tr Command

Purpose

Transforms characters or range of characters.

Syntax

To transform characters or sequence of characters:

tr [  -c | -cds | -cs | -C | -Cds | -Cs | -ds |  -s ] [  -A ] String1 String2

To delete characters or sequence of characters:

tr { -cd | -cs | -Cd | -Cs |  -d |  -s } [  -A ] String1

To define a range of characters for a specific locale:

[LANG=ll_RR] tr  -L {c1-cn C1-Cn} {c1c2c3c4c5c6…cn C1C2C3C4C5C6…Cn}

To delete a range of characters that is specified by the user:

[LANG=ll_RR] tr  -L {c1-cn C1-Cn}

Description

The tr command deletes or substitutes characters from standard input and writes the result to standard output. The tr command also defines a range of characters for a specific locale. The tr command performs the following types of operations depending on the strings specified by the String1 and String2 variable and depending on the flags specified by the user.

Transforming Characters

If String1 and String2 are both specified and the -d flag is not specified, the tr command replaces each character contained in String1 from the standard input with the character in the same position in String2.

Deleting Characters Using the -d Flag

If the -d flag is specified, the tr command deletes each character contained in String1 from standard input.

Removing Sequences Using the -s Flag

If the -s flag is specified, the tr command removes all but the first character in any sequence of a character string represented in String1 or String2. For each character represented in String1, the tr command removes all but the first occurrence of the character from standard output. For each character represented in String2, the tr command removes all but the first occurrence in a sequence of occurrences of that character in the standard output.

Defining a character range in the current locale environment

You can specify a character range for specific locales, code sets, and users by using the -L flag of the tr command. The tr command retains and recognizes the character range that you specified. The tr command uses this information to transform the characters to the mapped characters in the range. The character range c1-cn that is specified with the -L flag is mapped to characters c1c2c3c4c5c6...cn, and the specified character range C1-Cn is mapped to characters C1C2C3C4C5C6...Cn.

Special Sequences for Expressing Strings

The strings contained in the String1 and String2 variables can be expressed using the following conventions:

alnum      lower
alpha      print
blank      punct
cntrl      space
digit      upper
graph      xdigit

If a character is specified more than once in String1, the character is transformed into the character in String2 that corresponds to the last occurrence of the character in String1.

If the strings specified by String1 and String2 are not the same length, the tr command ignores the extra characters in the longer string.

Flags

Exit Status

This command returns the following exit values:

0

All input was processed successfully.

>0

An error occurred.

Examples

1. To transform braces into parentheses, enter the following command:

   tr '{}' '()' < textfile > newfile

   This transforms each { (left brace) to ( (left parenthesis) and each } (right brace) to ) (right parenthesis). All other characters remain unchanged.
2. To transform braces into brackets, enter the following command:

   tr '{}' '\[]' < textfile > newfile

   This transforms each { (left brace) to [ (left bracket) and each } (right brace) to ] (right bracket). The left bracket must be entered with a \ (backslash) escape character.
3. To transform lowercase characters to uppercase, enter the following command:

   tr 'a-z' 'A-Z' < textfile > newfile

4. To create a list of words in a file, enter the following command:

   tr -cs '[:lower:][:upper:]' '[\n*]' < textfile > newfile

   This transforms each sequence of characters other than lowercase letters and uppercase letters into a single newline character. The * (asterisk) causes the tr command to repeat the new line character enough times to make the second string as long as the first string.
5. To delete all NULL characters from a file, enter the following command:

   tr -d '\0' < textfile > newfile

6. To replace every sequence of one or more new lines with a single new line, enter the following command:

   tr -s '\n' < textfile > newfile

   OR

   tr -s '\012' < textfile > newfile

7. To replace every nonprinting character, other than valid control characters, with a ? (question mark), enter the following command:

   tr -c '[:print:][:cntrl:]' '[?*]' < textfile > newfile

   This scans a file created in a different locale to find characters that are not printable characters in the current locale.
8. To replace every sequence of characters in the <space> character class with a single # character, enter the following command:

   tr -s '[:space:]' '[#*]'

9. To define a character range for a specific locale, enter the following command:

   LANG=ES_ES tr -L a-z A-Z abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ

   This command defines the a-z and A-Z character ranges for the ES_ES (Spanish_Spain) locale.
10. To delete a character range for a specific locale, enter the following command:

    LANG=ES_ES tr -L a-z A-Z