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.

Could you post a sample of your log file? I agree that the grep line could be causing the problems. If your input line is

and you pipe it to that grep command, you'll get the whole line, not only the integers.

Try echoing the $char variable just before entering the if:

This way you can verify what exactly is in $char. Another debugging method is to use the "set -x" command at the beginning of the script.

Edit: just noticed that rknichols already suggested the same, oh well...

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...

Thanks guys,

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.

here are the results of the debug

+ char=$'25064\001'
+ echo $'25064\001'
25064
+ [[ 25064 =~ ^[0-9]+$ ]]
+ echo 'error: Not a number !!!'
error: Not a number !!!
+ exit 1

So the odd thing is what is that \001 doing there ?
Otherwise it seems to give out 25064 as a number

How did you initialize $char?

I did not initialise $char.
Its basically used as something like below to grep the number from a logfile:
char=`tac logfile | grep "(1.)" |grep -E '[0-9]{1,4}' | head -1`

"\001" is octal 1, ascii character #1, SOH (start of heading). Perhaps it's in your log file?

That's initialization.

As rnikols said, grep returns the whole line, not just the number.

you should give us a usable sample to be able to help you to construct a usable solution.
Personally I suggest you to do the following:
no sed, no grep, not tac, no head and cut and a lot of different tricks, just a single awk (or perl/python/whatever)

From the other hand the error message is correct, you tried to compare a string which contained not only digits, but something else too.
awk will also ensure you have a valid number.

Thanks, I was thinking of a similar sample to the one I am facing for such log lines

(123456:789.123)-{ABCDE.12345=456789:1234:ABCD.FGHJK:1111-CVBN543TGYH10:4564611:12312:5645=POIJKJH}

(123456:890.456)-{POIU.12345=456711:567834:ABCD.FGHJK9:2223-YYN543TGYH10:46646PPOUY^^&%:5775=POIJKJH}

(123456:990.888)-{POIU.12775=456709:1234:ABCD.FGHJK8:223-YYN543TGUU%10:466PPOUY%^%11:10777975=POIJKJH}

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.

You can do that quite easily with sed: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.

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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.

I thought I'd have a look at what would happen if an '11:' also appeared near the start of the first rec
but when I ran your sed it still picks out the 2nd occurrence. I can't seem to figure out why
Could you elucidate?
Thx

Greediness,
Pretty dodgy to rely on it tho' ...