# tr

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## NAME



           tr — translate characters
    


## SYNOPSIS



           tr **[** -c|-C**] [** -s**]**_string1 string2_
    
           tr -s **[** -c|-C**]**_string1_
    
           tr -d **[** -c|-C**]**_string1_
    
           tr -ds **[** -c|-C**]**_string1 string2_
    


## DESCRIPTION



           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 collating elements.
    


## OPTIONS



           The _tr_ utility shall conform to the Base Definitions volume of
           POSIX.1‐2017, _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.
    


## OPERANDS



           The following operands shall be supported:
    
           _string1_ , _string2_
                     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.
    


## STDIN



           The standard input can be any type of file.
    


## INPUT FILES



           None.
    


## ENVIRONMENT VARIABLES



           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 POSIX.1‐2017, _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.
    
           _LC_COLLATE_
                     Determine the locale for the behavior of range
                     expressions and equivalence classes.
    
           _LC_CTYPE_  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.
    
           _LC_MESSAGES_
                     Determine the locale that should be used to affect the
                     format and contents of diagnostic messages written to
                     standard error.
    
           _NLSPATH_   Determine the location of message catalogs for the
                     processing of _LC_MESSAGES_.
    


## ASYNCHRONOUS EVENTS



           Default.
    


## STDOUT



           The _tr_ output shall be identical to the input, with the exception
           of the specified transformations.
    


## STDERR



           The standard error shall be used only for diagnostic messages.
    


## OUTPUT FILES



           None.
    


## EXTENDED DESCRIPTION



           The operands _string1_ and _string2_ (if specified) define two arrays
           of characters. The constructs in the following list can be used to
           specify 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.
    
           _character_ 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> followed 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. Multi-byte
                     characters require multiple, concatenated escape
                     sequences of this type, including the leading
                     <backslash> for each byte.
    
           \_character_
                     The <backslash>-escape sequences in the Base Definitions
                     volume of POSIX.1‐2017, _Table 5-1_ , _Escape Sequences and_
                     _Associated Actions_ (**'\\'** , **'\a'** , **'\b'** , **'\f'** , **'\n'** , **'\r'** ,
                     **'\t'** , **'\v'**) shall be supported. The results of using any
                     other character, other than an octal digit, following
                     the <backslash> are unspecified. Also, if there is no
                     character following the <backslash>, the results 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 elements in the
                     range shall be placed in the array in ascending
                     collation sequence. If the second endpoint precedes the
                     starting endpoint 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.
    
           [:_class_ :] Represents all characters belonging to the defined
                     character class, as defined by the current setting of
                     the _LC_CTYPE_ locale category. 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.
    
           [=_equiv_ =] 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 unspecified order.
    
           [_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:
    
            *  If _string2_ is present, 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_.  If
               the array specified by _string2_ is shorter that the one
               specified by _string1_ , or if a character occurs more than once
               in _string1_ , the results are unspecified.
    
            *  If the **-C** option is specified, the complements of the
               characters specified by _string1_ (the set of all characters in
               the current character 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 binary value.
    
            *  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 previously.
    
           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
           previously, 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.
    


## EXIT STATUS



           The following exit values shall be returned:
    
            0    All input was processed successfully.
    
           >0    An error occurred.
    


## CONSEQUENCES OF ERRORS



           Default.
    
           _The following sections are informative._
    


## APPLICATION USAGE



           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 ambiguity.
    
