sed

Remove specific char from string

# only first occurrence
echo "hell" | sed 's/l//'
hel

# all occurrences ('g' option)
echo "hell" | sed 's/l//g'
he

Print lines between two matching patterns

sed -n '/^pattern1/,${p;/^pattern2/q}'

Remove empty lines

sed '/^$/d' 

Only print match

sed -n "s/version=[\"']\(.*\)[\"']/\1/p" setup.py