Convert camelCase to Underscores Using sed

This short post deals with converting strings of the form camelCase or CamelCase into camel_case, and vice versa. These are three different popular naming conventions for variable/function/class names.

Convert CamelCase or camelCase to camel_case:

sed -e 's/([A-Z])/_\l\1/g' file.txt
echo "camelCase" | sed -e 's/([A-Z])/_\l\1/g'

Convert camel_case to camelCase

sed -e 's/_([a-z])/\u\1/g' file.txt
echo "camel_case" | sed -e 's/_([a-z])/\u\1/g'

Convert camel_case to CamelCase:

sed -e 's/_([a-z])/\u\1/g' -e 's/^([a-z])/\u\1/g' file.txt
echo "camel_case" | sed -e 's/_([a-z])/\u\1/g' -e 's/^([a-z])/\u\1/g'

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