Shell Programming and Scripting

There's a file whose date format for the year 2012 are currently in mddyyyy format that we are trying to change to mmddyyyy. Presuming that the grep command in the excerpt below is accurate, it looks like there are over forty-nine thousand records affected by the single-digit month format:

Code:

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grep -n ,[12][0-9][0-9]2012, filename | wc -l
49120
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Is there a way to append a zero to the beginning of those records without modifying the other text?

Moderator's Comments:

use Code Tags when you post any code or data samples

Can you post a sample of the file?

This should find the first bad date as specified by your reg-ex, and add a zero. Non matching lines are left unchanged.

Code:

sed 's/,\([12][0-9][0-9]2012\),/,0\1,/'  orig-file >new-file