a2p

awk to perl translator 

Command


SYNOPSIS

a2p [-Dnumber] [-Fcharacter] [-nfieldlist] [-number] [filename]


DESCRIPTION

a2p takes an awk script specified on the command line (or from standard input), produces a comparable perl script, and writes it to standard output.

Options

-Dnumber 

sets debugging flags.

-Fcharacter 

specifies that this awk script is always invoked with this -F option.

-nfieldlist 

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 

assumes that the input always has number fields.


NOTES

a2p cannot do as good a job translating as a human would, but it usually does reasonably well. There are some areas where you may want to examine the perl script produced and tweak it.

There is an awk idiom of putting int() around a string expression to force numeric interpretation, even though the argument is always an integer anyway. This is generally unneeded in perl, but a2p cannot tell that the argument is always going to be an 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 comparison you want. It's almost always right, but it can be spoofed. All such guesses are marked with the comment #??? so you can go through and check them. You might also want to run at least once with the -w option to perl, which warns 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. Do not rely on this mechanism to create null entries for a subsequent for...in; they will not 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 lets you name the fields throughout the script. If a2p splits to an array instead, the script is probably referring to the number of fields somewhere.

The exit statement in awk does not 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 can be simplified by removing the conditional in the END block and then exiting directly from the perl script.

perl has two kinds of arrays: numerically-indexed and associative. awk arrays are usually translated to associative arrays, but if you know that the index is always going to be numeric you could change the {...} to [...]. Iteration over an associative array uses the keys() function, but iteration over a numeric array does 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 must set $# explicitly if you use the default value of OFMT.

Near the top of the line loop is 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 performed 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 data 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 cannot accomplish.

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 embellishments.

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 does not 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] will not be able to do so.

It would be possible to emulate awk's behavior in selecting string versus numeric operations at run time by inspecting the operands, but it would be grossly inefficient: a2p almost always guesses correctly.

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


AUTHOR

The original version of a2p is Copyright (c) 1991 Larry Wall.


LICENSING

The file a2p.exe is subject to the Artistic License (see the $ROOTDIR/etc/perl/artistic file). No fee is charged as part of this package for this object. The source for a2p is available from MKS.


PORTABILITY

All UNIX systems. Windows 7. Windows Server 2008 R2. Windows 8. Windows Server 2012. Windows 10. Windows Server 2016.


AVAILABILITY

PTC MKS Toolkit for Power Users
PTC MKS Toolkit for System Administrators
PTC MKS Toolkit for Developers
PTC MKS Toolkit for Interoperability
PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Professional Developers 64-Bit Edition
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition
PTC Integrity


SEE ALSO

Commands:
awk, perl


PTC MKS Toolkit 10.1 Documentation Build 15.