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Diffstat (limited to 'doc/gawk.texi')
| -rw-r--r-- | doc/gawk.texi | 62 |
1 files changed, 39 insertions, 23 deletions
diff --git a/doc/gawk.texi b/doc/gawk.texi index 9519060e..d9c20831 100644 --- a/doc/gawk.texi +++ b/doc/gawk.texi @@ -12409,44 +12409,46 @@ function body reads the next record and starts processing it with the first rule in the program. @node Nextfile Statement -@subsection Using @command{gawk}'s @code{nextfile} Statement +@subsection The @code{nextfile} Statement @cindex @code{nextfile} statement @cindex differences in @command{awk} and @command{gawk}, @code{next}/@code{nextfile} statements @cindex common extensions, @code{nextfile} statement @cindex extensions, common@comma{} @code{nextfile} statement -@command{gawk} provides the @code{nextfile} statement, -which is similar to the @code{next} statement. @value{COMMONEXT} +The @code{nextfile} statement +is similar to the @code{next} statement. However, instead of abandoning processing of the current record, the -@code{nextfile} statement instructs @command{gawk} to stop processing the +@code{nextfile} statement instructs @command{awk} to stop processing the current @value{DF}. -The @code{nextfile} statement is a @command{gawk} extension. -In most other @command{awk} implementations, -or if @command{gawk} is in compatibility mode -(@pxref{Options}), -@code{nextfile} is not special. - Upon execution of the @code{nextfile} statement, -any @code{ENDFILE} rules are executed except in the case as -mentioned below, @code{FILENAME} is +@code{FILENAME} is updated to the name of the next @value{DF} listed on the command line, -@code{FNR} is reset to one, @code{ARGIND} is incremented, -any @code{BEGINFILE} rules are executed, and processing +@code{FNR} is reset to one, +and processing starts over with the first rule in the program. -(@code{ARGIND} hasn't been introduced yet. @xref{Built-in Variables}.) If the @code{nextfile} statement causes the end of the input to be reached, then the code in any @code{END} rules is executed. An exception to this is -when the @code{nextfile} is invoked during execution of any statement in an +when @code{nextfile} is invoked during execution of any statement in an @code{END} rule; In this case, it causes the program to stop immediately. @xref{BEGIN/END}. The @code{nextfile} statement is useful when there are many @value{DF}s to process but it isn't necessary to process every record in every file. -Normally, in order to move on to the next @value{DF}, a program -has to continue scanning the unwanted records. The @code{nextfile} +Without @code{nextfile}, +in order to move on to the next @value{DF}, a program +would have to continue scanning the unwanted records. The @code{nextfile} statement accomplishes this much more efficiently. -In addition, @code{nextfile} is useful inside a @code{BEGINFILE} +In @command{gawk}, execution of @code{nextfile} causes additional things +to happen: +any @code{ENDFILE} rules are executed except in the case as +mentioned below, +@code{ARGIND} is incremented, +and +any @code{BEGINFILE} rules are executed +(@code{ARGIND} hasn't been introduced yet. @xref{Built-in Variables}.) + +With @command{gawk}, @code{nextfile} is useful inside a @code{BEGINFILE} rule to skip over a file that would otherwise cause @command{gawk} to exit with a fatal error. In this case, @code{ENDFILE} rules are not executed. @xref{BEGINFILE/ENDFILE}. @@ -12457,6 +12459,13 @@ reserved for closing files, pipes, and coprocesses that are opened with redirections. It is not related to the main processing that @command{awk} does with the files listed in @code{ARGV}. +@quotation NOTE +For many years, @code{nextfile} was a +@command{gawk} extension. As of September, 2012, it was accepted for +inclusion into the POSIX standard. +See @uref{http://austingroupbugs.net/view.php?id=607, the Austin Group website}. +@end quotation + @cindex functions, user-defined, @code{next}/@code{nextfile} statements and @cindex @code{nextfile} statement, user-defined functions and The current version of the Brian Kernighan's @command{awk} (@pxref{Other @@ -13951,21 +13960,28 @@ is not in the array is deleted. @cindex deleting entire arrays @cindex differences in @command{awk} and @command{gawk}, array elements, deleting All the elements of an array may be deleted with a single statement -@value{COMMONEXT} by leaving off the subscript in the @code{delete} statement, as follows: + @example delete @var{array} @end example -This ability is a @command{gawk} extension; it is not available in -compatibility mode (@pxref{Options}). - Using this version of the @code{delete} statement is about three times more efficient than the equivalent loop that deletes each element one at a time. +@quotation NOTE +For many years, +using @code{delete} without a subscript was a @command{gawk} extension. +As of September, 2012, it was accepted for +inclusion into the POSIX standard. See @uref{http://austingroupbugs.net/view.php?id=544, +the Austin Group website}. This form of the @code{delete} statement is also supported +by Brian Kernighan's @command{awk} and @command{mawk}, as well as +by a number of other implementations (@pxref{Other Versions}). +@end quotation + @cindex portability, deleting array elements @cindex Brennan, Michael The following statement provides a portable but nonobvious way to clear |