Description
tail without
options displays the last ten lines of file. The display is useful for seeing the most recent
entries in log files and any file where new information is added on
the end.
The tail command is used
with text files. To make a binary file input to the tail command,
use the –c option. If a binary file is input
without the –c option being specified, the
entire file is sent to the screen.
If
you do not specify a file, or if you specify - as the file name, tail reads
from the standard input (stdin).
Options
- ±number
- Is either of the following:
- +number
- Skips to line number and then displays
the rest of the file. For example, +100 prints from
line 100 to the end of the file.
- –number
- Prints number lines from the end of
the file. For example, -20 prints the last 20 lines
in the file.
You can precede or follow both +number and –number with
one of the following letters to indicate the unit to be used: - b–blocks
- c–bytes
- k–kilobytes
- l or n–lines
- m–megabytes
The default unit is lines.
- –B
- Disables the automatic conversion of tagged files. This option
is ignored if the filecodeset or pgmcodeset options
(-W option) are specified.
- –f
- Monitors a file as it grows. Every two seconds, tail wakes
up and prints any new data at the end of the file. This option is
ignored if tail read from the standard input,
and standard input is a pipe.
- -W option[,option]...
- Specifies z/OS-specific options. The option keywords are case-sensitive. Possible
options are:
- filecodeset=codeset
- Performs text conversion from one code set to another when reading
from the file. The coded character set of the file is codeset. codeset can
be a code set name known to the system or a numeric coded character
set identifier (CCSID). Note that the command iconv -l lists
existing CCSIDs along with their corresponding code set names. The filecodeset and pgmcodeset options
can be used on files with any file tag.
If pgmcodeset is
specified but filecodeset is omitted, then
the default file code set is ISO8859-1 even if the file is tagged
with a different code set. If neither filecodeset nor pgmcodeset is
specified, text conversion will not occur unless automatic conversion
is enabled or the _TEXT_CONV environment variable indicates text conversion.
For more information about text conversion, see Controlling text conversion for z/OS UNIX shell commands.
If filecodeset or pgmcodeset is
specified, then automatic conversion is disabled for this command
invocation and the -B option is ignored
if it is also specified. See z/OS UNIX System Services Planning for
more information about automatic conversion.
When specifying values for filecodeset,
use the values that Unicode Service supports. For more information
about supported code sets, see z/OS Unicode Services User's Guide and Reference.
- pgmcodeset=codeset
- Performs text conversion from one code set to another when reading
from the file. The coded character set of the program (command) is codeset. codeset can
be a code set name known to the system or a numeric coded character
set identifier (CCSID). Note that the command iconv -l lists
existing CCSIDs along with their corresponding code set names. The filecodeset and pgmcodeset options
can be used on files with any file tag.
If filecodeset is
specified but pgmcodeset is omitted, then
the default program code set is IBM-1047. If neither filecodeset nor pgmcodeset is
specified, text conversion will not occur unless automatic conversion
is enabled or the _TEXT_CONV environment variable indicates text conversion.
For more information about text conversion, see Controlling text conversion for z/OS UNIX shell commands.
If filecodeset or pgmcodeset is
specified, then automatic conversion is disabled for this command
invocation and the -B option is ignored
if it is also specified. See z/OS UNIX System Services Planning for
more information about automatic conversion.
Restriction: The
only supported values for pgmcodeset are
IBM-1047 and 1047.
Examples
- To display the last 10 lines of a text file to the standard output
(stdout):
tail myTextFile
- To display the last line of a text file and then monitor the file
for updates (display new data written to the text file):
tail -f -n -1 myTextFile
- To display the last 200 bytes of a text file containing UTF-8 characters to the standard output (stdout),
assuming that:
- To display a text file containing EBCDIC characters starting at
line 25, assuming that automatic conversion has been enabled but the
text file is incorrectly tagged as ASCII:
tail -B -n +25 myMisTaggedFile
Localization
tail uses
the following localization environment variables:
- LANG
- LC_ALL
- LC_CTYPE
- LC_MESSAGES
- NLSPATH
See Localization for more
information.
Environment variables
tail uses
the following environment variable:
- _TEXT_CONV
- Contains text conversion information for the command. The text
conversion information is not used when either the -B option
or the filecodeset or pgmcodeset option
(-W option) is specified. For more information
about text conversion, see Controlling text conversion for z/OS UNIX shell commands.
Exit values
- 0
- Successful completion
- 1
- Failure due to any of the following:
- Insufficient memory
- Write error on the standard output (stdout)
- Badly formed line or character count
- Missing number after an option
- Error reopening a file descriptor
- The code set is not valid
- Could not turn off automatic conversion
- Could not perform requested text conversion
- 2
- Failure due to an unknown command-line option
Messages
Possible error messages include:
- Badly formed line/character count string
- In an option of the form –n number or –number,
the number was not a valid number.
- Reopening file descriptor number
- –f was used to follow a file as it grew. tail closed
the file associated with the given file descriptor number and
then tried to open it 2 seconds later. At this point, tail found
it could not reopen the file for reading, and therefore could not
follow the file any longer.
Portability
POSIX.2, X/Open Portability Guide, UNIX systems.
The POSIX standard included only the –f, –c ±number,
and –n ±number options.
The use of b, c and l as
a ±number suffix
is considered obsolete. All other options and suffixes are extensions
of the POSIX standard.
Related information
cat, head, more