.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "TR" P 2003 POSIX
.\" tr 
.SH NAME
tr \- translate characters
.SH SYNOPSIS
.LP
\fBtr\fP \fB[\fP\fB-c | -C\fP\fB][\fP\fB-s]\fP \fIstring1 string2\fP\fB
.br
.sp
tr -s\fP \fB[\fP\fB-c | -C\fP\fB]\fP \fIstring1\fP\fB
.br
.sp
tr -d\fP \fB[\fP\fB-c | -C\fP\fB]\fP \fIstring1\fP\fB
.br
.sp
tr -ds\fP \fB[\fP\fB-c | -C\fP\fB]\fP \fIstring1 string2\fP\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fItr\fP utility shall copy the standard input to the standard
output with substitution or deletion of selected characters.
The options specified and the \fIstring1\fP and \fIstring2\fP operands
shall control translations that occur while copying
characters and single-character collating elements.
.SH OPTIONS
.LP
The \fItr\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following options shall be supported:
.TP 7
\fB-c\fP
Complement the set of values specified by \fIstring1\fP. See the EXTENDED
DESCRIPTION section.
.TP 7
\fB-C\fP
Complement the set of characters specified by \fIstring1\fP. See the
EXTENDED DESCRIPTION section.
.TP 7
\fB-d\fP
Delete all occurrences of input characters that are specified by \fIstring1\fP.
.TP 7
\fB-s\fP
Replace instances of repeated characters with a single character,
as described in the EXTENDED DESCRIPTION section.
.sp
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIstring1\fP,\ \fIstring2\fP
.sp
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.
.sp
.SH STDIN
.LP
The standard input can be any type of file.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fItr\fP:
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_COLLATE\fP
.sp
Determine the locale for the behavior of range expressions and equivalence
classes.
.TP 7
\fILC_CTYPE\fP
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.
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
The \fItr\fP output shall be identical to the input, with the exception
of the specified transformations.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
The operands \fIstring1\fP and \fIstring2\fP (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, \fItr\fP shall exclude, without a diagnostic,
those multi-character elements from the resulting array.
.TP 7
\fIcharacter\fP
Any character not described by one of the conventions below shall
represent itself.
.TP 7
\\\fIoctal\fP
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. If the size of a byte on the
system is greater than nine bits, the valid escape sequence used to
represent a byte is implementation-defined. Multi-byte
characters require multiple, concatenated escape sequences of this
type, including the leading \fB'\\'\fP for each byte.
.TP 7
\\\fIcharacter\fP
The backslash-escape sequences in the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
Table 5-1, Escape Sequences
and Associated Actions ( \fB'\\\\'\fP , \fB'\\a'\fP , \fB'\\b'\fP
, \fB'\\f'\fP , \fB'\\n'\fP , \fB'\\r'\fP ,
\fB'\\t'\fP , \fB'\\v'\fP ) shall be supported. The results of using
any other character, other than an octal digit, following
the backslash are unspecified.
.TP 7
\fIc\fP-\fIc\fP
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 \\\fIoctal\fP),
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. 
.LP
If either or both of the range endpoints are octal sequences of the
form \\\fIoctal\fP, this shall represent the range of
specific coded values between the two range endpoints, inclusive.
.TP 7
.B :\fIclass\fP:
Represents all characters belonging to the defined character class,
as defined by the current setting of the \fILC_CTYPE\fP
locale category. The following character class names shall be accepted
when specified in \fIstring1\fP: 
.TS C
center; l l l l l l.
\fBalnum\fP	\fBblank\fP	\fBdigit\fP	\fBlower\fP	\fBpunct\fP	\fBupper\fP
\fBalpha\fP	\fBcntrl\fP	\fBgraph\fP	\fBprint\fP	\fBspace\fP	\fBxdigit\fP
.TE
.LP
In addition, character class expressions of the form [: \fIname\fP:]
shall be recognized in those locales where the \fIname\fP
keyword has been given a \fBcharclass\fP definition in the \fILC_CTYPE\fP
category. 
.LP
When both the \fB-d\fP and \fB-s\fP options are specified, any of
the character class names shall be accepted in
