gistfile1.txt

#!/bin/bash
#
# A git hook for automatically running commands
# based on the name of files modified in the
# previous changeset
# 
# To install as a post-merge hook (on `git pull`):
# $ cp hook.sh .git/hooks/post-merge && chmod 755 $_
#
# To install as a post-checkout hook (changing branches):
# $ cp hook.sh .git/hooks/post-checkout && chmod 755 $_
#

KEYWORDS=( 'requirements' 'paver' )

# Check if we're in a virtualenv
python -c "import sys; sys.real_prefix" &> /dev/null

# Check if keywords in changed files list
if [ $? -eq 0 ]; then
	for MATCH in "$KEYWORDS"
	do
		git diff --name-only HEAD@{1} HEAD | grep -q $MATCH
		if [ $? -eq 0 ]; then
			paver update
			exit
		fi
	done
fi

What is the result of line 17?

sys.real_prefix is only set inside virtualenvs, an exception looking up a non-existent attribute causes a non-zero exit code (and skips the paver command).