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TR(1P)                     POSIX Programmer's Manual                    TR(1P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (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 IEEE Std 1003.1-2001, Section 12.2, Utility Syn-
       tax 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  DESCRIP-
              TION 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  inter-
              preted, 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 IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for  the  prece-
              dence 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  exam-
              ple,  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  writ-
              ten 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 follow-
       ing 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. If the size of a byte on the system 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.

       \character
              The backslash-escape sequences in the Base Definitions volume of IEEE Std 1003.1-2001, 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 unspec-
              ified.

       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 col-
              lation  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:

        * 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 unspecified.


        * If the -C option is specified, the complements of the characters specified by string1 (the set of all  char-
          acters  in the current character set, as defined by the current setting of LC_CTYPE,  except for those actu-
          ally 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  expres-
          sions  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  con-
       version, 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  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 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 stan-
           dard 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 accommoda-
       tions  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  recog-
       nized 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  ele-
       ments  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 func-
       tionality  equivalent  to the -c option specified in IEEE Std 1003.1-2001.  This meant that historical practice
       of being able to specify tr -d\200-\377 (which would delete all bytes with the  top  bit  set)  would  have  no
       effect because, in the C locale, bytes with the values octal 200 to octal 377 are not characters.

       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.  IEEE Std 1003.1-2001 specifies that octal sequences always  refer  to  single
       byte binary values.

FUTURE DIRECTIONS
       None.

SEE ALSO
       sed

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  Issue  6,  Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The
       Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan-
       dard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                               TR(1P)