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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)
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 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.
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.
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.
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.
Default.
The tr 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 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.
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.
The following exit values shall be returned:
0 All input was processed successfully.
>0 An error occurred.
Default.
The following sections are informative.
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'
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
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.
None.
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
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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