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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.

       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>


FILES


SEE ALSO

       perl The perl compiler/interpreter
       s2p  sed to perl translator


DIAGNOSTICS


BUGS

       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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