tr(1p) — Linux manual page

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.1‐2017, 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         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.1‐2017, 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         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.1‐2017, 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         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.1‐2017,
       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         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.

       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.1‐2017, 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 1003.1-2017, 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 .

IEEE/The Open Group               2017                            TR(1P)

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