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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 |
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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.1‐2017, 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.
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.1‐2017, 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.
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.1‐2017, 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.
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.1‐2017,
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'
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.
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.1‐2017, 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 1003.1-2017, 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)
Pages that refer to this page: dd(1p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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