org/jira/browse/PIG-58?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12565977#action_12565977

Olga Natkovich commented on PIG-58:

This is in response to comment https://issues.apache.org/jira/browse/PIG-58?focusedCommentId=12565959#action_12565959

>> 1. The parameter usage notation seems to arcane
Hopefully, the new proposal to use #define to declare all variables addresses this issue

>> 2. "-param" key seems redundant and will cause confusion
I usually prefer explicit rather than implicit specifications. Also, the -param approach separates
pigs command line namespace from user parameter one. But I could go either way on this.

>> 3.  We need an ability to specify "DFS working directory" for the whole Pig job.
There is already way in pig to do that by issuing CD command

>> 4. Need to specify the precedence rules
I thought I already specified this in the proposal. Please, let me know which parts are unclear.

>> 5. Can parameters be used in RHS of declare?

My plan was to avoid it for the initial release to keep things simple since most of the use
cases I saw did not need that. However, I don't think it would be difficult to implement so
we can put that in.

> parameterized Pig scripts
> -------------------------
>                 Key: PIG-58
>                 URL: https://issues.apache.org/jira/browse/PIG-58
>             Project: Pig
>          Issue Type: New Feature
>            Reporter: Olga Natkovich
> 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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