tail [ -f ] [ -c number ] [ -n number ] [ file ]
Copying begins at the point in the file indicated by the -c number or -n number options, where number is a count of bytes (-c) or lines (-n). Both line and byte counts start from 1. If number is prefixed with a plus sign (+), then number is measured from the beginning of the file: if prefixed with a minus sign (), from the end of the file. No sign causes tail to measure from the end of the file.
With the -f (``follow'') option, if the input file is not a pipe, the program will not terminate after the last line of the input file has been copied, but will enter an endless loop, in which it sleeps for a second and then attempts to read and copy further records from the input file. Thus it may be used to monitor the growth of a file that is being written by some other process. For example, the command tail -f file will print the last ten lines of file, followed by any lines that are appended to file between the time tail is initiated and killed.
In the first syntax line, ±number functions in the same way as the argument to -c and -n. The appended option suffixes cause tail to count as follows:
tail understands the option -- as the option delimiter.
ISO/IEC DIS 99452:1992, Information technology Portable Operating System Interface (POSIX) Part 2: Shell and Utilities (IEEE Std 1003.21992);
AT&T SVID Issue 2;
X/Open CAE Specification, Commands and Utilities, Issue 4, 1992.