How to Convert Bash String to Lowercase? [7 Methods]

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In Bash scripting, case conversion is important for case-sensitive comparison, pattern matching, and file and directory operations. So for an effective and efficient conversion of Bash string to lowercase, a clear concept of case conversion is essential.

To convert a Bash string to lowercase, check the following methods:

Dive into the article to learn these methods of how to convert a bash string to lowercase in detail.

Table of Contents

The basic and simple way to convert a string’s characters to lowercase is by using the tr command. There are some other commands like awk, sed which gives flexibility while converting multibyte characters. In this section, 7 methods will be discussed which have been mentioned earlier on how to convert a string to lowercase.

To convert a string to lowercase, you can use parameter expansion. Parameter expansion refers to retrieving and manipulating the value that is stored in the parameter or variable. By using parameter expansion with,,,,, you can convert the first character of a string to lowercase, as well as convert all the characters in the string to lowercase.

To convert all characters of a string to lowercase using,,, follow the below script:

Firstly the script declares a string into a variable namedoriginal_string. Then the script uses a bash parameter expansion syntax${original_string,,} which converts all the characters of the original_string to lowercase. Later, the echo command prints the converted output in the terminal.

From the output, you can see the script converted all the characters of the input string to lowercase.

To convert only the first character to lowercase, replace the,,with ,in the code that you have used earlier to convert all characters to lowercase. Check the code:

The "${original_string,}" converts the first character of the original_string to lowercase.

Here the script only converts the first character of the string to lowercase.

To convert a specific character using a pattern, check the following code:

Firstly the bash script declares a string named “string”. Here the ${string,H} checks if the first character of the string is H, then it will convert the found H to lowercase. After that, the ${string,,L} converts all the occurrences of the characterLto lowercase. Lastly, the ${string,,[STRING]} changes all the occurrences of any character in STRING to lowercase.

The script successfully converts the first character, a specific character, and a group of characters to lowercase.

Note: The use of ~ in parameter expansion allows you to switch the case of the first character, while ~~ switches the case of all characters. This results in a modification of the current character, alternating between lowercase and uppercase.

To convert the upper case character to a lower case character, you can use the tr command. In bash scripting, the tr command is used to translate and delete characters. Take a look at the following script to convert a string from upper case to lower case:

At first, the bash script declares a string in a variable namedOriginal_string. In the lowercase_string=$(echo "$Original_string" | tr '[:upper:]' '[:lower:]'), the | (pipe) symbol pipes the output of theechocommand to thetrcommand. Then the tr command matches the upper-case characters and replaces them with lowercase characters.

From the output you can see, that the script converts the characters from upper case to lower case.

While declaring a variable, if you use the -l attribute with declare command then it will convert any value of the declared variable to lowercase. To convert a string to lowercase using the declare command, check the following script:

At first, the bash script declares a string into a variable named str. Moreover, the script uses the -l option with the declare command which converts all the characters to lowercase. At last, the echo command prints the output of the str variable in the terminal.

The output shows that the declare command has converted the characters to lowercase.

To convert the case of a string to lowercase, you can use the awk command. The awk is a versatile command tool used for text processing, handling multi-byte characters, and especially for pattern matching and manipulation. The awk command uses a tolower function to change the case of the characters of a given string.

Here’s the script to convert the character of a string to lowercase using the awk command:

The script uses |(pipe) operator to take the output of theechocommand to theawkcommand. In the awk '{print tolower($0)}', the awk command converts the echo command output to lowercase using its function tolower. In tolower($0), the ($0) indicates the entire output from the pipe operator.

The script converts the characters to lowercase using the awk command with the tolower function.

The sed command is a simple yet very useful command for stream editors in bash scripting. The sed command uses a special sequence that includes backslashes and one of the following letters L, l, U, u, E. These sequences have a special meaning, like:

The sed command mainly uses these sequences for case conversion.

To convert a string to lowercase using the sed command, follow the script below:

Firstly in method 1, thesedcommand takes the output through the pipe operator. In the sed command \(.*\) captures the string and the\Lconverts the strings’ characters to lowercase. Later in method 2, the script uses's/.*/\L&/g'which also converts the characters to lowercase. It uses-gflag which globally replaces all the characters in the output.

From the output, you can see the inputs’ uppercase characters have converted to lowercase.

To convert a specific character to lowercase using the sed command, take a look at the following script:

In the $(echo "$Main_string" | sed -e 's/H/h/g' -e 's/W/w/g'), the pipe operator takes the output of theechocommand and pipes it as input to the sed command. Thesed command replaces the characterHwithhandWwithwglobally. At last, the bash script stores the modified string in the New_string variable.

The output shows that the script replaces the first character of the words from upper case to lower case.

In bash scripting, the Perl command provides a simple way to convert strings to lowercase. The Perl command reads each line of the input then uses the lc function to convert the input to lowercase and later it displays the modified output. To convert a string to lowercase using the Perl command, check the following script:

In theperl -necommand, the-noption makes the perl command process the input line by line and the -option executes the perl command in the terminal. Later, the 'print lc' syntax, prints the converted lowercase of the input characters using the lc function.

The output shows the script converts the uppercase characters B, L, and P to lowercase b, l, and p respectively.

To convert the case of a string to lowercase, you can also use the ASCII value of the characters and arithmetic operations. Here’s the script: