200 lines
6.6 KiB
Groff
200 lines
6.6 KiB
Groff
.rn '' }`
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''' $Header: /home/cvs/386BSD/ports/lang/perl/x2p/a2p.man,v 1.1.1.1 1993/08/23 21:30:10 nate Exp $
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'''
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''' $Log: a2p.man,v $
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.\" Revision 1.1.1.1 1993/08/23 21:30:10 nate
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.\" PERL!
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.\"
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''' Revision 4.0 91/03/20 01:57:11 lwall
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''' 4.0 baseline.
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'''
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''' Revision 3.0 89/10/18 15:34:22 lwall
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''' 3.0 baseline
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'''
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''' Revision 2.0.1.1 88/07/11 23:16:25 root
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''' patch2: changes related to 1985 awk
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'''
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''' Revision 2.0 88/06/05 00:15:36 root
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''' Baseline version 2.0.
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'''
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'''
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.de Sh
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.br
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.ne 5
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.PP
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\fB\\$1\fR
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.PP
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..
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.de Sp
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.if t .sp .5v
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.if n .sp
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..
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.de Ip
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.br
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.ie \\n.$>=3 .ne \\$3
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.el .ne 3
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.IP "\\$1" \\$2
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..
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'''
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''' Set up \*(-- to give an unbreakable dash;
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''' string Tr holds user defined translation string.
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''' Bell System Logo is used as a dummy character.
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'''
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.tr \(*W-|\(bv\*(Tr
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.ie n \{\
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.ds -- \(*W-
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.if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
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.if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
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.ds L" ""
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.ds R" ""
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.ds L' '
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.ds R' '
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'br\}
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.el\{\
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.ds -- \(em\|
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.tr \*(Tr
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.ds L" ``
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.ds R" ''
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.ds L' `
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.ds R' '
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'br\}
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.TH A2P 1 LOCAL
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.SH NAME
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a2p - Awk to Perl translator
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.SH SYNOPSIS
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.B a2p [options] filename
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.SH DESCRIPTION
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.I A2p
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takes an awk script specified on the command line (or from standard input)
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and produces a comparable
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.I perl
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script on the standard output.
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.Sh "Options"
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Options include:
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.TP 5
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.B \-D<number>
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sets debugging flags.
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.TP 5
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.B \-F<character>
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tells a2p that this awk script is always invoked with this -F switch.
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.TP 5
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.B \-n<fieldlist>
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specifies the names of the input fields if input does not have to be split into
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an array.
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If you were translating an awk script that processes the password file, you
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might say:
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.sp
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a2p -7 -nlogin.password.uid.gid.gcos.shell.home
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.sp
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Any delimiter can be used to separate the field names.
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.TP 5
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.B \-<number>
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causes a2p to assume that input will always have that many fields.
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.Sh "Considerations"
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A2p cannot do as good a job translating as a human would, but it usually
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does pretty well.
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There are some areas where you may want to examine the perl script produced
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and tweak it some.
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Here are some of them, in no particular order.
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.PP
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There is an awk idiom of putting int() around a string expression to force
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numeric interpretation, even though the argument is always integer anyway.
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This is generally unneeded in perl, but a2p can't tell if the argument
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is always going to be integer, so it leaves it in.
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You may wish to remove it.
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.PP
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Perl differentiates numeric comparison from string comparison.
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Awk has one operator for both that decides at run time which comparison
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to do.
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A2p does not try to do a complete job of awk emulation at this point.
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Instead it guesses which one you want.
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It's almost always right, but it can be spoofed.
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All such guesses are marked with the comment \*(L"#???\*(R".
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You should go through and check them.
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You might want to run at least once with the \-w switch to perl, which
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will warn you if you use == where you should have used eq.
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.PP
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Perl does not attempt to emulate the behavior of awk in which nonexistent
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array elements spring into existence simply by being referenced.
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If somehow you are relying on this mechanism to create null entries for
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a subsequent for...in, they won't be there in perl.
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.PP
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If a2p makes a split line that assigns to a list of variables that looks
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like (Fld1, Fld2, Fld3...) you may want
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to rerun a2p using the \-n option mentioned above.
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This will let you name the fields throughout the script.
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If it splits to an array instead, the script is probably referring to the number
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of fields somewhere.
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.PP
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The exit statement in awk doesn't necessarily exit; it goes to the END
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block if there is one.
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Awk scripts that do contortions within the END block to bypass the block under
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such circumstances can be simplified by removing the conditional
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in the END block and just exiting directly from the perl script.
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.PP
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Perl has two kinds of array, numerically-indexed and associative.
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Awk arrays are usually translated to associative arrays, but if you happen
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to know that the index is always going to be numeric you could change
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the {...} to [...].
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Iteration over an associative array is done using the keys() function, but
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iteration over a numeric array is NOT.
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You might need to modify any loop that is iterating over the array in question.
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.PP
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Awk starts by assuming OFMT has the value %.6g.
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Perl starts by assuming its equivalent, $#, to have the value %.20g.
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You'll want to set $# explicitly if you use the default value of OFMT.
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.PP
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Near the top of the line loop will be the split operation that is implicit in
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the awk script.
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There are times when you can move this down past some conditionals that
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test the entire record so that the split is not done as often.
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.PP
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For aesthetic reasons you may wish to change the array base $[ from 1 back
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to perl's default of 0, but remember to change all array subscripts AND
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all substr() and index() operations to match.
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.PP
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Cute comments that say "# Here is a workaround because awk is dumb" are passed
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through unmodified.
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.PP
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Awk scripts are often embedded in a shell script that pipes stuff into and
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out of awk.
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Often the shell script wrapper can be incorporated into the perl script, since
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perl can start up pipes into and out of itself, and can do other things that
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awk can't do by itself.
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.PP
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Scripts that refer to the special variables RSTART and RLENGTH can often
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be simplified by referring to the variables $`, $& and $', as long as they
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are within the scope of the pattern match that sets them.
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.PP
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The produced perl script may have subroutines defined to deal with awk's
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semantics regarding getline and print.
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Since a2p usually picks correctness over efficiency.
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it is almost always possible to rewrite such code to be more efficient by
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discarding the semantic sugar.
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.PP
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For efficiency, you may wish to remove the keyword from any return statement
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that is the last statement executed in a subroutine.
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A2p catches the most common case, but doesn't analyze embedded blocks for
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subtler cases.
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.PP
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ARGV[0] translates to $ARGV0, but ARGV[n] translates to $ARGV[$n].
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A loop that tries to iterate over ARGV[0] won't find it.
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.SH ENVIRONMENT
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A2p uses no environment variables.
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.SH AUTHOR
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Larry Wall <lwall@jpl-devvax.Jpl.Nasa.Gov>
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.SH FILES
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.SH SEE ALSO
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perl The perl compiler/interpreter
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.br
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s2p sed to perl translator
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.SH DIAGNOSTICS
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.SH BUGS
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It would be possible to emulate awk's behavior in selecting string versus
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numeric operations at run time by inspection of the operands, but it would
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be gross and inefficient.
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Besides, a2p almost always guesses right.
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.PP
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Storage for the awk syntax tree is currently static, and can run out.
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.rn }` ''
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