tr command in Unix/Linux with examples

The tr (translate) command in Linux is used to transform or delete specific characters from text input. It is commonly used for tasks like changing letter cases, removing unwanted characters, or compressing repeating characters.

• Reads input from standard input (stdin) or a file and outputs modified text.
• Can convert uppercase to lowercase or vice versa.
• Supports character replacement and range operations (e.g., [a-z], [A-Z]).

Example

Suppose we have a file named test.txt that contains both lowercase and uppercase text. We can use the tr command to convert all lowercase characters to uppercase.

cat test.txt

Output:

• To convert all lowercase letters to uppercase, use either of the following:

Syntax

It is often used together with pipes (|) or redirection (>>) to process the content of files in more complex ways.

tr [OPTION] SET1 [SET2]

Options

• -c : Applies the operation to characters not in the specified set (complements the set).
• -d : Deletes all characters in the first set from the output.
• -s : Replaces repeated occurrences of characters in set1 with a single occurrence.
• -t : Truncates set1 to match the length of set2 during translation.

Example 1: Using character ranges

cat test.txt | tr [a-z] [A-Z]

Output:

Example 2: Using predefined character classes

cat test.txt | tr [:lower:] [:upper:]

Output:

WELCOME TO
GEEKSFORGEEKS

Example 3: Using input redirection

tr [:lower:] [:upper:] < test.txt

Output:

WELCOME TO
GEEKSFORGEEKS

• [a-z] [A-Z] converts lowercase letters to uppercase.
• [:lower:] [:upper:] does the same but is more portable across systems.
• Input redirection < allows tr to read directly from a file without using cat.

tr Command Options

Here are the commonly used options in the tr command in Linux, along with examples and short explanations

Example 1. How to translate white-space characters to tabs

The following command translates all the white-space characters to tabs:

echo "Welcome To GeeksforGeeks" | tr [:space:] "\t"

Output:

Welcome    To    GeeksforGeeks

In the previous example we can also use redirection to provide intput for tr. Although this time we will use a here string for that:

tr [:space:] "\t" <<< "Welcome To GeeksforGeeks"

Output:

Welcome    To    GeeksforGeeks

Example 2. How to translate braces into parenthesis

You can also translate from and to a file. In this example we will translate braces in a file with parenthesis.

$ cat greekfile

Output:

{WELCOME TO} 
GeeksforGeeks

$ tr "{}" "()" <greekfile >newfile.txt

Output:

(WELCOME TO) 
GeeksforGeeks

The above command will read each character from “geekfile.txt”, translate if it is a brace, and write the output to “newfile.txt”.

Example 3. How to squeeze a sequence of repetitive characters using -s option

To squeeze repetitive occurrences of characters specified in a set use the -s option. This removes repeated instances of characters of the last SET specified. OR we can say that, you can convert multiple continuous spaces with a single space:

$ echo "Welcome    To    GeeksforGeeks" | tr -s " "

Output:

Welcome To GeeksforGeeks

And again, accomplish the same task but using a string here:

tr -s " " <<< "Welcome    To    GeeksforGeeks"

Output:

Welcome To GeeksforGeeks

Example 4. How to delete specified characters using -d option

To delete specific characters use the -d option. This option deletes characters in the first set specified.

echo "Welcome To GeeksforGeeks" | tr -d W

Output:

elcome To GeeksforGeeks

Or equivalently use:

tr -d W <<< "Welcome to GeeksforGeeks"

Output:

elcome To GeeksforGeeks

Example 5. To remove all the digits from the string

You can use:

echo "my ID is 73535" | tr -d [:digit:]

or

tr -d [:digit:] <<< "my ID is 73535"

Example 6. How to complement the sets using -c option

You can complement the SET1 using -c option. For example, to remove all characters except digits, you can use the following.

$ echo "my ID is 73535" | tr -cd [:digit:]

or

$ tr -cd [:digit:] <<< "my ID is 73535"

Output:

73535

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