Re: How to print the lines immediately above and below a matching line?

in reply to How to print the lines immediately above and below a matching line?

TMTOWTDI answer. :-)

Instead of reading the file line by line as suggested in other answers above, you could also read the entire file into a scalar and use a multi line regexp to do it. Look up use of the /m option on regexp matching.

Any Monk who wishes to extend this thread with a complete answer using this method is more than welcome to do so (I'm a bit short of time)

A Monk aims to give answers to those who have none, and to learn from those who know more.

Comment on Re: How to print the lines immediately above and below a matching line?

Re^2: How to print the lines immediately above and below a matching line?
by Anonymous Monk on Nov 25, 2012 at 16:33 UTC

If at ever there will need to be printed most at then some three lines, read the whole file is waste of memory

[reply]

Re^3: How to print the lines immediately above and below a matching line?

by roboticus (Canon) on Nov 25, 2012 at 18:38 UTC

Waste of memory? Memory is there to be used ... what are you saving it for?

Sure, for a long-lived application may want to be leery of using a large quantity of ram. But if it solves the immediate problem at hand, then using memory isn't really a problem. Also, memory is so large anymore that you need to work with *big* files if you're going to make memory usage a problem. The ordinary file isn't really going to be a problem.

For example, here's a histogram of file sizes on a couple of my machines--my work laptop (LT0186) and my goofing off computer (Boink):

files smallar than	LT0186	Boink
1	2852	122103
10	701	5777
25	3920	30988
50	7793	31843
100	4501	41932
250	10112	128614
500	14385	119923
1k	31564	192614
2.5k	40133	275173
5k	33471	218245
10k	34710	233223
25k	27628	211316
50k	14394	100595
100k	12579	71556
250k	9674	61003
500k	4961	22754
1M	3508	13800
2.5M	2013	8325
5M	852	4279
10M	738	4586
25M	365	1958
50M	223	634
100M	54	372
250M	52	129
500M	22	63
1G	16	55
2.5G	9	32
5G	0	3
10G	0	1

I wouldn't take a second thought about just loading a file under 500M into RAM, and as you can see, I have *very few* files larger than that. And for a simple task like the one presented, I'd probably go ahead and try it on larger files (swap space permitting) and go take a break.

...roboticus

When your only tool is a hammer, all problems look like your thumb.

[reply]

Re^4: How to print the lines immediately above and below a matching line?

by Anonymous Monk on Nov 25, 2012 at 18:42 UTC

Waste of memory? Memory is there to be used ... what are you saving it for?

seriously? This entire "program" is a joke -- grep does it already

[reply]

Re^5: How to print the lines immediately above and below a matching line?

by roboticus (Canon) on Nov 25, 2012 at 19:16 UTC

Re^6: How to print the lines immediately above and below a matching line?

by Anonymous Monk on Nov 26, 2012 at 09:42 UTC