TR(P) POSIX Programmer's Manual TR(P)
tr - translate characters
tr [-c | -C][-s] string1 string2
tr -s [-c | -C] string1
tr -d [-c | -C] string1
tr -ds [-c | -C] string1 string2
The tr utility shall copy the standard input to the standard output with substitution or deletion of selected characters. The options
specified and the string1 and string2 operands shall control translations that occur while copying characters and single-character collat-
The tr utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-c Complement the set of values specified by string1. See the EXTENDED DESCRIPTION section.
-C Complement the set of characters specified by string1. See the EXTENDED DESCRIPTION section.
-d Delete all occurrences of input characters that are specified by string1.
-s Replace instances of repeated characters with a single character, as described in the EXTENDED DESCRIPTION section.
The following operands shall be supported:
Translation control strings. Each string shall represent a set of characters to be converted into an array of characters used for
the translation. For a detailed description of how the strings are interpreted, see the EXTENDED DESCRIPTION section.
The standard input can be any type of file.
The following environment variables shall affect the execution of tr:
LANG Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all the other internationalization variables.
Determine the locale for the behavior of range expressions and equivalence classes.
Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments) and the behavior of character classes.
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
Determine the location of message catalogs for the processing of LC_MESSAGES .
The tr output shall be identical to the input, with the exception of the specified transformations.
The standard error shall be used only for diagnostic messages.
The operands string1 and string2 (if specified) define two arrays of characters. The constructs in the following list can be used to spec-
ify characters or single-character collating elements. If any of the constructs result in multi-character collating elements, tr shall
exclude, without a diagnostic, those multi-character elements from the resulting array.
Any character not described by one of the conventions below shall represent itself.
octal Octal sequences can be used to represent characters with specific coded values. An octal sequence shall consist of a backslash fol-
lowed by the longest sequence of one, two, or three-octal-digit characters (01234567). The sequence shall cause the value whose
encoding is represented by the one, two, or three-digit octal integer to be placed into the array. If the size of a byte on the sys-
tem is greater than nine bits, the valid escape sequence used to represent a byte is implementation-defined. Multi-byte characters
require multiple, concatenated escape sequences of this type, including the leading '' for each byte.
The backslash-escape sequences in the Base Definitions volume of IEEE Std 1003.1-2001, Table 5-1, Escape Sequences and Associated
Actions ( '\' , 'a' , '' , 'f' , '
' , '
' , ' ' , 'v' ) shall be supported. The results of using any other character,
other than an octal digit, following the backslash are unspecified.
c-c In the POSIX locale, this construct shall represent the range of collating elements between the range endpoints (as long as neither
endpoint is an octal sequence of the form octal), inclusive, as defined by the collation sequence. The characters or collating ele-
ments in the range shall be placed in the array in ascending collation sequence. If the second endpoint precedes the starting end-
point in the collation sequence, it is unspecified whether the range of collating elements is empty, or this construct is treated as
invalid. In locales other than the POSIX locale, this construct has unspecified behavior.
If either or both of the range endpoints are octal sequences of the form octal, this shall represent the range of specific coded values
between the two range endpoints, inclusive.
Represents all characters belonging to the defined character class, as defined by the current setting of the LC_CTYPE locale cate-
gory. The following character class names shall be accepted when specified in string1:
alnum blank digit lower punct upper
alpha cntrl graph print space xdigit
In addition, character class expressions of the form [: name:] shall be recognized in those locales where the name keyword has been given a
charclass definition in the LC_CTYPE category.
When both the -d and -s options are specified, any of the character class names shall be accepted in string2. Otherwise, only character
class names lower or upper are valid in string2 and then only if the corresponding character class ( upper and lower, respectively) is
specified in the same relative position in string1. Such a specification shall be interpreted as a request for case conversion. When [:
lower:] appears in string1 and [: upper:] appears in string2, the arrays shall contain the characters from the toupper mapping in the
LC_CTYPE category of the current locale. When [: upper:] appears in string1 and [: lower:] appears in string2, the arrays shall contain the
characters from the tolower mapping in the LC_CTYPE category of the current locale. The first character from each mapping pair shall be in
the array for string1 and the second character from each mapping pair shall be in the array for string2 in the same relative position.
