When you switch branch, run the `pod install`. install to `path/to/.git/hooks/`

post-checkout

#!/bin/sh

set -e

prev="$1"
new="$2"
branch_switch="$3"

if [ -z "$branch_switch" ] || [ $branch_switch -eq 0 ]; then
  exit 0 # this was a file checkout
fi

if [ "$prev" = "$new" ]; then
  exit 0 # this was same branch
fi

zero="0000000000000000000000000000000000000000"
if [ "$prev" = "$zero" ]; then
  exit 0 # this was a clone
fi

if [ -d $HOME/.rbenv ]; then
  export PATH="$HOME/.rbenv/bin:$PATH"
  eval "$(rbenv init -)"
fi

cd `git rev-parse --show-toplevel`

diff=`git diff $perv $new --name-only | grep Podfile`
if [ -f "$PWD/Podfile" ] && [ -n $diff ]; then
  echo 'run `pod install`'
  echo -e "`pod install`"
fi

$perv on line 29 seems to be wrong