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That grep is returning the whole line that contains the match, not just the part that matches. Maybe you have a line that looks like it contains just a number, but any trailing white space will be included. You need to include the "-o" (--only-matching) option to ensure that just the part of the line that matches is returned.
It would help if your "Not a number" message included the string (wrapped in quotes) that was rejected.
A remark in addition to rknichols' comment about grep: To debug your program, make ample use of echo, writing the contents of the variables in question to the screen. You can also switch debugging on and off using set -x and set +x, so that you see what happens in crucial parts of your program.
Had you done that, you would have seen that $char is indeed not a number and not wasted your time writing a post.
Edit: Looks like this is at least the 3rd time this suggestion is made...
Last edited by berndbausch; 11-10-2015 at 10:45 PM.
I would love to post a sample of the log file, but unfortunately its "classified". Hence I gave the example above just to illustrate. All I can say its a bunch of text, numbers and special characters bunched up together. Besides the tac and grep and head commands I actually had to use sed and cut commands to "pluck out" the numbers I wanted. But unfortunately depends on the time it also plucks out text and special characters. Hence the need to compare using regex to see if its numbers - which I want then to print it out. If its text and something else, then discard.
oh thanks berndbausch for the set -x suggestion, I was wondering ways to debug. I will give that a try.
I am trying to pick out the numbers after "11:" So In the first line I want the numbers 123 from "11:123" and the second line I want 5678 from "11:5678" and the third I want 107779 from "11:107779" As you can see the "11:" jumps in various positions as the log progresses but as example in the same 3 positions randomly as the logs progresses. Not sure how I can achieve that with just awk. That's why I was using a bunch of tools like tac, sed, cut ,etc to pick out the latest one whenever I run the script. But I'm happy to explore any options.
The "-r" option says to use extended regular expressions. The "-n" inhibits the default printing of all lines. The expression looks for lines that contain "11:" followed by a string of one or more digits and possibly followed by more characters, replaces the entire line with just that string of digits from the parenthesized sub-expression, and prints the result.
Many thanks rknichols! It worked ! I tested many times and worked flawless so far, when the numbers moved from 4 digits to 5 digits and was correct each time. Thanks , now I can proceed with the rest of the script.