Sed: would like to return an error for empty string

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# 1  
Old 04-13-2020
Sed: would like to return an error for empty string

There are actually two things that I want to do:

1. Detect if there is a 3 digit number and if so return an error (working)
2. Detect if there is an empty string and return an error if so (not working)

I would like to do 1 & 2 using the sed command only once; I'm trying to do things correctly and efficiently.

I have so far:
echo "" | sed -n -r '/[0-9]{3}/{q100}; //{q100}'; echo $?

(For newbies: -n quiets text output, -r allows for GNU program to do true regex, {q100} returns error '100', '$?' is the last returned result)

The result is 0, which is not what I want as the string is empty. My attempt is the portion '//{q100}', but I can see that it is difficult to test against nothing-quite perplexing actually.
# 2  
Old 04-13-2020
Try testing for "start-of-line nothing end-of-line":

echo "" | sed -n -r '/[0-9]{3}/{q100}; /^$/{q200}'; echo $?

And, wouldn't it make sense to have different codes for different errors?
This User Gave Thanks to RudiC For This Post:
# 3  
Old 04-13-2020
Originally Posted by RudiC
Try testing for "start-of-line nothing end-of-line":

echo "" | sed -n -r '/[0-9]{3}/{q100}; /^$/{q200}'; echo $?

And, wouldn't it make sense to have different codes for different errors?
Indeed. I've just added them. Smilie

Such a simple solution. Thanks so much.
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