TAIL(1) BSD Reference Manual TAIL(1)
tail - display the last part of a file
tail [-Ff | -r] [-b number | -c number | -n number | -number] [file ...]
The tail utility displays the contents of file or, by default, its stan- dard input, to the standard output. The display begins at a byte, line, or 512-byte block location in the in- put. Numbers having a leading plus ('+') sign are relative to the begin- ning of the input, for example, -c +2 starts the display at the second byte of the input. Numbers having a leading minus ('-') sign or no expli- cit sign are relative to the end of the input, for example, -n 2 displays the last two lines of the input. The default starting location is -n 10, or the last 10 lines of the input. The options are as follows: -b number The location is number 512-byte blocks. -c number The location is number bytes. -n number | -number The location is number lines. -F Does the same as -f, for GNU compatibility, where their tail -f does not follow replaced files automatically. As a MirOS exten- sion, sets output to line-buffered even if it's not a terminal. -f Do not stop when end-of-file is reached, but rather to wait for additional data to be appended to the input. If the file is re- placed (i.e., the inode number changes), tail will reopen the file and continue. If the file is truncated, tail will reset its position to the beginning. This makes tail more useful for watch- ing log files that may get rotated. The -f option is ignored if the standard input is a pipe, but not if it is a FIFO. -r The -r option causes the input to be displayed in reverse order, by line. Additionally, this option changes the meaning of the -b, -c, and -n options. When the -r option is specified, these op- tions specify the number of bytes, lines or 512-byte blocks to display, instead of the bytes, lines, or blocks from the begin- ning or end of the input from which to begin the display. The de- fault for the -r option is to display all of the input. If more than a single file is specified, each file is preceded by a header consisting of the string "==> XXX <==" where "XXX" is the name of the file. The tail utility exits 0 on success or >0 if an error occurred.
To display the last 500 lines of the file foo: $ tail -500 foo Keep /var/log/messages open, displaying to the standard output anything appended to the file: $ tail -f /var/log/messages
cat(1), head(1), sed(1)
The tail utility is expected to be a superset of the IEEE Std 1003.2-1992 ("POSIX.2") specification. In particular, the -b and -r options are ex- tensions to that standard. The historic command line syntax of tail is supported by this implementa- tion. The only difference between this implementation and historic ver- sions of tail, once the command line syntax translation has been done, is that the -b, -c and -n options modify the -r option, i.e., -r -c 4 displays the last 4 characters of the last line of the input, while the historic tail (using the historic syntax -4cr) would ignore the -c option and display the last 4 lines of the input.
A tail command appeared in Version 7 AT&T UNIX. MirOS BSD #10-current May 20, 2012 1
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