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1 perry 1 A2P
2 !!!A2P
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 ENVIRONMENT
7 AUTHOR
8 FILES
9 SEE ALSO
10 DIAGNOSTICS
11 BUGS
12 ----
13 !!NAME
14
15
16 a2p - Awk to Perl translator
17 !!SYNOPSIS
18
19
20 __a2p [[options] filename__
21 !!DESCRIPTION
22
23
24 ''A2p'' takes an awk script specified on the command line
25 (or from standard input) and produces a comparable
26 ''perl'' script on the standard output.
27
28
29 __Options__
30
31
32 Options include:
33
34
35 __-D__
36
37
38 sets debugging flags.
39
40
41 __-F__
42
43
44 tells a2p that this awk script is always invoked with this
45 __-F__ switch.
46
47
48 __-n__
49
50
51 specifies the names of the input fields if input does not
52 have to be split into an array. If you were translating an
53 awk script that processes the password file, you might
54 say:
55
56
57 a2p -7 -nlogin.password.uid.gid.gcos.shell.home
58 Any delimiter can be used to separate the field names.
59
60
61 __-__
62
63
64 causes a2p to assume that input will always have that many
65 fields.
66
67
68 __-o__
69
70
71 tells a2p to use old awk behavior. The only current
72 differences are:
73
74
75 Old awk always has a line loop, even if there are no line
76 actions, whereas new awk does not.
77
78
79 In old awk, sprintf is extremely greedy about its arguments.
80 For example, given the statement
81
82
83 print sprintf(some_args), extra_args;
84 old awk considers ''extra_args'' to be arguments to sprintf; new awk considers them arguments to print.
85
86
87 __``Considerations''__
88
89
90 A2p cannot do as good a job translating as a human would,
91 but it usually does pretty well. There are some areas where
92 you may want to examine the perl script produced and tweak
93 it some. Here are some of them, in no particular
94 order.
95
96
97 There is an awk idiom of putting ''int()'' around a
98 string expression to force numeric interpretation, even
99 though the argument is always integer anyway. This is
100 generally unneeded in perl, but a2p can't tell if the
101 argument is always going to be integer, so it leaves it in.
102 You may wish to remove it.
103
104
105 Perl differentiates numeric comparison from string
106 comparison. Awk has one operator for both that decides at
107 run time which comparison to do. A2p does not try to do a
108 complete job of awk emulation at this point. Instead it
109 guesses which one you want. It's almost always right, but it
110 can be spoofed. All such guesses are marked with the comment
111 #???
112 -w__
113 switch to perl, which will warn you if you use == where you
114 should have used eq.
115
116
117 Perl does not attempt to emulate the behavior of awk in
118 which nonexistent array elements spring into existence
119 simply by being referenced. If somehow you are relying on
120 this mechanism to create null entries for a subsequent
121 for...in, they won't be there in perl.
122
123
124 If a2p makes a split line that assigns to a list of
125 variables that looks like (Fld1, Fld2, Fld3...) you may want
126 to rerun a2p using the __-n__ option mentioned above.
127 This will let you name the fields throughout the script. If
128 it splits to an array instead, the script is probably
129 referring to the number of fields somewhere.
130
131
132 The exit statement in awk doesn't necessarily exit; it goes
133 to the END block if there is one. Awk scripts
134 that do contortions within the END block to
135 bypass the block under such circumstances can be simplified
136 by removing the conditional in the END block
137 and just exiting directly from the perl script.
138
139
140 Perl has two kinds of array, numerically-indexed and
141 associative. Perl associative arrays are called ``hashes''.
142 Awk arrays are usually translated to hashes, but if you
143 happen to know that the index is always going to be numeric
144 you could change the {...} to [[...]. Iteration over a hash
145 is done using the ''keys()'' function, but iteration over
146 an array is NOT . You might need to modify
147 any loop that iterates over such an array.
148
149
150 Awk starts by assuming OFMT has the value
151 %.6g. Perl starts by assuming its equivalent, $#, to have
152 the value %.20g. You'll want to set $# explicitly if you use
153 the default value of OFMT .
154
155
156 Near the top of the line loop will be the split operation
157 that is implicit in the awk script. There are times when you
158 can move this down past some conditionals that test the
159 entire record so that the split is not done as
160 often.
161
162
163 For aesthetic reasons you may wish to change the array base
164 $[[ from 1 back to perl's default of 0, but remember to
165 change all array subscripts AND all
166 ''substr()'' and ''index()'' operations to
167 match.
168
169
170 Cute comments that say ``# Here is a workaround because awk
171 is dumb'' are passed through unmodified.
172
173
174 Awk scripts are often embedded in a shell script that pipes
175 stuff into and out of awk. Often the shell script wrapper
176 can be incorporated into the perl script, since perl can
177 start up pipes into and out of itself, and can do other
178 things that awk can't do by itself.
179
180
181 Scripts that refer to the special variables
182 RSTART and RLENGTH can often
183 be simplified by referring to the variables $`, $
184
185
186 The produced perl script may have subroutines defined to
187 deal with awk's semantics regarding getline and print. Since
188 a2p usually picks correctness over efficiency. it is almost
189 always possible to rewrite such code to be more efficient by
190 discarding the semantic sugar.
191
192
193 For efficiency, you may wish to remove the keyword from any
194 return statement that is the last statement executed in a
195 subroutine. A2p catches the most common case, but doesn't
196 analyze embedded blocks for subtler cases.
197
198
199 ARGV[[0] translates to $ARGV0, but ARGV[[n]
200 translates to $ARGV[[$n]. A loop that tries to
201 iterate over ARGV[[0] won't find it.
202 !!ENVIRONMENT
203
204
205 A2p uses no environment variables.
206 !!AUTHOR
207
208
209 Larry Wall larry@wall.org''''
210 !!FILES
211 !!SEE ALSO
212
213
214 perl The perl compiler/interpreter
215 s2p sed to perl translator
216 !!DIAGNOSTICS
217 !!BUGS
218
219
220 It would be possible to emulate awk's behavior in selecting
221 string versus numeric operations at run time by inspection
222 of the operands, but it would be gross and inefficient.
223 Besides, a2p almost always guesses right.
224
225
226 Storage for the awk syntax tree is currently static, and can
227 run out.
228 ----
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