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Man Page for A2PNAME
a2p - Awk to Perl translator
SYNOPSIS
a2p [options] filename
DESCRIPTION
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
Options include:
-D<number>
sets debugging flags.
-F<character>
tells a2p that this awk script is always invoked with
this -F switch.
-n<fieldlist>
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.
-<number>
causes a2p to assume that input will always have that
many fields.
Considerations
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.
Perl differentiates numeric comparison from string compar-
ison. 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 vari-
ables 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 refer-
ring 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 asso-
ciative. Awk arrays are usually translated to associative
arrays, but if you happen to know that the index is always
going to be numeric you could change the {...} to [...].
Iteration over an associative array is done using the
keys() function, but iteration over a numeric array is
NOT. You might need to modify any loop that is iterating
over the array in question.
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, 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 vari-
ables $`, $& 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
A2p uses no environment variables.
AUTHOR
Larry Wall <lwall@jpl-devvax.Jpl.Nasa.Gov>
FILESSEE ALSO
perl The perl compiler/interpreter
s2p sed to perl translator
DIAGNOSTICSBUGS
It would be possible to emulate awk's behavior in select-
ing string versus numeric operations at run time by
inspection of the operands, but it would be gross and
inefficient. Besides, a2p almost always guesses right.
Storage for the awk syntax tree is currently static, and
can run out.
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