/usr/bin/tail [±s number [lbcr]] [file]
/usr/bin/tail [-lbcr] [file]
/usr/bin/tail [± number [lbcf]] [file]
/usr/bin/tail [-lbcf] [file]
/usr/xpg4/bin/tail [-f | -r] [-c number | -n number] [file]
/usr/xpg4/bin/tail [± number [l | b | c] [f]] [file]
/usr/xpg4/bin/tail [± number [l] [f | r]] [file]
tail [options]] [file ...]
The tail utility copies the named file to the standard output beginning at a designated place. If no file is named, the standard input is used.
Copying begins at a point in the file indicated by the -cnumber, -nnumber, or ±number options (if +number is specified, begins at distance number from the beginning; if -number is specified, from the end of the input; if number is NULL, the value 10 is assumed). number is counted in units of lines or byte according to the -c or -n options, or lines, blocks, or bytes, according to the appended option l, b, or c. When no units are specified, counting is by lines.
tail copies one or more input files to standard output starting at a designated point for each file. Copying starts at the point indicated by the options and is unlimited in size.
By default a header of the form ==> filename <== is output before all but the first file but this can be changed with the -q and -v options.
If no file is given, or if the file is -, tail copies from standard input. The start of the file is defined as the current offset.
The option argument for -c can optionally be followed by one of the following characters to specify a different unit other than a single byte:
-c counts in bytes and not in characters (which affects texts using multi-byte characters).
For backwards compatibility, -number is equivalent to -n number and +number is equivalent to -n -number.
The -b option is obsolete because of the general non-portability of block-sized units of text.
This command conforms to IEEE Std 1003.1-2008.
The following options are supported for both /usr/bin/tail and /usr/xpg4/bin/tail. The -r and -f options are mutually exclusive. If both are specified on the command line, the -f option is ignored.
Units of blocks.
Units of bytes.
Follow. If the input-file is not a pipe, the program does not terminate after the line of the input-file has been copied, but enters an endless loop, wherein it sleeps for a second and then attempts to read and copy further records from the input-file. Thus it can be used to monitor the growth of a file that is being written by some other process.
Units of lines.
Reverse. Copies lines from the specified starting point in the file in reverse order. The default for r is to print the entire file in reverse order.
The following options are supported for /usr/xpg4/bin/tail only:
The number option-argument must be a decimal integer whose sign affects the location in the file, measured in bytes, to begin the copying:
Copying starts relative to the beginning of the file.
Copying starts relative to the end of the file.
Copying starts relative to the end of the file.
The origin for counting is 1; that is, -c+1 represents the first byte of the file, -c-1 the last.
Equivalent to -cnumber, except the starting location in the file is measured in lines instead of bytes. The origin for counting is 1. That is, -n+1 represents the first line of the file, -n-1 the last.
The following options are supported for the ksh93 built-in version of tail. The -r and -f options are mutually exclusive. If both are specified on the command line, the -f option is ignored.
Copy lines from each file. A negative value for lines indicates an offset from the end of the file. The default value is 10.
Copy units of 512 bytes (Obsolete).
Copy chars bytes from each file. A negative value for chars indicates an offset from the end of the file. The option value may be omitted.
Loop forever trying to read more characters as the end of each file to copy new data. Ignored if reading from a pipe or fifo.
Output filename headers. On by default. -h means --noheaders.
Copy units of lines. This is the default.
When a --forever file times out via --timeout, verify that the current file has not been renamed and replaced by another file of the same name (a common log file practice) before giving up on the file.
Don't output filename headers. For GNU compatibility.
Output lines in reverse order.
Don't warn about timeout expiration and log file changes.
Stop checking after timeout elapses with no additional --forever output. A separate elapsed time is maintained for each file operand. There is no timeout by default. The default timeout unit is seconds. timeout may be a catenation of 1 or more integers, each followed by a 1 character suffix. The suffix may be omitted from the last integer, in which case it is interpreted as seconds. The supported suffixes are:
Prints basic help information.
Prints built-in manual page in either plain text, HTML or nroff format.
Prints version information.
The following operand is supported:
A path name of an input file. If no file operands are specified, the standard input is used.
See largefile(5) for the description of the behavior of tail when encountering files greater than or equal to 2 Gbyte ( 231 bytes).
The following command prints the last ten lines of the file fred, followed by any lines that are appended to fred between the time tail is initiated and killed.
example% tail -f fred
The next command prints the last 15 bytes of the file fred, followed by any lines that are appended to fred between the time tail is initiated and killed:
example% tail -15cf fred
See environ(5) for descriptions of the following environment variables that affect the execution of tail: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, and NLSPATH.
See attributes(5) for descriptions of the following attributes:
IEEE Std 1003.1-2008
Piped tails relative to the end of the file are stored in a buffer, and thus are limited in length. Various kinds of anomalous behavior can happen with character special files.