2 ''' $RCSfile: a2p.man,v $$Revision: 4.1 $$Date: 92/08/07 18:29:10 $
23 ''' Set up \*(-- to give an unbreakable dash;
24 ''' string Tr holds user defined translation string.
25 ''' Bell System Logo is used as a dummy character.
30 .if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
31 .if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
47 a2p - Awk to Perl translator
49 .B a2p [options] filename
52 takes an awk script specified on the command line (or from standard input)
53 and produces a comparable
55 script on the standard output.
63 tells a2p that this awk script is always invoked with this -F switch.
66 specifies the names of the input fields if input does not have to be split into
68 If you were translating an awk script that processes the password file, you
71 a2p -7 -nlogin.password.uid.gid.gcos.shell.home
73 Any delimiter can be used to separate the field names.
76 causes a2p to assume that input will always have that many fields.
78 A2p cannot do as good a job translating as a human would, but it usually
80 There are some areas where you may want to examine the perl script produced
82 Here are some of them, in no particular order.
84 There is an awk idiom of putting int() around a string expression to force
85 numeric interpretation, even though the argument is always integer anyway.
86 This is generally unneeded in perl, but a2p can't tell if the argument
87 is always going to be integer, so it leaves it in.
88 You may wish to remove it.
90 Perl differentiates numeric comparison from string comparison.
91 Awk has one operator for both that decides at run time which comparison
93 A2p does not try to do a complete job of awk emulation at this point.
94 Instead it guesses which one you want.
95 It's almost always right, but it can be spoofed.
96 All such guesses are marked with the comment \*(L"#???\*(R".
97 You should go through and check them.
98 You might want to run at least once with the \-w switch to perl, which
99 will warn you if you use == where you should have used eq.
101 Perl does not attempt to emulate the behavior of awk in which nonexistent
102 array elements spring into existence simply by being referenced.
103 If somehow you are relying on this mechanism to create null entries for
104 a subsequent for...in, they won't be there in perl.
106 If a2p makes a split line that assigns to a list of variables that looks
107 like (Fld1, Fld2, Fld3...) you may want
108 to rerun a2p using the \-n option mentioned above.
109 This will let you name the fields throughout the script.
110 If it splits to an array instead, the script is probably referring to the number
113 The exit statement in awk doesn't necessarily exit; it goes to the END
114 block if there is one.
115 Awk scripts that do contortions within the END block to bypass the block under
116 such circumstances can be simplified by removing the conditional
117 in the END block and just exiting directly from the perl script.
119 Perl has two kinds of array, numerically-indexed and associative.
120 Awk arrays are usually translated to associative arrays, but if you happen
121 to know that the index is always going to be numeric you could change
123 Iteration over an associative array is done using the keys() function, but
124 iteration over a numeric array is NOT.
125 You might need to modify any loop that is iterating over the array in question.
127 Awk starts by assuming OFMT has the value %.6g.
128 Perl starts by assuming its equivalent, $#, to have the value %.20g.
129 You'll want to set $# explicitly if you use the default value of OFMT.
131 Near the top of the line loop will be the split operation that is implicit in
133 There are times when you can move this down past some conditionals that
134 test the entire record so that the split is not done as often.
136 For aesthetic reasons you may wish to change the array base $[ from 1 back
137 to perl's default of 0, but remember to change all array subscripts AND
138 all substr() and index() operations to match.
140 Cute comments that say "# Here is a workaround because awk is dumb" are passed
143 Awk scripts are often embedded in a shell script that pipes stuff into and
145 Often the shell script wrapper can be incorporated into the perl script, since
146 perl can start up pipes into and out of itself, and can do other things that
147 awk can't do by itself.
149 Scripts that refer to the special variables RSTART and RLENGTH can often
150 be simplified by referring to the variables $`, $& and $', as long as they
151 are within the scope of the pattern match that sets them.
153 The produced perl script may have subroutines defined to deal with awk's
154 semantics regarding getline and print.
155 Since a2p usually picks correctness over efficiency.
156 it is almost always possible to rewrite such code to be more efficient by
157 discarding the semantic sugar.
159 For efficiency, you may wish to remove the keyword from any return statement
160 that is the last statement executed in a subroutine.
161 A2p catches the most common case, but doesn't analyze embedded blocks for
164 ARGV[0] translates to $ARGV0, but ARGV[n] translates to $ARGV[$n].
165 A loop that tries to iterate over ARGV[0] won't find it.
167 A2p uses no environment variables.
169 Larry Wall <lwall@jpl-devvax.Jpl.Nasa.Gov>
172 perl The perl compiler/interpreter
174 s2p sed to perl translator
177 It would be possible to emulate awk's behavior in selecting string versus
178 numeric operations at run time by inspection of the operands, but it would
179 be gross and inefficient.
180 Besides, a2p almost always guesses right.
182 Storage for the awk syntax tree is currently static, and can run out.
https://perl5.git.perl.org / perl5.git / blob