Extracting substring in bash script

Question

I am not that good at bash scripting. I have a requirement to extract a substring between two words of a string. I tried different ways. Could some one help me pls?

This is my text "RegionName": "eu-west-1", "LatestAmiId": "ami-0ebfeadd9ccacfbb2",

Remember the the quotes and comma are the part of String. I need to extract the AMI ID alone, Means text between "LatestAmiId": " and ",

Any help pls?

This looks like a section of JSON, have you considered using a tool like jq to work with JSON objects in scripts? It could prove to be much easier than specifically grabbing a substring — Will Barnwell
– Will Barnwell, Commented Jul 11, 2018 at 22:43

Will Barnwell · Accepted Answer · 2018-07-11 22:57:57Z

2

Assuming you have this string stored in a variable name input_text you can get the AmiId using sed like this

ami_id=$(echo "$input_text" | sed -e 's/.*LatestAmiId": "//' -e 's/",$//')

this uses two different sed scripts:

s/.*LatestAmiId": "// replaces all text up to and including LatestAmiId": " with nothing
s/",$// replaces the ", at the end of the line with nothing

As I mentioned in comments, jq is a tool that I have found really helpful when working with JSON objects in bash scripts. Since your input string looks like a section out of a json response from an AWS api, I highly recommend using a json tool rather than a regex to extract this information.

edited Jul 11, 2018 at 22:57

answered Jul 11, 2018 at 22:48

Will Barnwell

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6 Comments

ASChakkalakal Over a year ago

Okay. Thanks Will .

ASChakkalakal Over a year ago

I will try jq. Meanwhile the regex not replacing the first part of string . After the replacement I get "RegionName": "eu-west-1 ami-0ebfeadd9ccacfbb2 . I just needed the ami id

Will Barnwell Over a year ago

hmmm, it worked for me as expected, replaced the entire thing. Is it possible that there are newline characters in your string?

Will Barnwell Over a year ago

PCRE . matches everything except newlines by default

ASChakkalakal Over a year ago

No there is no new line char. It not replacing "RegionName": "eu-west-1 .

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