Change between multiple DB2 instances in the same server. It has two modes, interactive or with parameter. The script is written in bash for DB2 9.7 but it can be used in any previous or more recent version.

db2env

#!/bin/bash

# Changes the environment to the given DB2 instance.
#
# You need to 'source' this command in order to change the environement.
# To ease the process, you can create a function per instance in the .profile.
#
# function i01 { . ${CHINS} db2inst1 ; }
#
# To configure, you just need to change the DB2 path.
#
# 20130601 A. Gomez (AngocA) - Creation script.
# 20130617 A. Gomez (AngocA) - Modification after refactoring to get close to oraenv.

# DB2 path
DB2_DIR=/opt/ibm/db2/9.7/

#set -x

changeInstance () {
  # Instance name (lower case)
  INSTANCE=$1
  PROFILE_DIR="~/${INSTANCE}/sqllib/db2profile"
  RETURN=0

  if [[ -f ${PROFILE_DIR} ]] ; then
    . ${PROFILE_DIR}
  else
    echo "DB2 profile does not exist for the given instance"
    RETURN=-1
  fi
  # Disconnect any existing connection.
  CONN=$(db2 connect | awk '/Local database alias/ {print $5}')
  if [[ ! -z ${CONN} ]] ; then
    echo "Disconnected from ${CONN}"
  fi

  # Terminates the previous db2bp (DB2 backend process)
  db2 terminate > /dev/null
  echo "Current instance ${DB2INSTANCE}"
  return ${RETURN}
}

# Instance name (lower case)
INSTANCE=$1

if [[ -f ${DB2_DIR}/bin/db2greg ]] ; then
  DB2GREG=${DB2_DIR}/bin/db2greg
else
  echo "DB2 binaries (DB2GREG) location unknown."
  exit -1
fi

# Checks if an instance name was given.
if [[ -z ${INSTANCE} ]] ; then
  PS3='Please select an instance: '

  INDEX=0
  while read LINE ; do
    CLIENTS[$INDEX]="$LINE"
    INDEX=$(($INDEX+1))
  done < <(${DB2GREG} -dump | awk -F, '/^I,/ {print $4}')

  QUIT=Quit
  CLIENTS[$INDEX]=${QUIT}

  select OPT in "${CLIENTS[@]}"
  do
    if [[ ${OPT} != ${QUIT} ]] ; then
      INST_VALID=$(${DB2GREG} -dump | grep I, | grep ,${OPT},\/)
     # Checks if the instance exists in the server
      if [[ -z ${INST_VALID} ]] ; then
        echo "Invalid instance: ${INSTANCE}"
      else
        changeInstance ${OPT}
        if [[ $? -eq 0 ]] ; then
           break
        fi
      fi
    else
      break
    fi
  done
else
  INST_VALID=$(${DB2GREG} -dump | grep I, | grep ,${INSTANCE},)
  # Checks if the instance exists in the server
  if [[ -z ${INST_VALID} ]] ; then
    echo "Invalid instance: ${INSTANCE}"
  else
    changeInstance ${INSTANCE}
  fi
fi

This is the evolution of chins. This is more dynamic.