1=head1 NAME 2 3a2p - Awk to Perl translator 4 5=head1 SYNOPSIS 6 7B<a2p [options] filename> 8 9=head1 DESCRIPTION 10 11I<A2p> takes an awk script specified on the command line (or from 12standard input) and produces a comparable I<perl> script on the 13standard output. 14 15=head2 Options 16 17Options include: 18 19=over 5 20 21=item B<-DE<lt>numberE<gt>> 22 23sets debugging flags. 24 25=item B<-FE<lt>characterE<gt>> 26 27tells a2p that this awk script is always invoked with this B<-F> 28switch. 29 30=item B<-nE<lt>fieldlistE<gt>> 31 32specifies the names of the input fields if input does not have to be 33split into an array. If you were translating an awk script that 34processes the password file, you might say: 35 36 a2p -7 -nlogin.password.uid.gid.gcos.shell.home 37 38Any delimiter can be used to separate the field names. 39 40=item B<-E<lt>numberE<gt>> 41 42causes a2p to assume that input will always have that many fields. 43 44=item B<-o> 45 46tells a2p to use old awk behavior. The only current differences are: 47 48=over 5 49 50=item * 51 52Old awk always has a line loop, even if there are no line 53actions, whereas new awk does not. 54 55=item * 56 57In old awk, sprintf is extremely greedy about its arguments. 58For example, given the statement 59 60 print sprintf(some_args), extra_args; 61 62old awk considers I<extra_args> to be arguments to C<sprintf>; new awk 63considers them arguments to C<print>. 64 65=back 66 67=back 68 69=head2 "Considerations" 70 71A2p cannot do as good a job translating as a human would, but it 72usually does pretty well. There are some areas where you may want to 73examine the perl script produced and tweak it some. Here are some of 74them, in no particular order. 75 76There is an awk idiom of putting int() around a string expression to 77force numeric interpretation, even though the argument is always 78integer anyway. This is generally unneeded in perl, but a2p can't 79tell if the argument is always going to be integer, so it leaves it 80in. You may wish to remove it. 81 82Perl differentiates numeric comparison from string comparison. Awk 83has one operator for both that decides at run time which comparison to 84do. A2p does not try to do a complete job of awk emulation at this 85point. Instead it guesses which one you want. It's almost always 86right, but it can be spoofed. All such guesses are marked with the 87comment "C<#???>". You should go through and check them. You might 88want to run at least once with the B<-w> switch to perl, which will 89warn you if you use == where you should have used eq. 90 91Perl does not attempt to emulate the behavior of awk in which 92nonexistent array elements spring into existence simply by being 93referenced. If somehow you are relying on this mechanism to create 94null entries for a subsequent for...in, they won't be there in perl. 95 96If a2p makes a split line that assigns to a list of variables that 97looks like (Fld1, Fld2, Fld3...) you may want to rerun a2p using the 98B<-n> option mentioned above. This will let you name the fields 99throughout the script. If it splits to an array instead, the script 100is probably referring to the number of fields somewhere. 101 102The exit statement in awk doesn't necessarily exit; it goes to the END 103block if there is one. Awk scripts that do contortions within the END 104block to bypass the block under such circumstances can be simplified 105by removing the conditional in the END block and just exiting directly 106from the perl script. 107 108Perl has two kinds of array, numerically-indexed and associative. 109Perl associative arrays are called "hashes". Awk arrays are usually 110translated to hashes, but if you happen to know that the index is 111always going to be numeric you could change the {...} to [...]. 112Iteration over a hash is done using the keys() function, but iteration 113over an array is NOT. You might need to modify any loop that iterates 114over such an array. 115 116Awk starts by assuming OFMT has the value %.6g. Perl starts by 117assuming its equivalent, $#, to have the value %.20g. You'll want to 118set $# explicitly if you use the default value of OFMT. 119 120Near the top of the line loop will be the split operation that is 121implicit in the awk script. There are times when you can move this 122down past some conditionals that test the entire record so that the 123split is not done as often. 124 125For aesthetic reasons you may wish to change the array base $[ from 1 126back to perl's default of 0, but remember to change all array 127subscripts AND all substr() and index() operations to match. 128 129Cute comments that say "# Here is a workaround because awk is dumb" 130are passed through unmodified. 131 132Awk scripts are often embedded in a shell script that pipes stuff into 133and out of awk. Often the shell script wrapper can be incorporated 134into the perl script, since perl can start up pipes into and out of 135itself, and can do other things that awk can't do by itself. 136 137Scripts that refer to the special variables RSTART and RLENGTH can 138often be simplified by referring to the variables $`, $& and $', as 139long as they are within the scope of the pattern match that sets them. 140 141The produced perl script may have subroutines defined to deal with 142awk's semantics regarding getline and print. Since a2p usually picks 143correctness over efficiency. it is almost always possible to rewrite 144such code to be more efficient by discarding the semantic sugar. 145 146For efficiency, you may wish to remove the keyword from any return 147statement that is the last statement executed in a subroutine. A2p 148catches the most common case, but doesn't analyze embedded blocks for 149subtler cases. 150 151ARGV[0] translates to $ARGV0, but ARGV[n] translates to $ARGV[$n]. A 152loop that tries to iterate over ARGV[0] won't find it. 153 154=head1 ENVIRONMENT 155 156A2p uses no environment variables. 157 158=head1 AUTHOR 159 160Larry Wall E<lt>F<larry@wall.org>E<gt> 161 162=head1 FILES 163 164=head1 SEE ALSO 165 166 perl The perl compiler/interpreter 167 168 s2p sed to perl translator 169 170=head1 DIAGNOSTICS 171 172=head1 BUGS 173 174It would be possible to emulate awk's behavior in selecting string 175versus numeric operations at run time by inspection of the operands, 176but it would be gross and inefficient. Besides, a2p almost always 177guesses right. 178 179Storage for the awk syntax tree is currently static, and can run out. 180