Reading a pattern and a number of lines after it

I was recently challenged to code a program in as few lines as possible by a friend. The challenge, to read a file and look for a pattern in a line. If it found it, then the program would print that full line and a number of lines after it.

After some thought, I came up with the script below:

open(T,"<$ARGV[0]");
my (@data,$count);
foreach((@data = <T>)){++$count;(/$ARGV[1]/)?eval{print;for(1..$ARGV[2
+]){print $data[$count] if defined $data[++$count];};exit()} : undef;}
close(T);
[download]

The data file contained:

one
two
thrtestee
four
five
six
werwr
werwer
seen?
[download]

And the program was invoked as

# perl -w script.pl datafile pattern numlines
perl -w script.pl data.dat test 4
[download]

I wondered if this could be improved upon at all or if there were any unusual tricks I could have used. Had fun anyway :)

Comment on Reading a pattern and a number of lines after it Select or Download Code

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Re: Reading a pattern and a number of lines after it by blakem (Monsignor) on Jan 09, 2002 at 04:45 UTC
With a pattern of /ou/ and numlines set to 3 I get: `perl -ne '$x=/ou/..0; print if $x && $x-1 <= 3' data.dat` [download] As in: `% cat data.dat one two thrtestee four five six werwr werwer seen? % perl -ne '$x=/ou/..0; print if $x && $x-1 <= 3' data.dat four five six werwr` [download] Notice how it prints the matching line plus an additional $numlines lines... -Blake	[reply] [d/l] [select]
Re: Re: Reading a pattern and a number of lines after it by simon.proctor (Vicar) on Jan 09, 2002 at 05:13 UTC
thanks :) Looks like I have still got quite a few tricks to learn!	[reply]
Re: Reading a pattern and a number of lines after it by jryan (Vicar) on Jan 09, 2002 at 05:39 UTC
Shenanagians! I call Shenanagians! blakem broke the rules ;) The original stipulations stated that the arguments would be supplied via command line; here is the shortest I came up with with that: `open(T,"$ARGV[0]"); foreach(@_=<T>){/$ARGV[1]/?print@_[$c..$ARGV[2+$c],exit:$c++} close(T)` [download] Unfortunately, much space is taken up by the `$ARGV`. Also, note that by changing the exit to a "\n" (or removing it completely) will cause the code will print `$ARGV[2]` lines for ALL matches. Leaving the exit causes only the first batch to print. Update: I can cheat too (using blakem's arguments as an example): `perl -ne "print((<>)[0..3])if/ou/" test.txt` [download] and completely floor him; but, as I said, that would be cheating ;)	[reply] [d/l] [select]
Re (tilly) 2: Reading a pattern and a number of lines after it by tilly (Archbishop) on Jan 09, 2002 at 06:25 UTC
You didn't print the line that the match was on, which was stipulated. I also don't like having it wait forever for more input files. A better cheating solution is therefore: `perl -ne'die$_,(<>)[0..3]if/ou/' test.txt` [download] (Erm, OK. I may have just printed to the wrong filehandle... :-)	[reply] [d/l]
Re: Re (tilly) 2: Reading a pattern and a number of lines after it by jryan (Vicar) on Jan 09, 2002 at 06:37 UTC
I stand corrected; your cheating solution through the use of additional cheating is much better than mine! I just whipped mine up real quick to spite blakem, I didn't check it as thoroughly as I should :)	[reply]
Re: Reading a pattern and a number of lines after it by Juerd (Abbot) on Jan 09, 2002 at 07:03 UTC
Using $0 file pattern number, just like the original `($r,$i,$l,@ARGV)=@ARGV[1,2,2,0];(/$r/and$i='.'or++$i<=$l)&&print while +<>` [download] `2;0 juerd@ouranos:~$ perl -e'undef christmas' Segmentation fault 2;139 juerd@ouranos:~$` [download]	[reply] [d/l] [select]