Jenkinspipeline showing "illegal string body character after dollar sign"

I'm trying to download the latest file from one s3 bucket and checking whether the same file exist in a different s3 bucket (different aws account). If it doesn't exist, the pipeline shud copy the file to the 2nd s3 bucket.

def exec(String commandString) {
  return sh(script: ${commandString}, returnStdout: true).trim()
}

pipeline {
  agent {
    docker {
      image 'xxx.dkr.ecr.us-west-2.amazonaws.com/abc/base-image:xxxx.xxx'
      registryUrl 'https://xxx.dkr.ecr.us-west-2.amazonaws.com'
      registryCredentialsId 'ecr:us-west-2:xxx'
      label 'docker-preemptive'
           }
  }
parameters {
    string(
      defaultValue: 'abc',
      description: 'src Bucket Name',
      name: 'src_bucket')
    string(
      defaultValue: 'abc_src_path',
      description: 'S3 source path',
      name: 'src_base_location')
    string(
      defaultValue: 'xyz',
      description: 'DST S3 bucket name',
      name: 'dst_bucket')
    string(
      defaultValue: 'xyz_dst_path',
      description: 'Destination path',
      name: 'dst_base_location')
    string(
      defaultValue: 'file_location',
      description: '',
      name: 'file_location')
  }
  environment {
    AWS_DEFAULT_REGION = "us-west-2"
    SRC_LATEST_S3_FILE = ''
    DST_LATEST_S3_FILE = ''
  }
    stage ("SRC s3 bucket file download") {
      steps {
        script {
          withCredentials([[
            $class: 'AmazonWebServicesCredentialsBinding',
            credentialsId: "abc_src_iam_credentials",
            accessKeyVariable: 'ABC_S3_ACCESS_KEY_ID',
            secretKeyVariable: 'ABC_S3_SECRET_ACCESS_KEY'
          ]]) { 
            def cmd = "aws s3 ls s3://${params.src_bucket}/${params.src_base_location}/${file_location}/ | sort | tail -n 1 | awk '{print $4}'"
            echo "$cmd"
            echo "Fetching latest filename from SRC s3"
            env.SRC_LATEST_S3_FILE= exec(cmd)
            echo env.SRC_LATEST_S3_FILE
            
            //SRC latest file validation
            if (env.SRC_LATEST_S3_FILE == '' ) {
              echo "No file exist in SRC S3"
            }
            else {
              echo "Downloading latest file to local path"
              def src_cp_cmd = '''aws s3 cp s3://${params.src_bucket}/${params.src_base_location}/${file_location}/${env.SRC_LATEST_S3_FILE} ${env.SRC_LATEST_S3_FILE}'''
              exec(src_cp_cmd)
            }
          }
        }
      }
    }
    stage ( "s3 File validation") {
      when {
        not {
          expression { env.SRC_LATEST_S3_FILE.isEmpty() }
        }
      }
      steps {
        script {
          withCredentials([[
            $class: 'AmazonWebServicesCredentialsBinding',
            credentialsId: "xyz-dst-s3-creds",
            accessKeyVariable: 'S3_DST_ACCESS_KEY_ID',
            secretKeyVariable: 'S3_DST_SECRET_ACCESS_KEY'
          ]]) { 
            def cmd1 = '''aws s3 ls "s3://${params.dst_bucket}/${params.dst_base_location}/${file_location/" | sort | tail -n 1 | awk '{print $4}' '''
            env.DST_LATEST_S3_FILE = exec(cmd1)
            
            //src and dest file validation
            if ( ${env.SRC_LATEST_S3_FILE} == ${env.DST_LATEST_S3_FILE} ) {
              echo "File already exists in DST bucket"
            }
            else {
              echo "Unable to find the latest file in s3 DST bucket"
              echo "Copying latest SRC file from local path to DST-S3 bucket"
              def dst_cp_cmd = '''aws s3 cp ${env.SRC_LATEST_S3_FILE} "s3://${params.dst_bucket}/${params.dst_base_location}/${file_location}/${env.SRC_LATEST_S3_FILE}"'''
              exec(dst_cp_cmd)
            } 
          }
        }
      }
    }
  }
}

When this above pipeline is executed, the pipeline job is failing with below ERROR

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
WorkflowScript: 82: illegal string body character after dollar sign;
   solution: either escape a literal dollar sign "\$5" or bracket the value expression "${5}" @ line 50, column 131.
   sort |tail -n 1 |awk '{print $4}'"""

Any guidance to fix this in the right way will be very much appreciated. Thank you !!!