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Full Discussion: Better and efficient way to reverse search a file for first matched line number.
Top Forums Shell Programming and Scripting Better and efficient way to reverse search a file for first matched line number. Post 302562462 by alister on Friday 7th of October 2011 02:09:38 AM
Old 10-07-2011
Quote:
Originally Posted by kchinnam
But it feels like I am using too many commands. Is there a better more efficiant way to do this on Unix?

...<snip>...

Code:
 
vStart='Started'; myLog=abc.log
lineNum=`/usr/xpg4/bin/tail -r $myLog | cat -n | sed -n "/$vStart/{p;q;}" | awk '{print $1}'`


You don't need to use cat or awk. Just use sed's = command (which prints the current line number).
Code:
tail -r file | sed -n '/pat/{=;q;}'

If the reason you're asking about efficiency is because it's a large file, then this tail|sed approach is much better than any awk or grep solution. Why? The other suggestions must all read the file in its entirety. tail -r will seek to the end of the file and start reading there. As soon as sed finds a matching line it will exit. This will terminate tail (via SIGPIPE).

Regards,
Alister
 

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LEARN ABOUT DEBIAN

std::sub_match

std::sub_match< _BiIter >(3cxx) 										   std::sub_match< _BiIter >(3cxx)

NAME

       std::sub_match< _BiIter > -

SYNOPSIS

       Inherits std::pair< _BiIter, _BiIter >.

   Public Types
       typedef iterator_traits
	   < _BiIter >::difference_type difference_type"
       typedef _BiIter first_type
       typedef _BiIter iterator
       typedef _BiIter second_type
       typedef std::basic_string
	   < value_type > string_type"
       typedef iterator_traits
	   < _BiIter >::value_type value_type"

   Public Member Functions
       int compare (const sub_match &__s) const
       int compare (const string_type &__s) const
       int compare (const value_type *__s) const
       difference_type length () const
       operator string_type () const
       string_type str () const
       void swap (pair &__p)

   Public Attributes
       _BiIter first
       bool matched
       _BiIter second

Detailed Description
   template<typename _BiIter>class std::sub_match< _BiIter >
       A sequence of characters matched by a particular marked sub-expression.

       An object of this class is essentially a pair of iterators marking a matched subexpression within a regular expression pattern match. Such
       objects can be converted to and compared with std::basic_string objects of a similar base character type as the pattern matched by the
       regular expression.

       The iterators that make up the pair are the usual half-open interval referencing the actual original pattern matched.

       Definition at line 757 of file regex.h.

Member Typedef Documentation
   typedef _BiIter  std::pair< _BiIter , _BiIter  >::second_type [inherited]
       first_type is the first bound type

       Definition at line 90 of file stl_pair.h.

Member Function Documentation
   template<typename _BiIter> int std::sub_match< _BiIter >::compare (const sub_match< _BiIter > &__s) const [inline]
       Compares this and another matched sequence. Parameters:
	   s Another matched sequence to compare to this one.

       Return values:
	   <0 this matched sequence will collate before s.
	   =0 this matched sequence is equivalent to s.
	   <0 this matched sequence will collate after s.

       Definition at line 818 of file regex.h.

       Referenced by std::operator!=(), std::operator<(), std::operator<=(), std::operator==(), std::operator>(), and std::operator>=().

   template<typename _BiIter> int std::sub_match< _BiIter >::compare (const string_type &__s) const [inline]
       Compares this sub_match to a string. Parameters:
	   s A string to compare to this sub_match.

       Return values:
	   <0 this matched sequence will collate before s.
	   =0 this matched sequence is equivalent to s.
	   <0 this matched sequence will collate after s.

       Definition at line 831 of file regex.h.

   template<typename _BiIter> int std::sub_match< _BiIter >::compare (const value_type *__s) const [inline]
       Compares this sub_match to a C-style string. Parameters:
	   s A C-style string to compare to this sub_match.

       Return values:
	   <0 this matched sequence will collate before s.
	   =0 this matched sequence is equivalent to s.
	   <0 this matched sequence will collate after s.

       Definition at line 844 of file regex.h.

   template<typename _BiIter> difference_type std::sub_match< _BiIter >::length () const [inline]
       Gets the length of the matching sequence.

       Definition at line 775 of file regex.h.

   template<typename _BiIter> std::sub_match< _BiIter >::operator string_type () const [inline]
       Gets the matching sequence as a string. Returns:
	   the matching sequence as a string.

       This is the implicit conversion operator. It is identical to the str() member function except that it will want to pop up in unexpected
       places and cause a great deal of confusion and cursing from the unwary.

       Definition at line 788 of file regex.h.

   template<typename _BiIter> string_type std::sub_match< _BiIter >::str () const [inline]
       Gets the matching sequence as a string. Returns:
	   the matching sequence as a string.

       Definition at line 801 of file regex.h.

       Referenced by std::sub_match< _Bi_iter >::compare(), and std::operator<<().

Member Data Documentation
   _BiIter  std::pair< _BiIter , _BiIter  >::first [inherited]
       second_type is the second bound type

       Definition at line 92 of file stl_pair.h.

       Referenced by std::sub_match< _Bi_iter >::length(), std::sub_match< _Bi_iter >::operator string_type(), and std::sub_match< _Bi_iter
       >::str().

   _BiIter  std::pair< _BiIter , _BiIter  >::second [inherited]
       first is a copy of the first object

       Definition at line 93 of file stl_pair.h.

       Referenced by std::sub_match< _Bi_iter >::length(), std::sub_match< _Bi_iter >::operator string_type(), and std::sub_match< _Bi_iter
       >::str().

Author
       Generated automatically by Doxygen for libstdc++ from the source code.

libstdc++							  Tue Nov 27 2012				   std::sub_match< _BiIter >(3cxx)
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