Change directory to PostgreSQL version and pg_log (or where you store the log files)
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cd /var/lib/pgsql/9.3/data/pg_log/

List CSV logs older than 29 days
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find *.csv -mtime +29 -exec ls {} \;

Truncate CSV logs older than 15 days
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find *.csv -mtime +15 -exec rm {} \;