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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.

SEE ALSO

       sed

       The Base Definitions volume of POSIX.1‐2017, Table 5-1, Escape  Sequences  and  Associated
       Actions, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1-2017, Standard for Information Technology -- Portable  Operating  System  Interface
       (POSIX),  The  Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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
       Standard, 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 .

       Any  typographical  or  formatting errors that appear in this page are most likely to have
       been introduced during the conversion of the source files to man page  format.  To  report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .