Re^2: perl performance vs egrep

base on my "programming perl" 2nd edition P538, things like

if /one-hump/ || /two/; 

is likely to be faster than:

if /one-hump|two/;
[download]

so you may speed it up with this sorta regex.

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Re^3: perl performance vs egrep by demerphq (Chancellor) on Jan 24, 2005 at 08:43 UTC
Sure that is somewhat common advice. But it doesnt apply here. Consider the regex holli posted: `/^(CP\|KL\|KM\|ME\|PA\|PM\|SL\|SZ\|WX\|YZ)XX1/` [download] This allows Perls regex algorithm to exploit a number of optimizations that aren't available in your variant. First, the regex has a common constant string 'XX1' so the regex engine knows it cant match unless it finds that first (and once found it knows where to start looking to see if its a match). Second the algorithm is anchored at the start which means the search is constrained to one spot. It won't traverse the options more than once per line. The trick you showed actually allows the constant string match to work, but is still probably a touch slower than using two index calls. --- demerphq	[reply] [d/l]

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Re^3: perl performance vs egrep
by demerphq (Chancellor) on Jan 24, 2005 at 08:43 UTC

Sure that is somewhat common advice. But it doesnt apply here. Consider the regex holli posted:

/^(CP|KL|KM|ME|PA|PM|SL|SZ|WX|YZ)XX1/
[download]

This allows Perls regex algorithm to exploit a number of optimizations that aren't available in your variant. First, the regex has a common constant string 'XX1' so the regex engine knows it cant match unless it finds that first (and once found it knows where to start looking to see if its a match). Second the algorithm is anchored at the start which means the search is constrained to one spot. It won't traverse the options more than once per line.

The trick you showed actually allows the constant string match to work, but is still probably a touch slower than using two index calls.

---
demerphq

[reply]
[d/l]