Tar/Writing-to-an-External-Program
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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. The command
may
contain command line arguments (see Running External Commands,
for more detail).
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.
Additionally, the following variables contain information about tar mode and the archive being processed:
TAR_VERSION
- GNU
tar
version number. TAR_ARCHIVE
- The name of the archive
tar
is processing. TAR_BLOCKING_FACTOR
- Current blocking factor (see section Blocking).
TAR_VOLUME
- Ordinal number of the volume
tar
is processing. TAR_FORMAT
- Format of the archive being processed. See section Controlling the Archive Format, for a complete list of archive format names.
These variables are defined prior to executing the command, so you can
pass them as arguments, if you prefer. For example, if the command
proc
takes the member name and size as its arguments, then you
could do:
$ tar -x -f archive.tar \ --to-command='proc $TAR_FILENAME $TAR_SIZE' |
Notice single quotes to prevent variable names from being expanded by
the shell when invoking tar
.
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.
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