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From "Olga Natkovich (JIRA)" <j...@apache.org>
Subject [jira] Created: (PIG-58) parameterized Pig scripts
Date Thu, 10 Jan 2008 22:28:33 GMT
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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