Question 19673 in Amazon Web Sevices Question posted in
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Bash – Extract region from AWS arn

Very simple task: extract the region from an AWS arn.

Example:

arn:aws:lambda:eu-west-2:12345678912:layer:my-awsome-layer:3

I need to extract eu-west-2

I have a working regex for this: ^(?:[^:]+:){3}([^:]+).*

I tried this command, but it returns the entire string:

echo "arn:aws:lambda:eu-west-2:12345678912:layer:my-awsome-layer:3" | grep -oP '^(?:[^:]+:){3}([^:]+).*'

output: arn:aws:lambda:eu-west-2:12345678912:layer:my-awsome-layer:3

What is wrong with the above?

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3

Answers


  1. Chosen as BEST ANSWER
    0

    Thanks for @Inian for the quick and good answer in the comments:

    echo "arn:aws:lambda:eu-west-2:12345678912:layer:my-awsome-layer:3" | cut -d':' -f4

    Does the trick.

    output: eu-west-2


  2. 0

    A more flexible approach:

    grep -oP 'w{2}-w+-d+'
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  3. 0

    You get back the whole line because you are using .* at the end of the pattern.

    As you are using grep -oP you can make use of K to forget what is matched so far:

    grep -oP '^(?:[^:]+:){3}K[^:]+'

    An alternative using awk setting : as the field separator and printing the fourth field:

    awk -F: '{print $4}'

    Or using sed and replace with capture group 2, as capture group 1 is repeated 3 times:

    sed 's/^([^:]+:){3}([^:]+).*/2/'

    The examples will output:

    eu-west-2
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