It is ok; you could just try it out and check the file afterwards. If it looks ok, cat and the redirection must have done a good job.
Since this is nothing special to AIX think about posting such kind of question into one of the more appropriate forums next time please. No offense, but since this is a very basic question UNIX for Dummies Questions & Answers - The UNIX and Linux Forums would be a good choice for it next time.
If it goes deeper into shell scripting etc. you can also post in
Now consider I have a common header 'HEADER' and trailer 'TRAILER' in all the files and I want to have their header , trailer only once in the concatenated output file. Please advice how could that be done?
If you have the 'HEADER' at the first line and 'TRAILER' at the last line in all your files you can delete the those lines after merging the files with:
First we use a variable var wich is the number of the last line (wc -l < file).
Now we print every line except the line with HEADER if it isn't the first line and the line with TRAILER if it isn't the last line.