grep using regex

xingjin3131 has asked for the wisdom of the Perl Monks concerning the following question:

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Re: grep using regex by ikegami (Patriarch) on Mar 01, 2009 at 21:12 UTC
Works for me `use strict; use warnings; my @allData = <DATA>; my @tmpHeader = grep /^Test\s+\d+\s+of\s+\d+$/../^\d+\s+end$/, @allDat +a; print @tmpHeader; __DATA__ Test 1 of 1 bala bala bala. bala 138 end blah blah` [download] `Test 1 of 1 bala bala bala. bala 138 end` [download] Please pick more meaningful titles.	[reply] [d/l] [select]
Re: grep using regex by ysth (Canon) on Mar 02, 2009 at 00:07 UTC
Because the .. flipflop operator remembers its state, you will run into problems if you use it in a loop like that and expect it to automatically reset each time you start the grep loop. That's only safe to do if you only ever run that grep once. -- Online Fortune Cookie Search Office Space merchandise	[reply]
Re: grep using regex by toolic (Bishop) on Mar 01, 2009 at 21:53 UTC
If your actual data has any whitespace at the end (other than the newline), then that could explain why you are seeing no output. When I download your data, there is no extra whitespace, but perhaps it got cropped off when you posted it (or when I downloaded it). Perhaps try looking for extra whitespace using: `@tmpHeader = grep /^Test\s+\d+\s+of\s+\d+\s*?$/../^\d+\s+end$/, @allDa +ta; ^^^^` [download]	[reply] [d/l]
Re: grep using regex (grepping with a regex) by ww (Archbishop) on Mar 01, 2009 at 21:50 UTC
Since you only sketch the actual output code, perhaps the problem is there? On the other hand, if your "print @tmpHeader" is your actual code, you might find `for my $tmpHeader(@tmpHeader) { print '[' . $tmpHeader . '] '; }` [download] more readable, when you've solved the root issue. Update: "more readable" may be irrelevant; depends on the how -- precisely -- the data you show is formatted. ikegami's use of `__DATA__` produces entirely readable output, but my initial instinct was to hardcode what you presented as: `my @allData = ('Test 1 of 1', 'bala', 'bala', ...` [download] which produces the (desired) output as a single line without distinction among the elements. Obligatory suggestion: `use strict; use warnings;` may be helpful, especially if there's a ~~slip betwixt cup and lip~~ typo between your actual code and what you posted.	[reply] [d/l] [select]
Re: grep using regex by leslie (Pilgrim) on Mar 02, 2009 at 05:09 UTC
Hi xing, Your code is working fine with this given input. But you need to use flip-flop operator very carefully. For example, if there is a file and we want to process only certain sections of it, then using the flip-flop operator the code can be written like: `while () { if (/!! START !!/ .. /!! END !!/) { # process line } }` [download] Each time around the loop, the current line is checked by the flip-flop operator. If the line doesn't match /!! START !!/ then the operator returns false and the loop continues. When we reach the first line that matches /!! START !!/ then the flip-flop operator returns true and the code in the if block is executed. On subsequent iterations of the while loop, the flip-flop operator checks for matches again /!! END !!/, but it continues to return true until it finds a match. This means that all of the lines between the "!! START !!" and "!! END !!" markers are processed. When a line matches /!! END !!/ then the flip-flop operator returns false and starts checking against the first regex again.	[reply] [d/l]