Shell Script: Convert Lowercase to Uppercase

Objective: Convert the contents of a file or the contents of a shell string variable from lowercase to uppercase.

There are too many ways to do that. Let’s take a look at a few of them. Throughout this article, you can assume that the file “lowercase.txt” is the input file and the file “uppercase.txt” is the output file.

Lowercase to Uppercase with tr

The first method is to use the tr command. The below command will read the text found in file lowercase.txt, convert the text to upper case and write the output to file uppercase.txt.

$ tr '[:lower:]' '[:upper:]' < lowercase.txt > uppercase.txt

1	$ tr '[:lower:]' '[:upper:]' < lowercase.txt > uppercase.txt

If the input is stored in a variable, use the echo command and pipe the output to tr command. So, if the variable $LCASE has a string in lowercase, convert it using the syntax below.

$ echo $LCASE | tr '[:lower:]' '[:upper:]'

1	$ echo $LCASE \| tr '[:lower:]' '[:upper:]'

Lowercase to Uppercase with awk

Use the following syntax to convert the contents of the file using awk.

$ awk '{print toupper($0)}' < lowercase.txt > uppercase.txt

1	$ awk '{print toupper($0)}' < lowercase.txt > uppercase.txt

To convert a string variable ($LCASE) from lowercase to uppercase, use the following syntax.

$ echo $LCASE | awk '{print toupper($0)}'

1	$ echo $LCASE \| awk '{print toupper($0)}'

Lowercase to Uppercase with dd

Yes, the dd command is also able to perform the case conversion. Perform the case conversion using the following syntax.

$ dd if=lowercase.txt of=uppercase.txt conv=ucase

1	$ dd if=lowercase.txt of=uppercase.txt conv=ucase

To convert a string variable, and print the result on the screen, use the following syntax.

$ echo $LCASE | dd conv=ucase 2> /dev/null

1	$ echo $LCASE \| dd conv=ucase 2> /dev/null

Lowercase to Uppercase with sed

This works on GNU sed only as it uses GNU sed extension. Perform case conversion by using the following syntax.

$ sed -e 's/\(.*\)/\U\1/' lowercase.txt > uppercase.txt

1	$ sed -e 's/$.*$/\U\1/' lowercase.txt > uppercase.txt

The ‘\1’ matches the whole line since the whole regular expression is within parenthesis. The special sequence ‘\U’ changes text to uppercase.

For a string variable containing lowercase characters, convert it to uppercase with sed by using the following syntax.

$ echo "$LCASE" | sed -e 's/\(.*\)/\U\1/'

1	$ echo "$LCASE" \| sed -e 's/$.*$/\U\1/'

Lowercase to Uppercase with Bash Shell

Bash shell allows case modification through parameter expansion. To change the string variable ($LCASE) from lowercase to uppercase, use the following syntax.

$ echo "${LCASE^^}"

1	$ echo "${LCASE^^}"

The “^^” expansion changes the characters to uppercase.

Mohamed Ibrahim

ibrahim = { interested_in(unix, linux, android, open_source, reverse_engineering); coding(c, shell, php, python, java, javascript, nodejs, react); plays_on(xbox, ps4); linux_desktop_user(true); }