Linux TR Command Examples

tr is an UNIX utility for translating, or deleting, or squeezing repeated characters. It will read from STDIN and write to STDOUT.
tr stands for translate.

Syntax

The syntax of tr command is:

$ tr [OPTION] SET1 [SET2]

Translation

If both the SET1 and SET2 are specified and ‘-d’ OPTION is not specified, then tr command will replace each characters in SET1 with each character in same position in SET2.

1. Convert lower case to upper case

The following tr command is used to convert the lower case to upper case

$ tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
thegeekstuff
THEGEEKSTUFF

The following command will also convert lower case to upper case

$ tr [:lower:] [:upper:]
thegeekstuff
THEGEEKSTUFF

You can also use ranges in tr. The following command uses ranges to convert lower to upper case.

$ tr a-z A-Z
thegeekstuff
THEGEEKSTUFF

2. 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.

$ tr '{}' '()' < inputfile > outputfile

The above command will read each character from “inputfile”, translate if it is a brace, and write the output in “outputfile”.

3. Translate white-space to tabs

The following command will translate all the white-space to tabs

$ echo "This is for testing" | tr [:space:] '\t'
This is for testing

4. Squeeze repetition of characters using -s

In Example 3, we see how to translate space with tabs. But if there are two are more spaces present continuously, then the previous command will translate each spaces to a tab as follows.

$ echo "This   is   for testing" | tr [:space:] '\t'
This   is   for testing

We can use -s option to squeeze the repetition of characters.

$ echo "This   is   for testing" | tr -s [:space:] '\t'
This is for testing

Similarly you can convert multiple continuous spaces with a single space

$ echo "This  is  for testing" | tr -s [:space:] ' '
This is for testing

5. Delete specified characters using -d option

tr can also be used to remove particular characters using -d option.

$ echo "the geek stuff" | tr -d 't'
he geek suff

To remove all the digits from the string, use

$ echo "my username is 432234" | tr -d [:digit:]
my username is

Also, if you like to delete lines from file, you can use sed d command.

6. 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 username is 432234" | tr -cd [:digit:]
432234

7. Remove all non-printable character from a file

The following command can be used to remove all non-printable characters from a file.

$ tr -cd [:print:] < file.txt

8. Join all the lines in a file into a single line

The below command will translate all newlines into spaces and make the result as a single line.

$ tr -s '\n' ' ' < file.txt