\fIstring2\fP. Otherwise, only character class names \fBlower\fP or
\fBupper\fP are valid in \fIstring2\fP and then only if the
corresponding character class ( \fBupper\fP and \fBlower\fP, respectively)
is specified in the same relative position in
\fIstring1\fP. Such a specification shall be interpreted as a request
for case conversion. When [: \fIlower\fP:] appears in
\fIstring1\fP and [: \fIupper\fP:] appears in \fIstring2\fP, the arrays
shall contain the characters from the \fBtoupper\fP
mapping in the \fILC_CTYPE\fP category of the current locale. When
[: \fIupper\fP:] appears in \fIstring1\fP and [:
\fIlower\fP:] appears in \fIstring2\fP, the arrays shall contain the
characters from the \fBtolower\fP mapping in the
\fILC_CTYPE\fP category of the current locale. The first character
from each mapping pair shall be in the array for \fIstring1\fP
and the second character from each mapping pair shall be in the array
for \fIstring2\fP in the same relative position.
.LP
Except for case conversion, the characters specified by a character
class expression shall be placed in the array in an
unspecified order.
.LP
If the name specified for \fIclass\fP does not define a valid character
class in the current locale, the behavior is
undefined.
.TP 7
.B =\fIequiv\fP=
Represents all characters or collating elements belonging to the same
equivalence class as \fIequiv\fP, as defined by the
current setting of the \fILC_COLLATE\fP locale category. An equivalence
class expression shall be allowed only in \fIstring1\fP,
or in \fIstring2\fP when it is being used by the combined \fB-d\fP
and \fB-s\fP options. The characters belonging to the
equivalence class shall be placed in the array in an unspecified order.
.TP 7
.B \fIx\fP*\fIn\fP
Represents \fIn\fP repeated occurrences of the character \fIx\fP.
Because this expression is used to map multiple characters
to one, it is only valid when it occurs in \fIstring2\fP. If \fIn\fP
is omitted or is zero, it shall be interpreted as large
enough to extend the \fIstring2\fP-based sequence to the length of
the \fIstring1\fP-based sequence. If \fIn\fP has a leading
zero, it shall be interpreted as an octal value. Otherwise, it shall
be interpreted as a decimal value.
.sp
.LP
When the \fB-d\fP option is not specified:
.IP " *" 3
Each input character found in the array specified by \fIstring1\fP
shall be replaced by the character in the same relative
position in the array specified by \fIstring2\fP. When the array specified
by \fIstring2\fP is shorter that the one specified by
\fIstring1\fP, the results are unspecified.
.LP
.IP " *" 3
If the \fB-C\fP option is specified, the complements of the characters
specified by \fIstring1\fP (the set of all characters
in the current character set, as defined by the current setting of
\fILC_CTYPE ,\fP except for those actually specified in the
\fIstring1\fP operand) shall be placed in the array in ascending collation
sequence, as defined by the current setting of
\fILC_COLLATE .\fP
.LP
.IP " *" 3
If the \fB-c\fP option is specified, the complement of the values
specified by \fIstring1\fP shall be placed in the array in
ascending order by binary value.
.LP
.IP " *" 3
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.
.LP
.LP
When the \fB-d\fP option is specified:
.IP " *" 3
Input characters found in the array specified by \fIstring1\fP shall
be deleted.
.LP
.IP " *" 3
When the \fB-C\fP option is specified with \fB-d\fP, all characters
except those specified by \fIstring1\fP shall be deleted.
The contents of \fIstring2\fP are ignored, unless the \fB-s\fP option
is also specified.
.LP
.IP " *" 3
When the \fB-c\fP option is specified with \fB-d\fP, all values except
those specified by \fIstring1\fP shall be deleted. The
contents of \fIstring2\fP shall be ignored, unless the \fB-s\fP option
is also specified.
.LP
.IP " *" 3
The same string cannot be used for both the \fB-d\fP and the \fB-s\fP
option; when both options are specified, both
\fIstring1\fP (used for deletion) and \fIstring2\fP (used for squeezing)
shall be required.
.LP
.LP
When the \fB-s\fP 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:
.sp
.RS
.nf

