a2p
(1)
Name
a2p - Awk to Perl translator
Synopsis
a2p [options] [filename]
Description
Perl Programmers Reference Guide A2P(1)
NAME
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.
-o tells a2p to use old awk behavior. The only current
differences are:
o Old awk always has a line loop, even if there are
no line actions, whereas new awk does not.
o In old awk, sprintf is extremely greedy about its
arguments. For example, given the statement
print sprintf(some_args), extra_args;
old awk considers extra_args to be arguments to
"sprintf"; new awk considers them arguments to
"print".
"Considerations"
A2p cannot do as good a job translating as a human would,
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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
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.
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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 index variables
from being 1-based (awk style) to 0-based (Perl style). Be
sure to change all operations the variable is involved in 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
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-1]. A loop that tries to iterate over ARGV[0]
won't find it.
ENVIRONMENT
A2p uses no environment variables.
AUTHOR
Larry Wall <larry@wall.org>
FILES
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ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/perl-512 |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
SEE ALSO
perl The perl compiler/interpreter
s2p sed to perl translator
DIAGNOSTICS
BUGS
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 right.
Storage for the awk syntax tree is currently static, and can
run out.
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://www.cpan.org/src/5.0/perl-5.12.5.tar.bz2
Further information about this software can be found on the
open source community website at http://www.perl.org/.
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