exact match a string in a variable with a string in another

Question

I have a sentence which is nothing but a string variable with words separated by spaces .

I have another variable which contains a word . What I wanted is to find exact matching of the word in the variable containing the sentence . I have tried this :

read -p "enter the word to match " STR # STR contains VVDNSG 

#this DUP_SG_NAME_PUBLIC variable contains a string which consists of few words 
DUP_SG_NAME_PUBLIC=$(aws ec2 describe-security-groups \
  --query 'SecurityGroups[*].{GroupName:GroupName}' \
  --output text) 

if [[ $DUP_SG_NAME_PUBLIC =~ $STR ]]
then 
echo "true"
else 
echo "false"
fi

Problem Here I have provided "VVDN" as string but I have to match "VVDNSG" but this code works for both . Even for VVDN and VVDNSG which is understandable .

What I want to do
I want to find exact match that is if given VVDNSG as STR value it should print true or else false even with VVDN and I want that to do the comparison with variables not with literal strings .

I have tried few examples googling most of them either tell you to find match in a file or hardcode the string comparison.

Seems like a case with an exact match first and a wildcard match second might be what you want. — jww
– jww, Commented Aug 4, 2018 at 14:36

João Miranda · Accepted Answer · 2018-08-04 15:27:40Z

3

Your STR works as a regex. So, to use it as an exact match, explicitly mark the beginning with ^and the end with $:

STR="^VVDN$"

Then the if condition will be true only for exact matches of STR in DUP_SG_NAME_PUBLIC.

Update: Actually, I think what you want is somewhat different - you have a sentence containing words separated by spaces (you didn't mention a termination character) and you want to match one of the words, only if it is an exact match. Let's assume it will be an exact match if it has a space after the word or if it is at the end of the sentence.

In that case, your regex could be:

STR="VVDN($| )"

Is this what you meant?

edited Aug 4, 2018 at 15:27

answered Aug 4, 2018 at 14:46

João Miranda

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3 Comments

0decimal0 Over a year ago

Yes you are right , I have a sentence containing words stored in variable and I want to match one of the words only if it is an exact match . Let me check your solution .Problem is I take input from the user to be stored in STR variable . I know that ^ and $ mark the begin and end but only if I could use them in user input . I have edited the question.

0decimal0 Over a year ago

I am a little sketchy on awk and sed , I don't know if these tools could work here .

João Miranda Over a year ago

After storing the input from the user you can always append something to it. For example, you can do STR="${STR}($| )". If you want the exact match to be extended to the whole word, which means the match could happen at the beginning of the sentence or when there's a space before the match, you could change it to STR="(^| )${STR}($| )".

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