\fBtr -s '[:space:]'
\fP
.fi
.RE
.LP
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:
.sp
.RS
.nf

\fBtr -s '[:upper:]' '[:lower:]'
\fP
.fi
.RE
.LP
the last operand's array shall contain only those characters defined
as the second characters in each of the \fBtoupper\fP or
\fBtolower\fP character pairs, as appropriate.
.LP
An empty string used for \fIstring1\fP or \fIstring2\fP produces undefined
results.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
All input was processed successfully.
.TP 7
>0
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
If necessary, \fIstring1\fP and \fIstring2\fP can be quoted to avoid
pattern matching by the shell.
.LP
If an ordinary digit (representing itself) is to follow an octal sequence,
the octal sequence must use the full three digits to
avoid ambiguity.
.LP
When \fIstring2\fP is shorter than \fIstring1\fP, a difference results
between historical System\ V and BSD systems. A BSD
system pads \fIstring2\fP with the last character found in \fIstring2\fP.
Thus, it is possible to do the following:
.sp
.RS
.nf

\fBtr 0123456789 d
\fP
.fi
.RE
.LP
which would translate all digits to the letter \fB'd'\fP . Since this
area is specifically unspecified in this volume of
IEEE\ Std\ 1003.1-2001, 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:
.sp
.RS
.nf

\fBtr 0123456789 '[d*]'
\fP
.fi
.RE
.LP
It should be noted that, despite similarities in appearance, the string
operands used by \fItr\fP are not regular
expressions.
.LP
Unlike some historical implementations, this definition of the \fItr\fP
utility correctly processes NUL characters in its input
stream. NUL characters can be stripped by using:
.sp
.RS
.nf

\fBtr -d '\\000'
\fP
.fi
.RE
.SH EXAMPLES
.IP " 1." 4
The following example creates a list of all words in \fBfile1\fP one
per line in \fBfile2\fP, where a word is taken to be a
maximal string of letters.
.sp
.RS
.nf

\fBtr -cs "[:alpha:]" "[\\n*]" <file1 >file2
\fP
.fi
.RE
.LP
.IP " 2." 4
The next example translates all lowercase characters in \fBfile1\fP
to uppercase and writes the results to standard output.
.sp
.RS
.nf

\fBtr "[:lower:]" "[:upper:]" <file1
\fP
.fi
.RE
.LP
.IP " 3." 4
This example uses an equivalence class to identify accented variants
of the base character \fB'e'\fP in \fBfile1\fP, which
are stripped of diacritical marks and written to \fBfile2\fP.
.sp
.RS
.nf

\fBtr "[=e=]" e <file1 >file2
\fP
.fi
.RE
.LP
.SH RATIONALE
.LP
In some early proposals, an explicit option \fB-n\fP 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 \fB-n\fP in a later proposal does not remove
the requirement that \fItr\fP correctly process NUL
characters in its input stream. NUL characters can be stripped by
using \fItr\fP \fB-d\fP '\\000'.
.LP
Historical implementations of \fItr\fP differ widely in syntax and
behavior. For example, the BSD version has not needed the
bracket characters for the repetition sequence. The \fItr\fP 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 \fIstring2\fP 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 \fItr\fP 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.
.LP
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.
.LP
An early proposal included support for multi-character collating elements.
It was pointed out that, while \fItr\fP does employ
some syntactical elements from REs, the aim of \fItr\fP is quite different;
ranges, for example, do not have a similar meaning
(``any of the chars in the range matches", \fIversus\fP "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.
.LP
In XPG3 the [: \fIclass\fP:] and [= \fIequiv\fP=] conventions are
shown with double brackets, as in RE syntax. However,
\fItr\fP does not implement RE principles; it just borrows part of
the syntax. Consequently, [: \fIclass\fP:] and [=
\fIequiv\fP=] should be regarded as syntactical elements on a par
with [ \fIx\fP* \fIn\fP], which is not an RE bracket
expression.
.LP
The standard developers will consider changes to \fItr\fP that allow
it to translate characters between different character
encodings, or they will consider providing a new utility to accomplish
this.
.LP
On historical System V systems, a range expression requires enclosing
square-brackets, such as:
.sp
.RS
.nf

\fBtr '[a-z]' '[A-Z]'
\fP
.fi
.RE
.LP
However, BSD-based systems did not require the brackets, and this
convention is used here to avoid breaking large numbers of BSD
scripts:
.sp
.RS
.nf

\fBtr a-z A-Z
\fP
.fi
.RE
.LP
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 \fB"a-z"\fP
representing the three characters \fB'a'\fP ,
\fB'-'\fP , and \fB'z'\fP have to be rewritten as \fB"az-"\fP .
.LP
The ISO\ POSIX-2:1993 standard had a \fB-c\fP option that behaved
similarly to the \fB-C\fP option, but did not supply
functionality equivalent to the \fB-c\fP option specified in IEEE\ Std\ 1003.1-2001.
This meant that historical practice
of being able to specify \fItr\fP \fB-d\fP\\200-\\377 (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.
.LP
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 \fItr\fP would not be able to tell
whether adjacent octal sequences were intending to specify multi-byte
characters or multiple single byte characters.
IEEE\ Std\ 1003.1-2001 specifies that octal sequences always refer
to single byte binary values.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIsed\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .