TR(1)

NAME
tr - translate characters

SYNOPSIS
tr [-cs] string1 string2
tr [-c] -d string1
tr [-c] -s string1
tr [-c] -ds string1 string2

DESCRIPTION
The tr utility copies the standard input to the standard output with substitution or deletion of selected characters.

The following options are available:

-c  Complements the set of characters in string1, that is -c ab includes every character except for ‘a’ and ‘b’.

-d  The -d option causes characters to be deleted from the input.

-s  The -s option 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 -s option.

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 -s option.

The following conventions can be used in string1 and string2 to specify sets of characters:

character
    Any character not described by one of the following conventions represents itself.

\octal
    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.

\character
    A backslash followed by certain special characters maps to special values.

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

    A backslash followed by any other character maps to that character.

c-c Represents the range of characters between the range endpoints, inclusively.

[:class:]
    Represents all characters belonging to the defined character class. Class names are:

    alnum alphanumeric characters
    alpha alphabetic characters
    blank blank characters
    cntrl control characters
    digit numeric characters
    graph graphic characters
    lower lower-case alphabetic characters
    print printable characters
    punct punctuation characters
    space space characters
    upper upper-case characters
    xdigit 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 ctype(3) and related manual pages.

[=equiv=]
    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.

[#*n]
    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 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.

EXIT STATUS
tr exits 0 on success, and 0 if an error occurs.

EXAMPLES
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

COMPATIBILITY
AT&T UNIX has historically implemented character ranges using the syntax “[c-c]” instead of the “c-c” used by historic BSD implementations and standardized by POSIX. AT&T UNIX 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 AT&T UNIX 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”.

The tr utility has historically not permitted the manipulation of NUL bytes in its input and, additionally, stripped NUL's from its input stream. This implementation has removed this behavior as a bug.

The tr utility has historically been extremely forgiving of syntax errors, for example, the -c and -s options were ignored unless two strings were specified. This implementation will not permit illegal syntax.

STANDARDS
The tr utility is expected to be p1003.2 compatible. 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.

BUGS
tr was originally designed to work with US-ASCII. Its use with character sets that do not share all the properties of US-ASCII, e.g., a symmetric set of upper and lower case characters that can be algorithmically converted one to the other, may yield unpredictable results.

tr should be internationalized.