Except for case conversion, the characters specified by a character class expression shall be placed in the array in an unspecified order.
If the name specified for class does not define a valid character class in the current locale, the behavior is undefined.
Represents all characters or collating elements belonging to the same equivalence class as equiv, as defined by the current setting
of the LC_COLLATE locale category. An equivalence class expression shall be allowed only in string1, or in string2 when it is being
used by the combined -d and -s options. The characters belonging to the equivalence class shall be placed in the array in an unspec-
x*n Represents n repeated occurrences of the character x. Because this expression is used to map multiple characters to one, it is only
valid when it occurs in string2. If n is omitted or is zero, it shall be interpreted as large enough to extend the string2-based
sequence to the length of the string1-based sequence. If n has a leading zero, it shall be interpreted as an octal value. Otherwise,
it shall be interpreted as a decimal value.
When the -d option is not specified:
* Each input character found in the array specified by string1 shall be replaced by the character in the same relative position in the
array specified by string2. When the array specified by string2 is shorter that the one specified by string1, the results are unspeci-
* If the -C option is specified, the complements of the characters specified by string1 (the set of all characters in the current charac-
ter set, as defined by the current setting of LC_CTYPE , except for those actually specified in the string1 operand) shall be placed in
the array in ascending collation sequence, as defined by the current setting of LC_COLLATE .
* If the -c option is specified, the complement of the values specified by string1 shall be placed in the array in ascending order by
* Because the order in which characters specified by character class expressions or equivalence class expressions is undefined, such
expressions should only be used if the intent is to map several characters into one. An exception is case conversion, as described pre-
When the -d option is specified:
* Input characters found in the array specified by string1 shall be deleted.
* When the -C option is specified with -d, all characters except those specified by string1 shall be deleted. The contents of string2 are
ignored, unless the -s option is also specified.
* When the -c option is specified with -d, all values except those specified by string1 shall be deleted. The contents of string2 shall be
ignored, unless the -s option is also specified.
* The same string cannot be used for both the -d and the -s option; when both options are specified, both string1 (used for deletion) and
string2 (used for squeezing) shall be required.
When the -s option is specified, after any deletions or translations have taken place, repeated sequences of the same character shall be
replaced by one occurrence of the same character, if the character is found in the array specified by the last operand. If the last operand
contains a character class, such as the following example:
tr -s '[:space:]'
the last operand's array shall contain all of the characters in that character class. However, in a case conversion, as described previ-
ously, such as:
tr -s '[:upper:]' '[:lower:]'
the last operand's array shall contain only those characters defined as the second characters in each of the toupper or tolower character
pairs, as appropriate.
An empty string used for string1 or string2 produces undefined results.
The following exit values shall be returned:
0 All input was processed successfully.
>0 An error occurred.
CONSEQUENCES OF ERRORS
The following sections are informative.
If necessary, string1 and string2 can be quoted to avoid pattern matching by the shell.
If an ordinary digit (representing itself) is to follow an octal sequence, the octal sequence must use the full three digits to avoid ambi-
When string2 is shorter than string1, a difference results between historical System V and BSD systems. A BSD system pads string2 with the
last character found in string2. Thus, it is possible to do the following:
tr 0123456789 d
which would translate all digits to the letter 'd' . Since this area is specifically unspecified in this volume of IEEE Std 1003.1-2001,
both the BSD and System V behaviors are allowed, but a conforming application cannot rely on the BSD behavior. It would have to code the
example in the following way:
tr 0123456789 '[d*]'
It should be noted that, despite similarities in appearance, the string operands used by tr are not regular expressions.
Unlike some historical implementations, this definition of the tr utility correctly processes NUL characters in its input stream. NUL char-
acters can be stripped by using:
tr -d '