NAME¶
pax —
read and write file archives and
copy directory hierarchies
SYNOPSIS¶
pax |
[-0cdJjnOvz]
[-E limit]
[-f archive]
[-G group]
[-s replstr]
[-T range]
[-U user]
[pattern ...] |
pax |
-r
[-0cDdiJjknOuvYZz]
[-E limit]
[-f archive]
[-G group]
[-M flag]
[-o options]
[-p string]
[-s replstr]
[-T range]
[-U user]
[pattern ...] |
pax |
-w
[-0adHiJjLOPtuvXz]
[-B bytes]
[-b blocksize]
[-f archive]
[-G group]
[-M flag]
[-o options]
[-s replstr]
[-T range]
[-U user]
[-x format]
[file ...] |
pax |
-rw
[-0DdHiJjkLlnOPtuvXYZ]
[-G group]
[-p string]
[-s replstr]
[-T range]
[-U user]
[file ...] directory |
DESCRIPTION¶
pax will read, write, and list the members of an archive file
and will copy directory hierarchies.
pax operation is
independent of the specific archive format and supports a wide variety of
different archive formats. A list of supported archive formats can be found
under the description of the
-x option.
The presence of the
-r and the
-w options
specifies which of the following functional modes
pax will
operate under:
list,
read,
write, and
copy.
- <none>
- List. pax will write to
standard output a table of contents of the members of the archive file
read from standard input, whose pathnames match the specified
pattern arguments. The table of contents contains
one filename per line and is written using single line buffering.
- -r
- Read. pax extracts the
members of the archive file read from the standard input, with pathnames
matching the specified pattern arguments. The
archive format and blocking is automatically determined on input. When an
extracted file is a directory, the entire file hierarchy rooted at that
directory is extracted. All extracted files are created relative to the
current file hierarchy. The setting of ownership, access and modification
times, and file mode of the extracted files are discussed in more detail
under the -p option.
- -w
- Write. pax writes an
archive containing the file operands to standard
output using the specified archive format. When no
file operands are specified, a list of files to copy
with one per line is read from standard input. When a
file operand is also a directory, the entire file
hierarchy rooted at that directory will be included.
- -rw
- Copy. pax copies the
file operands to the destination
directory. When no file
operands are specified, a list of files to copy with one per line is read
from the standard input. When a file operand is also
a directory the entire file hierarchy rooted at that directory will be
included. The effect of the copy is as if the copied
files were written to an archive file and then subsequently extracted,
except that there may be hard links between the original and the copied
files (see the -l option below).
Warning: The destination directory
must not be one of the file operands or a member of
a file hierarchy rooted at one of the file operands.
The result of a copy under these conditions is
unpredictable.
While processing a damaged archive during a
read or
list operation,
pax will attempt to
recover from media defects and will search through the archive to locate and
process the largest number of archive members possible (see the
-E option for more details on error handling).
The
directory operand specifies a destination directory
pathname. If the
directory operand does not exist, or it
is not writable by the user, or it is not of type directory,
pax will exit with a non-zero exit status.
The
pattern operand is used to select one or more
pathnames of archive members. Archive members are selected using the pattern
matching notation described by
glob(3). When the
pattern operand is not supplied, all members of the
archive will be selected. When a
pattern matches a
directory, the entire file hierarchy rooted at that directory will be
selected. When a
pattern operand does not select at
least one archive member,
pax will write these
pattern operands in a diagnostic message to standard
error and then exit with a non-zero exit status.
The
file operand specifies the pathname of a file to be
copied or archived. When a
file operand does not select
at least one archive member,
pax will write these
file operand pathnames in a diagnostic message to
standard error and then exit with a non-zero exit status.
The options are as follows:
- -0
- Use the NUL (‘
\0
’)
character as a pathname terminator, instead of newline
(‘\n
’). This applies only to the
pathnames read from standard input in the write and copy modes, and to the
pathnames written to standard output in list mode. This option is expected
to be used in concert with the -print0 function in
find(1) or the -0 flag in
xargs(1).
- -a
- Append the given file operands to the
end of an archive that was previously written. If an archive format is not
specified with a -x option, the format currently being
used in the archive will be selected. Any attempt to append to an archive
in a format different from the format already used in the archive will
cause pax to exit immediately with a non-zero exit
status. The blocking size used in the archive volume where writing starts
will continue to be used for the remainder of that archive volume.
Warning: Many storage devices are not able to support the
operations necessary to perform an append operation. Any attempt to append
to an archive stored on such a device may damage the archive or have other
unpredictable results. Tape drives in particular are more likely to not
support an append operation. An archive stored in a regular file system
file or on a disk device will usually support an append operation.
