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. tr — translate characters tr [−c|−C] [−s] string1 string2 tr −s [−c|−C] string1 tr −d [−c|−C] string1 tr −ds [−c|−C] string1 string2 The utility shall copy the standard input to the standard output with substitution or deletion of selected characters. The options specified and the and operands shall control translations that occur while copying characters and single‐ character collating elements. The utility shall conform to the Base Definitions volume of POSIX.1‐2008, The following options shall be supported: −c Complement the set of values specified by See the EXTENDED DESCRIPTION section. −C Complement the set of characters specified by See the EXTENDED DESCRIPTION section. −d Delete all occurrences of input characters that are specified by −s Replace instances of repeated characters with a single character, as described in the EXTENDED DESCRIPTION section. 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. The standard input can be any type of file. None. ‐2‐ The following environment variables shall affect the execution of LANG Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1‐2008, 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 Default. The output shall be identical to the input, with the exception of the specified transformations. The standard error shall be used only for diagnostic messages. None. The operands and (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, 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 ‐3‐ 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, (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 locale category. The following character class names shall be accepted when specified in alnum blank digit lower punct upper alpha cntrl graph print space xdigit In addition, character class expressions of the form [:shall be recognized in those locales where the keyword has been given a definition in the category. When both the and options are specified, any of the character class names shall be accepted in Otherwise, only character ‐4‐ class names or are valid in and then only if the corresponding character class (and respectively) is specified in the same relative position in Such a specification shall be interpreted as a request for case conversion. When [:appears in and [:appears in the arrays shall contain the characters from the mapping in the category of the current locale. When [:appears in and [:appears in the arrays shall contain the characters from the mapping in the category of the current locale. The first character from each mapping pair shall be in the array for and the second character from each mapping pair shall be in the array for 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 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 as defined by the current setting of the locale category. An equivalence class expression shall be allowed only in or in when it is being used by the combined and options. The characters belonging to the equivalence class shall be placed in the array in an unspecified order. [x*n] Represents repeated occurrences of the character Because this expression is used to map multiple characters to one, it is only valid when it occurs in If is omitted or is zero, it shall be interpreted as large enough to extend the sequence to the length of the sequence. If has a leading zero, it shall be interpreted as an octal value. Otherwise, it shall be interpreted as a decimal value. When the option is not specified: * If is present, each input character found in the array specified by shall be replaced by the character in the same relative position in the array specified by If the array specified by is shorter that the one specified by or if a character occurs more than once in the results are unspecified. * If the option is specified, the complements of the characters specified by (the set of all characters in the current character set, as defined by the current ‐5‐ setting of except for those actually specified in the operand) shall be placed in the array in ascending collation sequence, as defined by the current setting of * If the option is specified, the complement of the values specified by 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 option is specified: * Input characters found in the array specified by shall be deleted. * When the option is specified with all characters except those specified by shall be deleted. The contents of are ignored, unless the option is also specified. * When the option is specified with all values except those specified by shall be deleted. The contents of shall be ignored, unless the option is also specified. * The same string cannot be used for both the and the option; when both options are specified, both (used for deletion) and (used for squeezing) shall be required. When the 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 or character pairs, as appropriate. An empty string used for or produces undefined results. The following exit values shall be returned: 0 All input was processed successfully. >0 An error occurred. ‐6‐ Default. If necessary, and 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 is shorter than a difference results between historical System V and BSD systems. A BSD system pads with the last character found in Thus, it is possible to do the following: tr 0123456789 d which would translate all digits to the letter 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 are not regular expressions. Unlike some historical implementations, this definition of the utility correctly processes NUL characters in its input stream. NUL characters can be stripped by using: tr −d ’\000’ 1. The following example creates a list of all words in one per line in 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 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 in which are stripped of diacritical marks and written to tr "[=e=]" "[e*]" <file1 >file2 In some early proposals, an explicit option 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 in a later proposal does not remove the requirement that correctly process NUL characters in its input stream. NUL characters can be ‐7‐ stripped by using ’\000’. Historical implementations of differ widely in syntax and behavior. For example, the BSD version has not needed the bracket characters for the repetition sequence. The 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 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 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 does employ some syntactical elements from REs, the aim of 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 [:and [=conventions are shown with double brackets, as in RE syntax. However, does not implement RE principles; it just borrows part of the syntax. Consequently, [:and [=should be regarded as syntactical elements on a par with [which is not an RE bracket expression. The standard developers will consider changes to 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 representing the three characters and have to be rewritten as The ISO POSIX‐2:1993 standard had a option that behaved similarly to the option, but did not supply functionality equivalent to the option specified in POSIX.1‐2008. This ‐8‐ meant that historical practice of being able to specify (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 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. None. The Base Definitions volume of POSIX.1‐2008, 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 .