diff options
Diffstat (limited to 'doc/gawktexi.in')
| -rw-r--r-- | doc/gawktexi.in | 42 |
1 files changed, 14 insertions, 28 deletions
diff --git a/doc/gawktexi.in b/doc/gawktexi.in index 0ec97419..f7fca2e7 100644 --- a/doc/gawktexi.in +++ b/doc/gawktexi.in @@ -13758,6 +13758,7 @@ or with Boolean operators (indeed, they cannot be used with any operators). An @command{awk} program may have multiple @code{BEGIN} and/or @code{END} rules. They are executed in the order in which they appear: all the @code{BEGIN} rules at startup and all the @code{END} rules at termination. + @code{BEGIN} and @code{END} rules may be intermixed with other rules. This feature was added in the 1987 version of @command{awk} and is included in the POSIX standard. @@ -13786,7 +13787,7 @@ run.@footnote{The original version of @command{awk} kept reading and ignoring input until the end of the file was seen.} However, if an @code{END} rule exists, then the input is read, even if there are no other rules in the program. This is necessary in case the @code{END} -rule checks the @code{FNR} and @code{NR} variables. +rule checks the @code{FNR} and @code{NR} variables, or the fields. @node I/O And BEGIN/END @subsubsection Input/Output from @code{BEGIN} and @code{END} Rules @@ -13814,6 +13815,7 @@ Traditionally, due largely to implementation issues, @code{$0} and @code{NF} were @emph{undefined} inside an @code{END} rule. The POSIX standard specifies that @code{NF} is available in an @code{END} rule. It contains the number of fields from the last input record. +@c FIXME: Update this if POSIX is ever fixed. Most probably due to an oversight, the standard does not say that @code{$0} is also preserved, although logically one would think that it should be. In fact, all of BWK @command{awk}, @command{mawk}, and @command{gawk} @@ -13825,7 +13827,7 @@ The third point follows from the first two. The meaning of @samp{print} inside a @code{BEGIN} or @code{END} rule is the same as always: @samp{print $0}. If @code{$0} is the null string, then this prints an empty record. Many longtime @command{awk} programmers use an unadorned -@samp{print} in @code{BEGIN} and @code{END} rules, to mean @samp{@w{print ""}}, +@samp{print} in @code{BEGIN} and @code{END} rules to mean @samp{@w{print ""}}, relying on @code{$0} being null. Although one might generally get away with this in @code{BEGIN} rules, it is a very bad idea in @code{END} rules, at least in @command{gawk}. It is also poor style, because if an empty @@ -13869,13 +13871,20 @@ As with the @code{BEGIN} and @code{END} rules @ifdocbook (see the previous @value{SECTION}), @end ifdocbook -all @code{BEGINFILE} rules in a program are merged, in the order they are -read by @command{gawk}, and all @code{ENDFILE} rules are merged as well. +@code{BEGINFILE} rules in a program are exectured in the order they are +read by @command{gawk}, and all @code{ENDFILE} rules are also executed in +the order they are read, as well. -The body of the @code{BEGINFILE} rules is executed just before +The bodies of the @code{BEGINFILE} rules execute just before @command{gawk} reads the first record from a file. @code{FILENAME} is set to the name of the current file, and @code{FNR} is set to zero. +Prior to @value{PVERSION} 5.1.1 of @command{gawk}, as an accident of the +implementation, @code{$0} and the fields retained any previous values +they had in @code{BEGINFILE} rules. Starting with @value{PVERSION} +5.1.1, @code{$0} and the fields are cleared, since no record has been +read yet from the file that is about to be processed. + The @code{BEGINFILE} rule provides you the opportunity to accomplish two tasks that would otherwise be difficult or impossible to perform: @@ -13930,28 +13939,6 @@ forms of @code{getline} are allowed. In most other @command{awk} implementations, or if @command{gawk} is in compatibility mode (@pxref{Options}), they are not special. -@c FIXME: For 4.2 maybe deal with this? -@ignore -Date: Tue, 17 May 2011 02:06:10 PDT -From: rankin@pactechdata.com (Pat Rankin) -Message-Id: <110517015127.20240f4a@pactechdata.com> -Subject: BEGINFILE -To: arnold@skeeve.com - - The documentation for BEGINFILE states that FNR is 0, which seems -pretty obvious. It doesn't mention what the value of $0 is, and that's -not obvious. I think setting it to null before starting the BEGINFILE -action would be preferable to leaving whatever was there in the last -record of the previous file. - - ENDFILE can retain the last record in $0. I guess it has to if -the END rule's actions see that value too. But the beginning of a new -file doesn't just mean that the old one has been closed; the old file -is being superseded, so leaving the old data around feels wrong to me. -[If the user wants to keep it on hand, he or she can use an ENDFILE -rule to grab it before moving on to the next file.] -@end ignore - @node Empty @subsection The Empty Pattern @@ -30984,7 +30971,6 @@ commands in a program. This can be very enlightening, as the following partial dump of Davide Brini's obfuscated code (@pxref{Signature Program}) demonstrates: -@c FIXME: This will need updating if num-handler branch is ever merged in. @smallexample @group gawk> @kbd{dump} |