- -B
bytes
- Limit the number of bytes written to a single archive
volume to bytes. The bytes
limit can end with ‘
m
’,
‘k
’, or
‘b
’ to specify multiplication by
1048576 (1M), 1024 (1K) or 512, respectively. A pair of
bytes limits can be separated by
‘x
’ to indicate a product.
Warning: Only use this option when writing an archive to a
device which supports an end of file read condition based on last (or
largest) write offset (such as a regular file or a tape drive). The use of
this option with a floppy or hard disk is not recommended.
- -b
blocksize
- When writing an archive, block the output
at a positive decimal integer number of bytes per write to the archive
file. The blocksize must be a multiple of 512 bytes
with a maximum of 64512 bytes. Archive block sizes larger than 32256 bytes
violate the POSIX standard and will not be portable to all systems. A
blocksize can end with
‘
k
’ or
‘b
’ to specify multiplication by 1024
(1K) or 512, respectively. A pair of blocksizes can
be separated by ‘x
’ to indicate a
product. A specific archive device may impose additional restrictions on
the size of blocking it will support. When blocking is not specified, the
default blocksize is dependent on the specific
archive format being used (see the -x option).
- -c
- Match all file or archive members except
those specified by the pattern and
file operands.
- -D
- This option is the same as the -u option,
except that the file inode change time is checked instead of the file
modification time. The file inode change time can be used to select files
whose inode information (e.g., UID, GID, etc.) is newer than a copy of the
file in the destination directory.
- -d
- Cause files of type directory being copied or archived, or
archive members of type directory being extracted, to match only the
directory file or archive member and not the file hierarchy rooted at the
directory.
- -E
limit
- Limit the number of consecutive read faults while trying to
read a flawed archive to limit. With a positive
limit, pax will attempt to recover
from an archive read error and will continue processing starting with the
next file stored in the archive. A limit of 0 will
cause pax to stop operation after the first read error
is detected on an archive volume. A limit of
NONE
will cause pax to attempt
to recover from read errors forever. The default
limit is a small positive number of retries.
Warning: Using this option with
NONE
should be used with extreme caution as
pax may get stuck in an infinite loop on a very badly
flawed archive.
- -f
archive
- Specify archive as the pathname of
the input or output archive, overriding the default standard input (for
list and read) or standard output (for
write). A single archive may span multiple files and
different archive devices. When required, pax will
prompt for the pathname of the file or device of the next volume in the
archive.
- -G
group
- Select a file based on its group
name, or when starting with a #, a numeric GID. A
‘
\
’ can be used to escape the
#. Multiple -G options may be supplied
and checking stops with the first match.
- -H
- Follow only command-line symbolic links while performing a
physical file system traversal.
- -i
- Interactively rename files or archive members. For each
archive member matching a pattern operand or each
file matching a file operand, pax
will prompt to /dev/tty giving the name of the file, its
file mode, and its modification time. pax will then read
a line from /dev/tty. If this line is blank, the file or
archive member is skipped. If this line consists of a single period, the
file or archive member is processed with no modification to its name.
Otherwise, its name is replaced with the contents of the line.
pax will immediately exit with a non-zero exit status if
EOF
is encountered when reading a response or if
/dev/tty cannot be opened for reading and writing.
- -J
- Use the xz utility to compress (decompress) the archive
while writing (reading). Incompatible with -a.
- -j
- Use the bzip2 utility to compress (decompress) the archive
while writing (reading). Incompatible with -a.
- -k
- Do not overwrite existing files.
- -L
- Follow all symbolic links to perform a logical file system
traversal.
- -l
- (The lowercase letter “ell”.) Link files. In
the copy mode (-r
-w), hard links are made between the source and
destination file hierarchies whenever possible.
- -M
flag
- Configure the archive normaliser.
flag is either a numeric value compatible to
strtonum(3) which is directly stored in the flags word,
or one of the following values, optionally prefixed with “no-”
to turn them off:
- inodes
- 0x0001: Serialise inodes, zero device info.
(cpio, sv4cpio, sv4crc)
- links
- 0x0002: Store content of hard links only once.
(cpio, sv4cpio, sv4crc)
- mtime
- 0x0004: Zero out the file modification time.
(ar, cpio, sv4cpio, sv4crc, ustar)
- uidgid
- 0x0008: Set owner to 0:0 (root:wheel).
(ar, cpio, sv4cpio, sv4crc, ustar)
- verb
- 0x0010: Debug this option.
- debug
- 0x0020: Debug file header storage.
