How to backup a datafile using rman?

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How to backup a datafile using rman?
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[oracle@wasiq ~]$ rman

Recovery Manager: Release 11.2.0.1.0 - Production on Fri Jan 10 21:18:03 2014

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RMAN> connect target /;

connected to target database: PROD (DBID=246965557)

RMAN> configure controlfile autobackup off;

using target database control file instead of recovery catalog
old RMAN configuration parameters:
CONFIGURE CONTROLFILE AUTOBACKUP ON;
new RMAN configuration parameters:
CONFIGURE CONTROLFILE AUTOBACKUP OFF;
new RMAN configuration parameters are successfully stored

RMAN> backup datafile 1;

Starting backup at 10-JAN-14
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=71 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00001 name=/d01/oracle/oradata/prod/system01.dbf
channel ORA_DISK_1: starting piece 1 at 10-JAN-14
channel ORA_DISK_1: finished piece 1 at 10-JAN-14
piece handle=/d01/oracle/flash_recovery_area/PROD/backupset/2014_01_10/o1_mf_nnndf_TAG20140110T211828_9f05ldfw_.bkp tag=TAG20140110T211828 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:25
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current control file in backup set
including current SPFILE in backup set
channel ORA_DISK_1: starting piece 1 at 10-JAN-14
channel ORA_DISK_1: finished piece 1 at 10-JAN-14
piece handle=/d01/oracle/flash_recovery_area/PROD/backupset/2014_01_10/o1_mf_ncsnf_TAG20140110T211828_9f05m6l7_.bkp tag=TAG20140110T211828 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 10-JAN-14

RMAN>