SHELL

bash transform uppercase to lowercase

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'

bash make string variable uppercase

scriptName=${0^^}

bash convert string to uppercase

var=hello #For Bash Version higher than 4.3.33 try these
echo ${var''} #Uppercase whole string
HELLO
echo ${var'} #Uppercase only first char of string
Hello
var2=BYE
echo ${var2,} #Lowercase whole string
bye
echo ${var2,,} #Lowercase only first char of string
bYE
echo $var | tr 'a-z' 'A-Z' #For lower versions of Bash just use tr command
HELLO

Bash - Convert a string from uppercase to lowercase

$ echo "$a" | tr '[:upper:]' '[:lower:]'
hi all

shell uppercase lowercase

# Basic syntax:
awk '{print tolower(string)}'
awk '{print toupper(string)}'

# Example usage:
awk '{print tolower($0)}' input_file
# This prints every row ($0) converted to lowercase

awk '{print toupper($3)}' input_file
# This would print the third field ($3) converted to uppercase

convert capital letters to lowercase in shell script

x="HELLO"
echo $x  # HELLO

y=${x,,}
echo $y  # hello

z=${y^^}
echo $z  # HELLO

how to compare a character to uppercase in bash script

echo "enter a char"
read c

if [[ $c == [A-Z] ]];
then
    echo "upper"
elif [[ $c == [a-z] ]];
then
    echo "lower"
else 
    echo "Digit or special symbols!"
fi