tr

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(1) 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. 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:

c

Any character c 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
cntrl	Control characters
digit	Numeric characters
graph	Graphic characters
lower	Lowercase alphabetic characters
print	Printable characters
punct	Punctuation characters
space	Space characters
upper	Uppercase 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.

[=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.

[c*n]

Represents n repeated occurrences of the character represented by c. 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 is interpreted as a decimal value.

The tr(1) utility 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 uppercase:

tr [:lower:] [:upper:] < file1

Strip out non-printable characters from file1:

tr -cd [:print:] < file1

Perform (or undo) a rot13 transformation on text in file1:

tr [A-Ma-mN-Zn-z] [N-Zn-zA-Ma-m] < file1

COMPATIBILITY

System V has historically implemented character ranges using the syntax [c-c] instead of the c-c used by historic Berkeley Software Distribution (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. That is, the command tr [a-z] [A-Z] will work, as it will map the [ character in string1 to the [ character in string2. If the shell script is deleting or squeezing characters, however, 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.

The tr(1) 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(1) 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.