1A2P(1) Perl Programmers Reference Guide A2P(1)
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6 a2p - Awk to Perl translator
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9 a2p [options] [filename]
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12 A2p takes an awk script specified on the command line (or from standard
13 input) and produces a comparable perl script on the standard output.
14 OPTIONS
16 Options include:
18 -D<number>
20 sets debugging flags.
21 -F<character>
23 tells a2p that this awk script is always invoked with this -F
24 switch.
25 -n<fieldlist>
27 specifies the names of the input fields if input does not have to
28 be split into an array. If you were translating an awk script
29 that processes the password file, you might say:
30 a2p -7 -nlogin.password.uid.gid.gcos.shell.home
32 Any delimiter can be used to separate the field names.
34 -<number>
36 causes a2p to assume that input will always have that many fields.
37 -o tells a2p to use old awk behavior. The only current differences
39 are:
40 * Old awk always has a line loop, even if there are no line
42 actions, whereas new awk does not.
43 * In old awk, sprintf is extremely greedy about its arguments.
45 For example, given the statement
46 print sprintf(some_args), extra_args;
48 old awk considers extra_args to be arguments to "sprintf";
50 new awk considers them arguments to "print".
51 "Considerations"
53 A2p cannot do as good a job translating as a human would, but it usu‐
55 ally does pretty well. There are some areas where you may want to
56 examine the perl script produced and tweak it some. Here are some of
57 them, in no particular order.
58 There is an awk idiom of putting int() around a string expression to
60 force numeric interpretation, even though the argument is always inte‐
61 ger anyway. This is generally unneeded in perl, but a2p can't tell if
62 the argument is always going to be integer, so it leaves it in. You
63 may wish to remove it.
64 Perl differentiates numeric comparison from string comparison. Awk has
66 one operator for both that decides at run time which comparison to do.
67 A2p does not try to do a complete job of awk emulation at this point.
68 Instead it guesses which one you want. It's almost always right, but
69 it can be spoofed. All such guesses are marked with the comment
70 ""#???"". You should go through and check them. You might want to run
71 at least once with the -w switch to perl, which will warn you if you
72 use == where you should have used eq.
73 Perl does not attempt to emulate the behavior of awk in which nonexis‐
75 tent array elements spring into existence simply by being referenced.
76 If somehow you are relying on this mechanism to create null entries for
77 a subsequent for...in, they won't be there in perl.
78 If a2p makes a split line that assigns to a list of variables that
80 looks like (Fld1, Fld2, Fld3...) you may want to rerun a2p using the -n
81 option mentioned above. This will let you name the fields throughout
82 the script. If it splits to an array instead, the script is probably
83 referring to the number of fields somewhere.
84 The exit statement in awk doesn't necessarily exit; it goes to the END
86 block if there is one. Awk scripts that do contortions within the END
87 block to bypass the block under such circumstances can be simplified by
88 removing the conditional in the END block and just exiting directly
89 from the perl script.
90 Perl has two kinds of array, numerically-indexed and associative. Perl
92 associative arrays are called "hashes". Awk arrays are usually trans‐
93 lated to hashes, but if you happen to know that the index is always
94 going to be numeric you could change the {...} to [...]. Iteration
95 over a hash is done using the keys() function, but iteration over an
96 array is NOT. You might need to modify any loop that iterates over
97 such an array.
98 Awk starts by assuming OFMT has the value %.6g. Perl starts by assum‐
100 ing its equivalent, $#, to have the value %.20g. You'll want to set $#
101 explicitly if you use the default value of OFMT.
102 Near the top of the line loop will be the split operation that is
104 implicit in the awk script. There are times when you can move this
105 down past some conditionals that test the entire record so that the
106 split is not done as often.
107 For aesthetic reasons you may wish to change the array base $[ from 1
109 back to perl's default of 0, but remember to change all array sub‐
110 scripts AND all substr() and index() operations to match.
111 Cute comments that say "# Here is a workaround because awk is dumb" are
113 passed through unmodified.
114 Awk scripts are often embedded in a shell script that pipes stuff into
116 and out of awk. Often the shell script wrapper can be incorporated
117 into the perl script, since perl can start up pipes into and out of
118 itself, and can do other things that awk can't do by itself.
119 Scripts that refer to the special variables RSTART and RLENGTH can
121 often be simplified by referring to the variables $`, $& and $', as
122 long as they are within the scope of the pattern match that sets them.
123 The produced perl script may have subroutines defined to deal with
125 awk's semantics regarding getline and print. Since a2p usually picks
126 correctness over efficiency. it is almost always possible to rewrite
127 such code to be more efficient by discarding the semantic sugar.
128 For efficiency, you may wish to remove the keyword from any return
130 statement that is the last statement executed in a subroutine. A2p
131 catches the most common case, but doesn't analyze embedded blocks for
132 subtler cases.
133 ARGV[0] translates to $ARGV0, but ARGV[n] translates to $ARGV[$n]. A
135 loop that tries to iterate over ARGV[0] won't find it.
136
138 A2p uses no environment variables.
139
141 Larry Wall <larry@wall.org>
142
145 perl The perl compiler/interpreter
146 s2p sed to perl translator
148
151 It would be possible to emulate awk's behavior in selecting string ver‐
152 sus numeric operations at run time by inspection of the operands, but
153 it would be gross and inefficient. Besides, a2p almost always guesses
154 right.
155 Storage for the awk syntax tree is currently static, and can run out.
157perl v5.8.8 2005-04-04 A2P(1)