Hi guys,
New member here, also new student!
I'm just starting the Shell Programming, currently in chapter four in the Book in Unix, Linux, and OS X by Stephen G. Kochan & Patrick Wood (4th edition).
I'm needing a little help with other possible ways to shorten this shell command:
/[0-9][0-9][0-9][0-9][ \][0-9][0-9][0-9][0-9][0-9][0-9][ \][0-9][0-9][0-9][0-9][0-9]/
It's purpose is to bed used in ed with a file open with possible matches.
This question was presented as follows:
Using the Regular Expression techniques that we have discussed in class develop, test, and submit a regular expression that will identify each of the following patterns.
An American Express credit card number that fits the following format: 4 digits followed by a space followed by 6 digits followed by a space followed by 5 digits.
Any input or help would be greatly appreciated!
If not, I'm happy to be a member here! 
Thanks