Flush Memcache or only prefixed entries from a command line

memcache.sh

#!/usr/bin/env bash

MEMCACHE_PID=$(\pgrep -f memcache)
MEMCACHE_HOST="127.0.0.1"
MEMCACHE_PORT="11211"

if [ -n "${MEMCACHE_PID}" ]; then
  # @todo Do we have an ability to use passwordless "sudo"?
  DATA=$(\sudo \netstat -plunt | \grep "${MEMCACHE_PID}" | \awk '{print $4}' | \head -n1)

  if [ -n "${DATA}" ]; then
    MEMCACHE_HOST="${DATA%%:*}"
    MEMCACHE_PORT="${DATA##*:}"
  fi
fi

memcache_command()
{
  \echo -e "$1\nquit\n" | \nc -q2 "${MEMCACHE_HOST}" "${MEMCACHE_PORT}"
}

memcache_clear()
{
  \echo "[INFO] Clearing Memcache at ${MEMCACHE_HOST}:${MEMCACHE_PORT}..."
  memcache_command "flush_all"
}

memcache_clear_by_prefix()
{
  if [ -n "$1" ]; then
    local PREFIX="$1"
    local COUNTER=0

    \echo "[INFO] Clearing Memcache entries prefixed by the \"${PREFIX}\" at ${MEMCACHE_HOST}:${MEMCACHE_PORT}..."

    for SLAB_ID in $(\seq 1 $(memcache_command "stats items" | \tail -n2 | \head -n1 | \awk -F ':' '{print $2}')); do
      for KEY in $(memcache_command "stats cachedump ${SLAB_ID} 0" | \awk '{print $2}'); do
        if [[ -n "${KEY}" && "${KEY}" =~ ^${PREFIX} ]]; then
          memcache_command "delete ${KEY}"> /dev/null 2>&1
          ((COUNTER++))
        fi
      done
    done

    \echo "[INFO] ${COUNTER} entries removed."
  else
    \echo "[WARN] Memcache key prefix is not set so nothing was cleared."
  fi
}

Useful Drupal-related usage:

# Do not use "drush vget" because it's bootstrap Drupal which may lead to
# facing a fatal error which we trying to avoid by clearing the Memcache.
# Also, "drsuh vset" may contain warnings/errors in "stdout" and in this
# case prefix will not be correct.
memcache_clear_by_prefix "$(\drush sql-connect | \awk -F '--database=' '{print $2}' | \awk '{print $1}')"