#!/bin/bash
s='"example1_policy" {
    name="example"
    policy=jsonencode(
        {
            Statement=[
                {
                    Action=[
                        s3:*
                    ]
                    Effect="Allow"
                },
            ]
            Version="2012-10-17"
        }
    )
}
"example2_policy" {
    name="example2"
    policy=jsonencode(
        {
            Statement=[
                {
                    Action=[
                        s3:*
                    ]
                    Effect="Allow"
                },
            ]
            Version="2012-10-17"
        }
    )
}
"example3_policy" {
    name="example3"
    policy=jsonencode(
        {
            Statement=[
                {
                    Action=[
                        s3:*
                    ]
                    Effect="Allow"
                },
            ]
            Version="2012-10-17"
        }
    )
}'
perl -0777 -pe 's/^(\h*policy=)[^()]*(\((?:[^()]++|(?2))*\))/$1<placehlder>/gm' <<< "$s"