tr uppercase to lowercase code example

Example 1: tr lowercase uppercase

tr '[:lower:]' '[:upper:]'

Example 2: translate lower to upper in unix

Just use tr command to transform lowercase letters into uppercase as:
tr a-z A-Z < file.txt	#transforms letters into uppercase in a file
echo 'HELLO' | tr A-Z a-z	#Outputs: 'hello'

Example 3: tr replace

#Just define the replacement 
tr [to_be_replace] [replacement] file.txt
#For example
tr a-z A-Z file.txt