PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       tr — translate characters

SYNOPSIS         top

       tr [−c|−C] [−s] string1 string2

       tr −s [−c|−C] string1

       tr −d [−c|−C] string1

       tr −ds [−c|−C] string1 string2

DESCRIPTION         top

       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         top

       The tr utility shall conform to the Base Definitions volume of
       POSIX.1‐2008, 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         top

       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         top

       The standard input can be any type of file.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       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.1‐2008, 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         top

       Default.

STDOUT         top

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

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       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.1‐2008, 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.

       cc       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         top

       The following exit values shall be returned:

        0    All input was processed successfully.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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.1‐2008, 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         top

        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         top

       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. This meant that historical
       practice of being able to specify tr −cd\000−\177 (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. 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         top

       None.

SEE ALSO         top

       sed(1p)

       The Base Definitions volume of POSIX.1‐2008, Table 5-1, Escape
       Sequences and Associated Actions, Chapter 8, Environment Variables,
       Section 12.2, Utility Syntax Guidelines

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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 .

IEEE/The Open Group                 2013                              TR(1P)

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