tr utility copies the standard input
to the standard output with substitution or deletion of selected
The options are as follows:
- Complements the set of characters in string1; for instance, “-C ab” includes every character except for ‘a’ and ‘b’.
- The same as
-doption causes characters to be deleted from the input.
-soption squeezes multiple occurrences of the characters listed in the last operand (either string1 or string2) in the input into a single instance of the character. This occurs after all deletion and translation is completed.
In the first synopsis form, the characters in string1 are translated into the characters in string2 where the first character in string1 is translated into the first character in string2 and so on. If string1 is longer than string2, the last character found in string2 is duplicated until string1 is exhausted.
In the second synopsis form, the characters in string1 are deleted from the input.
In the third synopsis form, the characters in
string1 are compressed as described for the
In the fourth synopsis form, the characters in
string1 are deleted from the input, and the characters
in string2 are compressed as described for the
The following conventions can be used in string1 and string2 to specify sets of characters:
- Any character not described by one of the following conventions represents itself.
- A backslash followed by 1, 2, or 3 octal digits represents a character with that encoded value. To follow an octal sequence with a digit as a character, left zero-pad the octal sequence to the full 3 octal digits.
- A backslash followed by certain special characters maps to special values.
- <alert character>
- <carriage return>
- <vertical tab>
A backslash followed by any other character maps to that character.
- Represents the range of characters between the range endpoints, inclusively.
- Represents all characters belonging to the defined character class. Class
- <alphanumeric characters>
- <alphabetic characters>
- <blank characters>
- <control characters>
- <numeric characters>
- <graphic characters>
- <lower-case alphabetic characters>
- <printable characters>
- <punctuation characters>
- <space characters>
- <upper-case characters>
- <hexadecimal characters>
With the exception of the “upper” and “lower” classes, characters in the classes are in unspecified order. In the “upper” and “lower” classes, characters are entered in ascending order.
For specific information as to which ASCII characters are included in these classes, see isalnum(3), isalpha(3), and related manual pages.
- Represents all characters or collating (sorting) elements belonging to the same equivalence class as equiv. If there is a secondary ordering within the equivalence class, the characters are ordered in ascending sequence. Otherwise, they are ordered after their encoded values. An example of an equivalence class might be “c” and “ch” in Spanish; English has no equivalence classes.
- Represents n repeated occurrences of the character represented by #. This expression is only valid when it occurs in string2. If n is omitted or is zero, it is interpreted as large enough to extend the string2 sequence to the length of string1. If n has a leading zero, it is interpreted as an octal value; otherwise, it's interpreted as a decimal value.
tr utility exits 0 on success,
and >0 if an error occurs.
The following examples are shown as given to the shell:
Create a list of the words in file1, one per line, where a word is taken to be a maximal string of letters.
$ tr -cs "[:alpha:]" "\n" < file1
Translate the contents of file1 to upper-case.
$ tr "[:lower:]" "[:upper:]" < file1
Strip out non-printable characters from file1.
$ tr -cd "[:print:]" < file1
tr utility is compliant with the
IEEE Std 1003.1-2008 (“POSIX.1”)
specification, except that the
-C option behaves the
same as the
-c option since
tr is not locale-aware.
System V has historically implemented character ranges using the syntax “[c-c]” instead of the “c-c” used by historic BSD implementations and standardized by POSIX. System V shell scripts should work under this implementation as long as the range is intended to map in another range, i.e., the command “tr [a-z] [A-Z]” will work as it will map the ‘[’ character in string1 to the ‘[’ character in string2. However, if the shell script is deleting or squeezing characters as in the command “tr -d [a-z]”, the characters ‘[’ and ‘]’ will be included in the deletion or compression list, which would not have happened under an historic System V implementation. Additionally, any scripts that depended on the sequence “a-z” to represent the three characters ‘a’, ‘-’, and ‘z’ will have to be rewritten as “a\-z”.
tr utility has historically not
permitted the manipulation of NUL bytes in its input and, additionally, has
stripped NUL's from its input stream. This implementation has removed this
behavior as a bug.
tr utility has historically been
extremely forgiving of syntax errors: for example, the
-s options were
ignored unless two strings were specified. This implementation will not
permit illegal syntax.
It should be noted that the feature wherein the last character of string2 is duplicated if string2 has less characters than string1 is permitted by POSIX but is not required. Shell scripts attempting to be portable to other POSIX systems should use the “[#*]” convention instead of relying on this behavior.