How can I convert uppercase to lowercase or the other way around in Bash? [duplicate]

Question

Possible Duplicate:
converting string to lower case in bash shell scripting

For example:

 echo *****Language translator*****
 echo please choose the language
 for Chinese enter c
 for French enter f

In a simple way I want to be able to recognize both C and c for Chinese; and the same thing for f and F, recognized as French.

Is there a way to convert everything to lower case?

Here part of the code:

if [ $language == c ];
then
echo "Enter the word to translate:"
read word_to_translate

Answer 1

You can use tr to switch the chars to lowercase/uppercase:

echo $language | tr '[A-Z]' '[a-z]'

Answer 2

You can use the following case-modifiers (from man bash):

${parameter^}      # Convert the first character in ${parameter} to uppercase
${parameter^^}     # Convert all characters in ${parameter} to uppercase
${parameter,}      # Convert the first character in ${parameter} to lowercase
${parameter,,}     # Convert all characters in ${parameter} to lowercase

So your code might look something like this:

# Read one character into $lang, with a nice prompt.
read -n 1 -p "Please enter c for Chinese, or f for French: " lang
if [ "${lang,,}" == "c" ]; then
  echo "Chinese"
elif [ "${lang,,}" == "f" ]; then
  echo "French"
else
  echo "I don't speak that language."
fi

Answer 3

Modern versions of tr have support for POSIX character classes [:upper:] and [:lower:]

tr -s '[:upper:]'  '[:lower:]' < inputfile > outputfile

All of the character classes are here:

http://ss64.com/bash/tr.html

Answer 4

I'd probably use a case statement, though there are other ways to do it:

read language
case "$language" in
([cC]) echo 'Chinese';;
([fF]) echo 'French';;
(*)    echo 'Unrecognized language abbreviation';;
esac

You could make a canonical assignment in the case if you need the values outside the switch:

read language
case "$language" in
([cC]) lingua='zh_tw'; echo 'Chinese';;
([fF]) lingua='fr_fr'; echo 'French';;
(*)    echo 'Unrecognized language abbreviation';;
esac