a2p
Awk to Perl translator
Synopsis
a2p
[options] [filename]
add an example, a script, a trick and tips
examples
source
.SUFFIXES: .c $(OBJ_EXT)
REALPERL = ../perl
CCCMD =
`sh $(shellflags) cflags
$@`
public =
a2p s2p find2perl
private =
private =
manpages =
a2p.man s2p.man
util =
sh = Makefile.SH
cflags.SH
shextract =
Makefile cflags
pl = find2perl.PL
s2p.PL
source
TRNL =
'\n'
.SUFFIXES: .c $(OBJ_EXT)
REALPERL = ../perl
CCCMD =
`sh $(shellflags) cflags
$@`
public =
a2p s2p find2perl
public = a2p s2p
find2perl
private =
manpages =
a2p.man s2p.man
util =
sh = Makefile.SH
cflags.SH
shextract =
Makefile cflags
source
timidity "$out"
}
function a2p {
if [ $# -eq 0 ]; then
echo 'usage a2p
<tune ref> <abc file>'
return 1
fi
abcm2ps -l -n -x "$file" -e $1 -O "$out"
fi
evince "$out"
}
function a2pm {
a2p $@; a2m $@
}
function a2mp {
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:
•
Old awk always has a line loop,
even if there are no line actions, whereas new awk does
not.
•
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,
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.
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.
diagnostics
environment
A2p uses no environment variables.
files
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.
see also
perl The perl compiler/interpreter
s2p sed to perl translator
author
Larry Wall
<larry[:at:]wall[:dot:]org>