1A2P(1) User Contributed Perl Documentation 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:
17 -D<number>
19 sets debugging flags.
20 -F<character>
22 tells a2p that this awk script is always invoked with this -F
23 switch.
24 -n<fieldlist>
26 specifies the names of the input fields if input does not have to
27 be split into an array. If you were translating an awk script
28 that processes the password file, you might say:
29 a2p -7 -nlogin.password.uid.gid.gcos.shell.home
31 Any delimiter can be used to separate the field names.
33 -<number>
35 causes a2p to assume that input will always have that many fields.
36 -o tells a2p to use old awk behavior. The only current differences
38 are:
39 • Old awk always has a line loop, even if there are no line
41 actions, whereas new awk does not.
42 • In old awk, sprintf is extremely greedy about its arguments.
44 For example, given the statement
45 print sprintf(some_args), extra_args;
47 old awk considers extra_args to be arguments to "sprintf";
49 new awk considers them arguments to "print".
50 "Considerations"
52 A2p cannot do as good a job translating as a human would, but it
53 usually does pretty well. There are some areas where you may want to
54 examine the perl script produced and tweak it some. Here are some of
55 them, in no particular order.
56 There is an awk idiom of putting int() around a string expression to
58 force numeric interpretation, even though the argument is always
59 integer anyway. This is generally unneeded in perl, but a2p can't tell
60 if the argument is always going to be integer, so it leaves it in. You
61 may wish to remove it.
62 Perl differentiates numeric comparison from string comparison. Awk has
64 one operator for both that decides at run time which comparison to do.
65 A2p does not try to do a complete job of awk emulation at this point.
66 Instead it guesses which one you want. It's almost always right, but
67 it can be spoofed. All such guesses are marked with the comment
68 ""#???"". You should go through and check them. You might want to run
69 at least once with the -w switch to perl, which will warn you if you
70 use == where you should have used eq.
71 Perl does not attempt to emulate the behavior of awk in which
73 nonexistent array elements spring into existence simply by being
74 referenced. If somehow you are relying on this mechanism to create
75 null entries for a subsequent for...in, they won't be there in perl.
76 If a2p makes a split line that assigns to a list of variables that
78 looks like (Fld1, Fld2, Fld3...) you may want to rerun a2p using the -n
79 option mentioned above. This will let you name the fields throughout
80 the script. If it splits to an array instead, the script is probably
81 referring to the number of fields somewhere.
82 The exit statement in awk doesn't necessarily exit; it goes to the END
84 block if there is one. Awk scripts that do contortions within the END
85 block to bypass the block under such circumstances can be simplified by
86 removing the conditional in the END block and just exiting directly
87 from the perl script.
88 Perl has two kinds of array, numerically-indexed and associative. Perl
90 associative arrays are called "hashes". Awk arrays are usually
91 translated to hashes, but if you happen to know that the index is
92 always going to be numeric you could change the {...} to [...].
93 Iteration over a hash is done using the keys() function, but iteration
94 over an array is NOT. You might need to modify any loop that iterates
95 over such an array.
96 Awk starts by assuming OFMT has the value %.6g. Perl starts by
98 assuming its equivalent, $#, to have the value %.20g. You'll want to
99 set $# explicitly if you use the default value of OFMT.
100 Near the top of the line loop will be the split operation that is
102 implicit in the awk script. There are times when you can move this
103 down past some conditionals that test the entire record so that the
104 split is not done as often.
105 For aesthetic reasons you may wish to change index variables from being
107 1-based (awk style) to 0-based (Perl style). Be sure to change all
108 operations the variable is involved in to match.
109 Cute comments that say "# Here is a workaround because awk is dumb" are
111 passed through unmodified.
112 Awk scripts are often embedded in a shell script that pipes stuff into
114 and out of awk. Often the shell script wrapper can be incorporated
115 into the perl script, since perl can start up pipes into and out of
116 itself, and can do other things that awk can't do by itself.
117 Scripts that refer to the special variables RSTART and RLENGTH can
119 often be simplified by referring to the variables $`, $& and $', as
120 long as they are within the scope of the pattern match that sets them.
121 The produced perl script may have subroutines defined to deal with
123 awk's semantics regarding getline and print. Since a2p usually picks
124 correctness over efficiency. it is almost always possible to rewrite
125 such code to be more efficient by discarding the semantic sugar.
126 For efficiency, you may wish to remove the keyword from any return
128 statement that is the last statement executed in a subroutine. A2p
129 catches the most common case, but doesn't analyze embedded blocks for
130 subtler cases.
131 ARGV[0] translates to $ARGV0, but ARGV[n] translates to $ARGV[$n-1]. A
133 loop that tries to iterate over ARGV[0] won't find it.
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136 A2p uses no environment variables.
137
139 Larry Wall <larry@wall.org>
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142 perl The perl compiler/interpreter
143 s2p sed to perl translator
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147 It would be possible to emulate awk's behavior in selecting string
148 versus numeric operations at run time by inspection of the operands,
149 but it would be gross and inefficient. Besides, a2p almost always
150 guesses right.
151 Storage for the awk syntax tree is currently static, and can run out.
153perl v5.36.0 2023-01-19 A2P(1)