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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 302562480 by alister on Friday 7th of October 2011 04:24:30 AM
Old 10-07-2011
Quote:
Originally Posted by ygemici
if the search pattern is near the at the beginning of the file "tail -r" does needs more time.
Code:
sed operates by performing the following cycle on each line of input: 
first, sed reads one line from the input stream, removes any trailing newline, and places it in the pattern space.

so tail or "tail -r" is always may not be the best solution to just sed without pipe.

regards
ygemici
You are mistaken. Take a close look at the original code provided by the OP. It counts from the end of the file until the first match from the end.

Any approach that begins at the beginning of the file would have to read every line in the file for two reasons:

1) To be certain that the last match (first from the end of the file) has been found
2) The total number of lines in the file would be necessary to calculate a line number indexed from the end of the file (NR - x + 1).

Regards,
Alister
 

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LEARN ABOUT DEBIAN

gnupod_search

GNUPOD_SEARCH(1)						   User Commands						  GNUPOD_SEARCH(1)

NAME

       gnupod_search - search and remove files

SYNOPSIS

       gnupod_search [OPTION]...

DESCRIPTION

       Search and Remove files

       --help display this help and exit

       --version
	      output version information and exit

       -m, --mount=DIRECTORY
	      iPod mountpoint. Default is $IPOD_MOUNTPOINT

       -t, --title=STRING
	      search songs by Title

       -a, --artist=STRING
	      search songs by Artist

       -l, --album=STRING
	      search songs by Album

       -i, --id=INT
	      search songs by ID

       -g, --genre=STRING
	      search songs by Genre

       -c, --playcount=COUNT
	      search songs by Playcount

       -s, --rating=STARS
	      search songs by Rating (1 star = 20, 2 stars = 40 ...)

       -R, --podcastrss=RSS
	      search songs by podcast-rss

       -U, --podcastguid=GUID
	      search songs by podcast-guid

       -b, --bitrate=BITRATE
	      search songs by Bitrate

       -o, --match-once
	      Search does not need to match multiple times (like ($a || $b || $c))

       --delete
	      Remove (!) matched songs from the iPod

       --view=ialt
	      Modify output, default is 'ialt'

	      t = title    a = artist	r = rating	p = path

	      l = album    g = genre	c = playcount	i = id

       --rename="KEY=VALUE"
	      Rename KEY into VALUE for matched songs.

	      Example: Rename the Artist 'Jon Doe' into 'John Doe'

	      gnupod_search --artist="Jon Doe" --rename="artist=John Doe"

AUTHOR

       Written by Adrian Ulrich

REPORTING BUGS

       Report bugs to <bug-gnupod@nongnu.org>

COPYRIGHT

       Copyright (C) Adrian Ulrich
       This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
       LAR PURPOSE.

SEE ALSO

       The full documentation for gnupod is maintained as a Texinfo manual.  If the info program and GNUpod are properly installed at  your  site,
       the command

	      info gnupod

       should give you access to the complete manual.

gnupod_search 1.00						     June 2005							  GNUPOD_SEARCH(1)
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