           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 POSIX.1‐2017,
           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 characters can be stripped by using:
    
               tr -d '\000'
    


## EXAMPLES



            1. The following example creates a list of all words in **file1** one
               per line in **file2** , where a word is taken to be a maximal
               string of letters.
    
                   tr -cs "[:alpha:]" "[\n*]" <file1 >file2
    
            2. The next example translates all lowercase characters in **file1**
               to uppercase and writes the results to standard output.
    
                   tr "[:lower:]" "[:upper:]" <file1
    
            3. This example uses an equivalence class to identify accented
               variants of the base character **'e'** in **file1** , which are
               stripped of diacritical marks and written to **file2**.
    
                   tr "[=e=]" "[e*]" <file1 >file2
    


## RATIONALE



           In some early proposals, an explicit option **-n** was added to
           disable the historical behavior of stripping NUL characters from
           the input. It was considered that automatically stripping NUL
           characters from the input was not correct functionality.  However,
           the removal of **-n** in a later proposal does not remove the
           requirement that _tr_ correctly process NUL characters in its input
           stream. NUL characters can be stripped by using _tr_ **-d** '\000'.
    
           Historical implementations of _tr_ differ widely in syntax and
           behavior. For example, the BSD version has not needed the bracket
           characters for the repetition sequence. The _tr_ utility syntax is
           based more closely on the System V and XPG3 model while attempting
           to accommodate historical BSD implementations. In the case of the
           short _string2_ padding, the decision was to unspecify the behavior
           and preserve System V and XPG3 scripts, which might find
           difficulty with the BSD method.  The assumption was made that BSD
           users of _tr_ have to make accommodations to meet the syntax defined
           here. Since it is possible to use the repetition sequence to
           duplicate the desired behavior, whereas there is no simple way to
           achieve the System V method, this was the correct, if not
           desirable, approach.
    
           The use of octal values to specify control characters, while
           having historical precedents, is not portable. The introduction of
           escape sequences for control characters should provide the
           necessary portability. It is recognized that this may cause some
           historical scripts to break.
    
           An early proposal included support for multi-character collating
           elements.  It was pointed out that, while _tr_ does employ some
           syntactical elements from REs, the aim of _tr_ is quite different;
           ranges, for example, do not have a similar meaning (``any of the
           chars in the range matches'', _versus_ ``translate each character in
           the range to the output counterpart''). As a result, the
           previously included support for multi-character collating elements
           has been removed. What remains are ranges in current collation
           order (to support, for example, accented characters), character
           classes, and equivalence classes.
    
           In XPG3 the [:_class_ :] and [=_equiv_ =] conventions are shown with
           double brackets, as in RE syntax. However, _tr_ does not implement
           RE principles; it just borrows part of the syntax.  Consequently,
           [:_class_ :] and [=_equiv_ =] should be regarded as syntactical elements
           on a par with [_x_ *_n_], which is not an RE bracket expression.
    
           The standard developers will consider changes to _tr_ that allow it
           to translate characters between different character encodings, or
           they will consider providing a new utility to accomplish this.
    
           On historical System V systems, a range expression requires
           enclosing square-brackets, such as:
    
               tr '[a-z]' '[A-Z]'
    
           However, BSD-based systems did not require the brackets, and this
           convention is used here to avoid breaking large numbers of BSD
           scripts:
    
               tr a-z A-Z
    
           The preceding System V script will continue to work because the
           brackets, treated as regular characters, are translated to
           themselves.  However, any System V script that relied on **"a‐z"**
           representing the three characters **'a'** , **'-'** , and **'z'** have to be
           rewritten as **"az-"**.
    
           The ISO POSIX‐2:1993 standard had a **-c** option that behaved
           similarly to the **-C** option, but did not supply functionality
           equivalent to the **-c** option specified in POSIX.1‐2008.
    
           The earlier version also said that octal sequences referred to
           collating elements and could be placed adjacent to each other to
           specify multi-byte characters. However, it was noted that this
           caused ambiguities because _tr_ would not be able to tell whether
           adjacent octal sequences were intending to specify multi-byte
           characters or multiple single byte characters. POSIX.1‐2008
           specifies that octal sequences always refer to single byte binary
           values when used to specify an endpoint of a range of collating
           elements.
    
           Earlier versions of this standard allowed for implementations with
           bytes other than eight bits, but this has been modified in this
           version.
    


## FUTURE DIRECTIONS



           None.
    


* * *