upper- to lower-case on first column only in bash

Question

How do I change in bash only the first column into lower case? for example: ABC|DEF|GHI to abc|DEF|GHI

thanks

Answer 1

echo "ABC|DEF|GHI" | sed 's/\([A-Z]*\)\|/\L\1/'

outputs:

abc|DEF|GHI

Answer 2

awk -F"|" '{l = $0; sub($1, "", l); print tolower($1) l}' yourFile