09-23-2016
Quote:
Originally Posted by
houmingc
what does the below unix command do?
tail -100f abcd.log
tail - output the last part of files
f- follow
100???
Hello houmingc,
Please use cods tags as per forum rules for your commands/Inputs/codes which you are using into your posts.
tailcommand is use to get last part of Input_files. So command
tail -100 Input_filewill show the last 100 lines of your Input_file.
tail -100f Input_filewill show last 100 lines of your Input_file + it will append the data of Input_file if that grows on standard output. So finally we could say,
tail -100 Input_filewill provide you last 100 lines of your Input_file and
tail -100f Input_filewill provide you last 100 lines of your Input_file with keeping the cursor on screen to wait for new/appending lines of Input_file, so mostly it is used to monitor the logs(if they are keep on growing/increasing and parallel you are doing some operation whose logs you want to monitor).
Thanks,
R. Singh
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TAIL(1) General Commands Manual TAIL(1)
NAME
tail - deliver the last part of a file
SYNOPSIS
tail [ +-number[lbc][rf] ] [ file ]
tail [ -fr ] [ -n nlines ] [ -c ncharacters ] [ file ]
DESCRIPTION
Tail copies the named file to the standard output beginning at a designated place. If no file is named, the standard input is copied.
Copying begins at position +number measured from the beginning, or -number from the end of the input. Number is counted in lines, 1K
blocks or characters, according to the appended flag or Default is -10l (ten ell).
The further flag causes tail to print lines from the end of the file in reverse order; (follow) causes tail, after printing to the end, to
keep watch and print further data as it appears.
The second syntax is that promulgated by POSIX, where the numbers rather than the options are signed.
EXAMPLES
tail file
Print the last 10 lines of a file.
tail +0f file
Print a file, and continue to watch data accumulate as it grows.
sed 10q file
Print the first 10 lines of a file.
SOURCE
/sys/src/cmd/tail.c
BUGS
Tails relative to the end of the file are treasured up in a buffer, and thus are limited in length.
According to custom, option +number counts lines from 1, and counts blocks and characters from 0.
TAIL(1)