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Diffstat (limited to 'doc/gawk.texi')
| -rw-r--r-- | doc/gawk.texi | 42 |
1 files changed, 31 insertions, 11 deletions
diff --git a/doc/gawk.texi b/doc/gawk.texi index a4b61895..90f6dcfc 100644 --- a/doc/gawk.texi +++ b/doc/gawk.texi @@ -12577,19 +12577,19 @@ One special place where @code{/foo/} is @emph{not} an abbreviation for where this is discussed in more detail. @node POSIX String Comparison -@subsubsection String Comparison with POSIX Rules +@subsubsection String Comparison Based on Locale Collating Order -The POSIX standard says that string comparison is performed based -on the locale's @dfn{collating order}. This is the order in which -characters sort, as defined by the locale (for more discussion, -@pxref{Locales}). This order is usually very different -from the results obtained when doing straight character-by-character -comparison.@footnote{Technically, string comparison is supposed -to behave the same way as if the strings were compared with the C -@code{strcoll()} function.} +The POSIX standard used to say that all string comparisons are +performed based on the locale's @dfn{collating order}. This +is the order in which characters sort, as defined by the locale +(for more discussion, @pxref{Locales}). This order is usually very +different from the results obtained when doing straight byte-by-byte +comparison.@footnote{Technically, string comparison is supposed to behave +the same way as if the strings were compared with the C @code{strcoll()} +function.} Because this behavior differs considerably from existing practice, -@command{gawk} only implements it when in POSIX mode (@pxref{Options}). +@command{gawk} only implemented it when in POSIX mode (@pxref{Options}). Here is an example to illustrate the difference, in an @code{en_US.UTF-8} locale: @@ -12602,6 +12602,26 @@ $ @kbd{gawk --posix 'BEGIN @{ printf("ABC < abc = %s\n",} @print{} ABC < abc = FALSE @end example +Fortunately, as of August 2016, comparison based on locale +collating order is no longer required for the @code{==} and @code{!=} +operators.@footnote{See @uref{http://austingroupbugs.net/view.php?id=1070, +the Austin Group website}.} However, comparison based on locales is still +required for @code{<}, @code{<=}, @code{>}, and @code{>=}. POSIX thus +recommends as follows: + +@quotation +Since the @code{==} operator checks whether strings are identical, +not whether they collate equally, applications needing to check whether +strings collate equally can use: + +@example +a <= b && a >= b +@end example +@end quotation + +As of @value{PVERSION} 4.2, @command{gawk} continues to use locale +collating order for @code{<}, @code{<=}, @code{>}, and @code{>=} only +in POSIX mode. @node Boolean Ops @subsection Boolean Expressions @@ -37385,7 +37405,7 @@ and @uref{http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xbd_chap09.html#tag_21_09_03_05, its rationale}.} By using this lovely technical term, the standard gives license -to implementors to implement ranges in whatever way they choose. +to implementers to implement ranges in whatever way they choose. The @command{gawk} maintainer chose to apply the pre-POSIX meaning both with the default regexp matching and when @option{--traditional} or @option{--posix} are used. |