The pithy ruminations from Edward Ned Harvey <lop...@nedharvey.com> with the subject "Re: [lopsa-discuss] Stupid sed question, or, Is sed even the smartest way to do this?" were:
=> > From: discuss-boun...@lopsa.org [mailto:discuss-boun...@lopsa.org] On => > Behalf Of Trey Darley Let's => > say it's a logfile. Suppose that you wanted to access an arbitrary => > range => > of lines, say, lines 10,000 - 13,000. One way of doing this is: => > => > <snip> => > sed -n 10000,13000p foobar.txt => > </snip> => => Inside a process, the process can seek() to a specific byte number in a => file, but if you're looking for a specific range of line numbers, and the => line length is variable, then there's no way to jump directly to a specific => line number. The only option is to do as you're doing - read from the => beginning of the file, and scan for \n characters and count line numbers. => => It's possible, maybe, that sed has an inefficient algorithm to do this. But => I doubt it. => I'd also guess that sed is going to be the best balance of program efficiency and transparency (for the admin, for troubleshooting, for future maintenance). If the performance is still unacceptable, then I'd consider writing a program that does something like this horrible mish-mash of pseudo code: ================================================= LINESZ=80 # emperically determined average line # length of logfile start=argv[0] end=argv[1] start=start-5 # provide some overlap, adjust as needed end=end+5 # turn user-supplied start & end line numbers into byte # range start=start*LINESZ end=end*LINESZ logfile=open(LOGFILE) seek(start) # seek() to the approx line # skip to the next new line while(currentchar != '\n') { currentchar=read(start) start++ } start++ # print data in the requested range while(start <= end) { printf('%s',read(start)) start++ } # print to the end of the current line while(currentchar != '\n') { currentchar=read(start) printf('%s',currentchar) start++ } printf('\n') ==================================================== Having typed that horrible example, I'd still use sed. Mark ----- Mark Bergman Biker, Rock Climber, Unix mechanic, IATSE #1 Stagehand '94 Yamaha GTS1000A^2 berg...@panix.com http://wwwkeys.pgp.net:11371/pks/lookup?op=get&search=bergman%40panix.com I want a newsgroup with a infinite S/N ratio! Now taking CFV on: rec.motorcycles.stagehands.pet-bird-owners.pinballers.unix-supporters 15+ So Far--Want to join? Check out: http://www.panix.com/~bergman _______________________________________________ Discuss mailing list Discuss@lopsa.org http://lopsa.org/cgi-bin/mailman/listinfo/discuss This list provided by the League of Professional System Administrators http://lopsa.org/
