*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->IRIX man pages -> a2p (1)              


A2P(1)									A2P(1)

NAME    [Toc]    [Back]

     a2p - Awk to Perl translator

SYNOPSIS    [Toc]    [Back]

     a2p [options] filename

DESCRIPTION    [Toc]    [Back]

     A2p takes an awk script specified on the command line (or from standard
     input) and	produces a comparable perl script on the standard output.

     Options    [Toc]    [Back]

     Options include:

	  sets debugging flags.

	  tells	a2p that this awk script is always invoked with	this -F

	  specifies the	names of the input fields if input does	not have to be
	  split	into an	array.	If you were translating	an awk script that
	  processes the	password file, you might say:

		  a2p -7 -nlogin.password.uid.gid.gcos.shell.home

	  Any delimiter	can be used to separate	the field names.

	  causes a2p to	assume that input will always have that	many fields.

     -o	  tells	a2p to use old awk behavior.  For now, the only	difference is
	  that old awk always has a line loop, even if there are no line
	  actions, whereas new awk does	not.


     A2p cannot	do as good a job translating as	a human	would, but it usually
     does pretty well.	There are some areas where you may want	to examine the
     perl script produced and tweak it some.  Here are some of them, in	no
     particular	order.

     There is an awk idiom of putting int() around a string expression to
     force numeric interpretation, even	though the argument is always integer
     anyway.  This is generally	unneeded in perl, but a2p can't	tell if	the
     argument is always	going to be integer, so	it leaves it in.  You may wish
     to	remove it.

									Page 1

A2P(1)									A2P(1)

     Perl differentiates numeric comparison from string	comparison.  Awk has
     one operator for both that	decides	at run time which comparison to	do.
     A2p does not try to do a complete job of awk emulation at this point.
     Instead it	guesses	which one you want.  It's almost always	right, but it
     can be spoofed.  All such guesses are marked with the comment "#???".
     You should	go through and check them.  You	might want to run at least
     once with the -w switch to	perl, which will warn you if you use ==	where
     you should	have used eq.

     Perl does not attempt to emulate the behavior of awk in which nonexistent
     array elements spring into	existence simply by being referenced.  If
     somehow you are relying on	this mechanism to create null entries for a
     subsequent	for...in, they won't be	there in perl.

     If	a2p makes a split line that assigns to a list of variables that	looks
     like (Fld1, Fld2, Fld3...)	you may	want to	rerun a2p using	the -n option
     mentioned above.  This will let you name the fields throughout the
     script.  If it splits to an array instead,	the script is probably
     referring to the number of	fields somewhere.

     The exit statement	in awk doesn't necessarily exit; it goes to the	END
     block if there is one.  Awk scripts that do contortions within the	END
     block to bypass the block under such circumstances	can be simplified by
     removing the conditional in the END block and just	exiting	directly from
     the perl script.

     Perl has two kinds	of array, numerically-indexed and associative.	Perl
     associative arrays	are called "hashes".  Awk arrays are usually
     translated	to hashes, but if you happen to	know that the index is always
     going to be numeric you could change the {...} to [...].  Iteration over
     a hash is done using the keys() function, but iteration over an array is
     NOT.  You might need to modify any	loop that iterates over	such an	array.

     Awk starts	by assuming OFMT has the value %.6g.  Perl starts by assuming
     its equivalent, $#, to have the value %.20g.  You'll want to set $#
     explicitly	if you use the default value of	OFMT.

     Near the top of the line loop will	be the split operation that is
     implicit in the awk script.  There	are times when you can move this down
     past some conditionals that test the entire record	so that	the split is
     not done as often.

     For aesthetic reasons you may wish	to change the array base $[ from 1
     back to perl's default of 0, but remember to change all array subscripts
     AND all substr() and index() operations to	match.

     Cute comments that	say "# Here is a workaround because awk	is dumb" are
     passed through unmodified.

     Awk scripts are often embedded in a shell script that pipes stuff into
     and out of	awk.  Often the	shell script wrapper can be incorporated into
     the perl script, since perl can start up pipes into and out of itself,

									Page 2

A2P(1)									A2P(1)

     and can do	other things that awk can't do by itself.

     Scripts that refer	to the special variables RSTART	and RLENGTH can	often
     be	simplified by referring	to the variables $`, $&	and $',	as long	as
     they are within the scope of the pattern match that sets them.

     The produced perl script may have subroutines defined to deal with	awk's
     semantics regarding getline and print.  Since a2p usually picks
     correctness over efficiency.  it is almost	always possible	to rewrite
     such code to be more efficient by discarding the semantic sugar.

     For efficiency, you may wish to remove the	keyword	from any return
     statement that is the last	statement executed in a	subroutine.  A2p
     catches the most common case, but doesn't analyze embedded	blocks for
     subtler cases.

     ARGV[0] translates	to $ARGV0, but ARGV[n] translates to $ARGV[$n].	 A
     loop that tries to	iterate	over ARGV[0] won't find	it.

ENVIRONMENT    [Toc]    [Back]

     A2p uses no environment variables.

AUTHOR    [Toc]    [Back]

     Larry Wall	<larry@wall.org>

FILES    [Toc]    [Back]

      perl   The perl compiler/interpreter

      s2p    sed to perl translator

DIAGNOSTICS    [Toc]    [Back]

     It	would be possible to emulate awk's behavior in selecting string	versus
     numeric operations	at run time by inspection of the operands, but it
     would be gross and	inefficient.  Besides, a2p almost always guesses

     Storage for the awk syntax	tree is	currently static, and can run out.

									Page 3

A2P(1)									A2P(1)

									PPPPaaaaggggeeee 4444
[ Back ]
 Similar pages
Name OS Title
s2p Linux Sed to Perl translator
s2p IRIX Sed to Perl translator
perlcompile OpenBSD Introduction to the Perl Compiler-Translator
perljp OpenBSD AEuEU,i Perl Y~YxYE `A^a`I`A Perl xIAx3|xOxex|x3x1/2! Perl 5.8.0 xexeicUni- _ codeYuYYi1/4YEx~AcEyxE...
pppoe OpenBSD PPP Over Ethernet translator
textps IRIX Text to PostScript translator
pdf2ps Linux Ghostscript PDF to PostScript translator
faithd OpenBSD FAITH IPv6/v4 translator daemon
XmTranslateKey HP-UX The default keycode-to-keysym translator
XmTranslateKey IRIX The default keycode-to-keysym translator
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service