TR command in Linux

tr stands for translate, which finds and replaces characters. It is good for manipulating text on the CLI. It has 2 mandatory sets, where SET1 translates into SET2 characters.

There are certain special character maps to special values.

• \a alert character
• \b backspace
• \f form-feed
• \n newline
• \r carriage return
• \t tab
• \v vertical tab

You have 2 options to run the tr command. In this article, I will be using option 1 most of the time but you are free to choose other options as well.

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# option 1
echo "Yafiz Abraham" | tr 'SET1' 'SET2'

# option 2
cat filename.txt | tr 'SET1' 'SET2'

To convert lower case letters into upper case letters.

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echo "hello world" | tr 'a-z' 'A-Z'
echo "hello world" | tr '[:lower:]' '[:upper:]'

To convert all upper case letters into lower case letters.

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echo "HELLO WORLD" | tr 'A-Z' 'a-z'
echo "HELLO WORLD" | tr '[:upper:]' '[:lower:]'

To remove spaces or any other characters, use -d flag which means delete.

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echo "hello world" | tr -d ' '
echo "hello world" | tr -d 'ld'

To find and replace any characters, use -s flag which means squeeze. Run the following command to remove all spaces and keep only a single space instead.

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echo "hello       world" | tr -s ' '
echo "hello       world" | tr -s '[:space:]'

You can also find spaces and replace them with a single hyphen.

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echo "hello       world" | tr -s ' ' '-'

You can also find a single space and replace it with multiple spaces or a single tab (2 or more spaces).

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echo "I want you to add more space" | tr -s ' ' '\t'

You can also find and replace a single character.

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echo "hello world" | tr -s "o" "H"

To find numbers and replace them with x characters.

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echo "HELLO 778df99 world 123aaa456" | tr '0-9' 'x'
echo "HELLO 778df99 world 123aaa456" | tr '[:digit:]' 'x'

Run the following command to find out numbers only from the given string.

• \n is adding a new line at the end of each statement.
• -c flag which means complement, so this flag makes sure that -d flag should remove everything except the given string (except numbers 0-9).

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echo "HELLO 778df99 world 123aaa456" | tr -cd '0-9\n'
echo "HELLO 778df99 world 123456" | tr -cd '[:digit:]\n'

To find out alphabets only from the given string either small letters and big letters.

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echo "HELLO 7789df9 world 123dfaa456" | tr -cd 'a-zA-Z\n'
echo "HELLO 778df99 world 123asdf456" | tr -cd '[:alpha:]\n'

To find out letters and digits only from the given string and remove whatever is left.

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echo "HELLO 77899 #$%as^#$ world 123456 +;.sdasdfasffQ@{as" | tr -cd 'a-zA-Z0-9\n'
echo "HELLO 77899 #$%^asdjw234#$ world 123456 +;.123Q@{" | tr -cd '[:alnum:]\n'