tail

- deliver the last part of a file

Synopsis

/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]

Description

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 -c number, -n number, 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.

Options

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.

-b

Units of blocks.

-c

Units of bytes.

-f

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.

-l

Units of lines.

-r

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.

/usr/xpg4/bin/tail

The following options are supported for /usr/xpg4/bin/tail only:

-c number

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.

none

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.

-n number

Equivalent to -c number, 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.

Operands

The following operand is supported:

file

A path name of an input file. If no file operands are specified, the standard input is used.

Usage

See largefile(5) for the description of the behavior of tail when encountering files greater than or equal to 2 Gbyte (2³¹ bytes).

Examples

Example 1 Using the tail Command

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

Environment Variables

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.

Exit Status

The following exit values are returned:

0

Successful completion.

>0

An error occurred.

Attributes

See attributes(5) for descriptions of the following attributes:

/usr/bin/tail

/usr/xpg4/bin/tail

See Also

cat(1), head(1), more(1), pg(1), dd(1M), attributes(5), environ(5), largefile(5), standards(5)

Notes

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.