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Add a lengthy discussion of why "tr a-z A-Z" and "tr A-Z a-z" are not the

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right way to perform case-conversion.
This commit is contained in:
Tim J. Robbins 2004-07-23 05:44:04 +00:00
parent 2a1c4385c3
commit 0b651019b4
1 changed files with 41 additions and 1 deletions
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42
usr.bin/tr/tr.1
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@ -35,7 +35,7 @@
.\" @(#)tr.1 8.1 (Berkeley) 6/6/93
.\" $FreeBSD$
.\"
.Dd July 9, 2004
.Dd July 23, 2004
.Dt TR 1
.Os
.Sh NAME
@ -169,6 +169,13 @@ as defined by the collation sequence.
If either or both of the range endpoints are octal sequences, it
represents the range of specific coded values between the
range endpoints, inclusive.
.Pp
.Bf Em
See the COMPATIBILITY section below for an important note regarding
differences in the way the current
implementation interprets range expressions differently from
previous implementations.
.Ef
.It [:class:]
Represents all characters belonging to the defined character class.
Class names are:
@ -274,6 +281,12 @@ Translate the contents of file1 to upper-case.
.Pp
.D1 Li "tr \*q[:lower:]\*q \*q[:upper:]\*q < file1"
.Pp
(This should be preferred over the traditional
.Ux
idiom of
.Ql "tr a-z A-Z" ,
since it works correctly in all locales.)
.Pp
Strip out non-printable characters from file1.
.Pp
.D1 Li "tr -cd \*q[:print:]\*q < file1"
@ -285,6 +298,33 @@ Remove diacritical marks from all accented variants of the letter
.Sh DIAGNOSTICS
.Ex -std
.Sh COMPATIBILITY
Previous
.Fx
implementations of
.Nm
did not order characters in range expressions according to the current
locale's collation order, making it possible to convert unaccented Latin
characters (esp. as found in English text) from upper to lower case using
the traditional
.Ux
idiom of
.Ql "tr A-Z a-z" .
Since
.Nm
now obeys the locale's collation order, this idiom may not produce
correct results when there is not a 1:1 mapping between lower and
upper case, or when the order of characters within the two cases differs.
As noted in the
.Sx EXAMPLES
section above, the character class expressions
.Ql "[:lower:]"
and
.Ql "[:upper:]"
should be used instead of explicit character ranges like
.Ql "a-z"
and
.Ql "A-Z" .
.Pp
System V has historically implemented character ranges using the syntax
``[c-c]'' instead of the ``c-c'' used by historic
.Bx