Writing to an External Program

You can instruct tar to send the contents of each extracted file to the standard input of an external program:

--to-command=command

Extract files and pipe their contents to the standard input of command. When this option is used, instead of creating the files specified, tar invokes command and pipes the contents of the files to its standard output. Command may contain command line arguments. The program is executed via sh -c. Notice, that command is executed once for each regular file extracted. Non-regular files (directories, etc.) are ignored when this option is used.

The command can obtain the information about the file it processes from the following environment variables:

TAR_FILETYPE

Type of the file. It is a single letter with the following meaning:

f	Regular file
d	Directory
l	Symbolic link
h	Hard link
b	Block device
c	Character device

Currently only regular files are supported.

TAR_MODE

File mode, an octal number.

TAR_FILENAME

The name of the file.

TAR_REALNAME

Name of the file as stored in the archive.

TAR_UNAME

Name of the file owner.

TAR_GNAME

Name of the file owner group.

TAR_ATIME

Time of last access. It is a decimal number, representing seconds since the epoch. If the archive provides times with nanosecond precision, the nanoseconds are appended to the timestamp after a decimal point.

TAR_MTIME

Time of last modification.

TAR_CTIME

Time of last status change.

TAR_SIZE

Size of the file.

TAR_UID

UID of the file owner.

TAR_GID

GID of the file owner.

In addition to these variables, TAR_VERSION contains the GNU tar version number.

If command exits with a non-0 status, tar will print an error message similar to the following:

     tar: 2345: Child returned status 1

Here, ‘2345’ is the PID of the finished process.

If this behavior is not wanted, use --ignore-command-error:

--ignore-command-error

Ignore exit codes of subprocesses. Notice that if the program exits on signal or otherwise terminates abnormally, the error message will be printed even if this option is used.

--no-ignore-command-error

Cancel the effect of any previous --ignore-command-error option. This option is useful if you have set --ignore-command-error in TAR_OPTIONS (see TAR_OPTIONS) and wish to temporarily cancel it.