On Linux, we generally use the head/tail commands to preview the contents of a file. It helps in viewing a part of the file (to inspect the format for instance), rather than open up the whole file.
In the case of Amazon S3, it seems that there are only ls, cp, mv etc. commands I wanted to know if it is possible to view part of the file without downloading the entire file on my local machine using cp/GET.
You can specify a byte range when retrieving data from S3 to get the first N bytes, the last N bytes or anything in between. (This is also helpful since it allows you to download files in parallel – just start multiple threads or processes, each of which retrieves part of the total file.)
I don't know which of the various CLI tools support this directly but a range retrieval does what you want.
The AWS CLI tools ("aws s3 cp" to be precise) does not allow you to do range retrieval but s3curl (http://aws.amazon.com/code/128) should do the trick.(So does plain curl, e.g., using the --range parameter but then you would have to do the request signing on your own.)