- lncp
- 0x0040: Extract hard links by copy if link fails.
- numid
- 0x0080: Use only numeric uid and gid values.
(ustar)
- gslash
- 0x0100: Append a slash after directory names.
(ustar)
- set
- 0x0003: Keep ownership and mtime intact.
- dist
- 0x008B: Clean everything except mtime.
- norm
- 0x008F: Clean everything.
- root
- 0x0089: Clean owner and device information.
This option is only implemented for the ar, cpio, sv4cpio, sv4crc, and ustar
file format writing routines.
TODO: The pax frontend should be using the
-o option for handling this feature instead.
- -n
- Select the first archive member that matches each
pattern operand. No more than one archive member is
matched for each pattern. When members of type
directory are matched, the file hierarchy rooted at that directory is also
matched (unless -d is also specified).
- -O
- Force the archive to be one volume. If a volume ends
prematurely, pax will not prompt for a new volume. This
option can be useful for automated tasks where error recovery cannot be
performed by a human.
- -o
options
- Information to modify the algorithm for extracting or
writing archive files which is specific to the archive format specified by
-x. In general, options take the
form: name=value.
The following options are available for the old BSD
tar format:
- nodir
-
- write_opt=nodir
- When writing archives, omit the storage of
directories.
- -P
- Do not follow symbolic links, perform a physical file
system traversal. This is the default mode.
- -p
string
- Specify one or more file characteristic options
(privileges). The string option-argument is a string
specifying file characteristics to be retained or discarded on extraction.
The string consists of the specification characters a,
e, m, o, and
p. Multiple characteristics can be concatenated within
the same string and multiple -p options can be
specified. The meanings of the specification characters are as follows:
- a
- Do not preserve file access times. By default, file
access times are preserved whenever possible.
- e
- “Preserve everything”, the user ID, group
ID, file mode bits, file access time, and file modification time. This
is intended to be used by root, someone with all the
appropriate privileges, in order to preserve all aspects of the files
as they are recorded in the archive. The e flag is
the sum of the o and p flags.
- m
- Do not preserve file modification times. By default,
file modification times are preserved whenever possible.
- o
- Preserve the user ID and group ID.
- p
- “Preserve” the file mode bits. This is
intended to be used by a user with regular
privileges who wants to preserve all aspects of the file other than
the ownership. The file times are preserved by default, but two other
flags are offered to disable this and use the time of extraction
instead.
In the preceding list, ‘preserve’ indicates that an attribute
stored in the archive is given to the extracted file, subject to the
permissions of the invoking process. Otherwise the attribute of the
extracted file is determined as part of the normal file creation action.
If neither the e nor the o
specification character is specified, or the user ID and group ID are not
preserved for any reason, pax will not set the
S_ISUID
(setuid) and
S_ISGID
(setgid) bits of the
file mode. If the preservation of any of these items fails for any reason,
pax will write a diagnostic message to standard error.
Failure to preserve these items will affect the final exit status, but
will not cause the extracted file to be deleted. If the file
characteristic letters in any of the string option-arguments are
duplicated or conflict with each other, the one(s) given last will take
precedence. For example, if -p eme
is specified, file modification times are still preserved.
- -r
- Read an archive file from standard input and extract the
specified file operands. If any intermediate
directories are needed in order to extract an archive member, these
directories will be created as if mkdir(2) was called
with the bitwise inclusive OR of
S_IRWXU
,
S_IRWXG
, and S_IRWXO
as
the mode argument. When the selected archive format supports the
specification of linked files and these files cannot be linked while the
archive is being extracted, pax will write a diagnostic
message to standard error and exit with a non-zero exit status at the
completion of operation.
- -s
replstr
- Modify the archive member names according to the
substitution expression replstr, using the syntax of
the ed(1) utility regular expressions.
file or pattern arguments may
be given to restrict the list of archive members to those specified.
The format of these regular expressions is:
/old/new/[gp]
As in ed(1), old is a basic regular
expression (see re_format(7)) and
new can contain an ampersand
(‘&
’),
‘\n
’ (where
n is a digit) back-references, or subexpression
matching. The old string may also contain newline
characters. Any non-null character can be used as a delimiter
(‘/
’ is shown here). Multiple
-s expressions can be specified. The expressions are
applied in the order they are specified on the command line, terminating
with the first successful substitution.
The optional trailing g continues to apply the
substitution expression to the pathname substring, which starts with the
first character following the end of the last successful substitution. The
first unsuccessful substitution stops the operation of the
g option. The optional trailing p will
cause the final result of a successful substitution to be written to
standard error in the following format:
original-pathname
>> new-pathname
File or archive member names that substitute to the empty string are not
selected and will be skipped.
