我正在玩
study，一个Perl功能来检查一个字符串，使后续的正则表达式可能更快：
while( <> ) {
study;
$count++ if /PATTERN/;
$count++ if /OTHER/;
$count++ if /PATTERN2/;
}
关于哪些情况将从中受益匪浅？你可以从the docs中挑选出几件事情：
>具有恒定字符串的模式
>多种模式
>较短的目标字符串可能会更好(需要较少的学习时间)
我正在寻找具体的案例，我不仅可以表现出很大的优势，而且还可以稍微调整以弥补这一优势。 the docs年的警告之一是您应该对个别情况进行基准测试。我想找到一些边缘情况，一个字符串(或模式)的小差异在性能上有很大差异。
如果没有使用study，请不要回答。我宁愿拥有正确的答案，而不是快速猜测。这里没有紧迫性，这并不妨碍任何工作。
而且，作为一个奖励，我一直在使用比较两个NYTProf运行的基准测试工具，我宁愿使用通常的基准测试工具。如果我想出了一种自动化的方法，我也会分享。
解决方法
谷歌提出了这个
lovely test scenario：
#!/usr/bin/perl
#
# Exercise 7.8
#
# This is a more difficult exercise. The study function in Perl may speed up searches
# for motifs in DNA or protein. Read the Perl documentation on this function. Its use
# is simple: given some sequence data in a variable $sequence,type:
#
# study $sequence;
#
# before doing the searches. Do you think study will speed up searches in DNA or
# protein,based on what you've read about it in the documentation?
#
# For lots of extra credit! Now read the Perl documentation on the standard module
# Benchmark. (Type perldoc Benchmark,or visit the Perl home page at http://www.
# perl.com.) See if your guess is right by writing a program that benchmarks motif
# searches of DNA and of protein,with and without study.
#
# Answer to Exercise 7.8
use strict;
use warnings;
use Benchmark;
my $dna = join ('',qw(
agatggcggcgctgaggggtcttgggggctctaggccggccacctactgg
tttgcagcggagacgacgcatggggcctgcgcaataggagtacgctgcct
gggaggcgtgactagaagcggaagtagttgtgggcgcctttgcaaccgcc
tgggacgccgccgagtggtctgtgcaggttcgcgggtcgctggcgggggt
cgtgagggagtgcgccgggagcggagatatggagggagatggttcagacc
cagagcctccagatgccggggaggacagcaagtccgagaatggggagaat
gcgcccatctactgcatctgccgcaaaccggacatcaactgcttcatgat
cgggtgtgacaactgcaatgagtggttccatggggactgcatccggatca
ctgagaagatggccaaggccatccgggagtggtactgtcgggagtgcaga
gagaaagaccccaagctagagattcgctatcggcacaagaagtcacggga
gcgggatggcaatgagcgggacagcagtgagccccgggatgagggtggag
ggcgcaagaggcctgtccctgatccagacctgcagcgccgggcagggtca
gggacaggggttggggccatgcttgctcggggctctgcttcgccccacaa
atcctctccgcagcccttggtggccacacccagccagcatcaccagcagc
agcagcagcagatcaaacggtcagcccgcatgtgtggtgagtgtgaggca
tgtcggcgcactgaggactgtggtcactgtgatttctgtcgggacatgaa
gaagttcgggggccccaacaagatccggcagaagtgccggctgcgccagt
gccagctgcgggcccgggaatcgtacaagtacttcccttcctcgctctca
ccagtgacgccctcagagtccctgccaaggccccgccggccactgcccac
ccaacagcagccacagccatcacagaagttagggcgcatccgtgaagatg
agggggcagtggcgtcatcaacagtcaaggagcctcctgaggctacagcc
acacctgagccactctcagatgaggaccta
));
my $protein = join('',qw(
MNIDDKLEGLFLKCGGIDEMQSSRTMVVMGGVSGQSTVSGELQD
SVLQDRSMPHQEILAADEVLQESEMRQQDMISHDELMVHEETVKNDEEQMETHERLPQ
GLQYALNVPISVKQEITFTDVSEQLMRDKKQIR
));
my $count = 1000;
print "DNA pattern matches without 'study' function:\n";
timethis($count,' for(my $i=1 ; $i < 10000; ++$i) {
$dna =~ /aggtc/;
$dna =~ /aatggccgt/;
$dna =~ /gatcgatcagctagcat/;
$dna =~ /gtatgaac/;
$dna =~ /[ac][cg][gt][ta]/;
$dna =~ /ccccccccc/;
} '
);
print "\nDNA pattern matches with 'study' function:\n";
timethis($count,' study $dna;
for(my $i=1 ; $i < 10000; ++$i) {
$dna =~ /aggtc/;
$dna =~ /aatggccgt/;
$dna =~ /gatcgatcagctagcat/;
$dna =~ /gtatgaac/;
$dna =~ /[ac][cg][gt][ta]/;
$dna =~ /ccccccccc/;
} '
);
print "\nProtein pattern matches without 'study' function:\n";
timethis($count,' for(my $i=1 ; $i < 10000; ++$i) {
$protein =~ /PH.EI/;
$protein =~ /KFTEQGESMRLY/;
$protein =~ /[YAL][NVP][ISV][KQE]/;
$protein =~ /DKKQIR/;
$protein =~ /[MD][VT][HQ][ER]/;
$protein =~ /NVPISVKQEITFTDVSEQL/;
} '
);
print "\nProtein pattern matches with 'study' function:\n";
timethis($count,' study $protein;
for(my $i=1 ; $i < 10000; ++$i) {
$protein =~ /PH.EI/;
$protein =~ /KFTEQGESMRLY/;
$protein =~ /[YAL][NVP][ISV][KQE]/;
$protein =~ /DKKQIR/;
$protein =~ /[MD][VT][HQ][ER]/;
$protein =~ /NVPISVKQEITFTDVSEQL/;
} '
);
请注意，对于最有利可图的情况(蛋白质匹配)，报告的收益仅为约2％：
# $ perl exer07.08 # On my computer,this is the output I get: your results probably vary. # DNA pattern matches without 'study' function: # timethis 1000: 29 wallclock secs (29.25 usr + 0.00 sys = 29.25 cpu) @ 34.19/s (n=1000) # # DNA pattern matches with 'study' function: # timethis 1000: 30 wallclock secs (29.21 usr + 0.15 sys = 29.36 cpu) @ 34.06/s (n=1000) # # Protein pattern matches without 'study' function: # timethis 1000: 32 wallclock secs (29.47 usr + 0.04 sys = 29.51 cpu) @ 33.89/s (n=1000) # # Protein pattern matches with 'study' function: # timethis 1000: 30 wallclock secs (28.97 usr + 0.02 sys = 28.99 cpu) @ 34.49/s (n=1000) #