– Copy fromLocal/ToLocal from/to S3:

$ bin/hadoop fs -copyToLocal s3://my-bucket/myfile.rb /home/hadoop/myfile.rb
$ bin/hadoop fs -copyFromLocal job5.avro s3://my-bucket/input

– Merge all the files from one folder into one single file:

$ hadoop jar ~/lib/emr-s3distcp-1.0.jar --src s3://my-bucket/my-folder/ --dest s3://my-bucket/logs/all-the-files-merged.log --groupBy '.*(*)' --outputCodec none

– Create directory on HDFS:

$ bin/hadoop fs -mkdir -p /user/ubuntu

– List HDFS directory:

bin/hadoop fs -ls /

– Put a file in HDFS:

bin/hadoop dfs -put localfile.txt /user/hadoop/hadoopfile

– Check HDFS filesystem utilization:

$ bin/hadoop dfsadmin -report

– Cat of file on HDFS:

$ bin/hadoop  dfs -cat /user/ubuntu/RESULTS/part-00000

More commands:

http://hadoop.apache.org/docs/r0.18.3/hdfs_shell.html