- -T
range
- Allow files to be selected based on a file modification or
inode change time falling within the specified time range. The range has
the format:
[from_date][,to_date][/[c][m]]
The dates specified by from_date to
to_date are inclusive. If only a
from_date is supplied, all files with a modification
or inode change time equal to or younger are selected. If only a
to_date is supplied, all files with a modification
or inode change time equal to or older will be selected. When the
from_date is equal to the
to_date, only files with a modification or inode
change time of exactly that time will be selected.
When pax is in the write or
copy mode, the optional trailing field
[c][m]
can be used to determine which file time (inode change, file modification
or both) are used in the comparison. If neither is specified, the default
is to use file modification time only. The m specifies
the comparison of file modification time (the time when the file was last
written). The c specifies the comparison of inode change
time (the time when the file inode was last changed; e.g., a change of
owner, group, mode, etc). When c and m
are both specified, then the modification and inode change times are both
compared.
The inode change time comparison is useful in selecting files whose
attributes were recently changed or selecting files which were recently
created and had their modification time reset to an older time (as what
happens when a file is extracted from an archive and the modification time
is preserved). Time comparisons using both file times is useful when
pax is used to create a time based incremental archive
(only files that were changed during a specified time range will be
archived).
A time range is made up of six different fields and each field must contain
two digits. The format is:
[[[[[cc]yy]mm]dd]HH]MM[.SS]
Where cc is the first two digits of the year (the
century), yy is the last two digits of the year, the
first mm is the month (from 01 to 12),
dd is the day of the month (from 01 to 31),
HH is the hour of the day (from 00 to 23),
MM is the minute (from 00 to 59), and
SS is the seconds (from 00 to 59). The minute field
MM is required, while the other fields are optional
and must be added in the following order: HH,
dd, mm,
yy, cc.
The SS field may be added independently of the other
fields. Time ranges are relative to the current time, so -T
1234/cm would select all files with a modification or inode change
time of 12:34 PM today or later. Multiple -T time range
can be supplied and checking stops with the first match.
- -t
- Reset the access times of any file or directory read or
accessed by pax to be the same as they were before being
read or accessed by pax.
- -U
user
- Select a file based on its user name,
or when starting with a #, a numeric UID. A
‘
\
’ can be used to escape the
#. Multiple -U options may be supplied
and checking stops with the first match.
- -u
- Ignore files that are older (having a less recent file
modification time) than a pre-existing file or archive member with the
same name. During read, an archive member with the same
name as a file in the file system will be extracted if the archive member
is newer than the file. During write, a file system
member with the same name as an archive member will be written to the
archive if it is newer than the archive member. During
copy, the file in the destination hierarchy is replaced
by the file in the source hierarchy or by a link to the file in the source
hierarchy if the file in the source hierarchy is newer.
- -v
- During a list operation, produce a
verbose table of contents using the format of the ls(1)
utility with the -l option. For pathnames representing a
hard link to a previous member of the archive, the output has the format:
ls -l listing
==
link-name
For pathnames representing a symbolic link, the output has the format:
ls -l listing
=>
link-name
Where ls -l listing is the output format specified by the
ls(1) utility when used with the -l
option. Otherwise for all the other operational modes
(read, write,
and copy), pathnames are written
and flushed to standard error without a trailing newline as soon as
processing begins on that file or archive member. The trailing newline is
not buffered and is written only after the file has been read or
written.
- -w
- Write files to the standard output in the specified archive
format. When no file operands are specified,
standard input is read for a list of pathnames with one per line without
any leading or trailing ⟨blanks⟩.
- -X
- When traversing the file hierarchy specified by a pathname,
do not descend into directories that have a different device ID. See the
st_dev
field as described in
stat(2) for more information about device IDs.
- -x
format
- Specify the output archive format, with the default format
being ustar. pax currently supports
the following formats:
- ar
- The Unix Archiver library format. This format matches
APT repositories and the BSD ar(1) specification,
not GNU binutils (which can however read them) or SYSV systems. See
ar(5) on some operating systems for more
information.
- bcpio
- The old binary cpio format. The default blocksize for
this format is 5120 bytes. This format is not very portable and should
not be used when other formats are available. Inode and device
information about a file (used for detecting file hard links by this
format), which may be truncated by this format, is detected by
pax and is repaired.
- cpio
- The extended cpio interchange format specified in the
IEEE Std 1003.2 (“POSIX.2”)
standard. The default blocksize for this format is 5120 bytes. Inode
and device information about a file (used for detecting file hard
links by this format), which may be truncated by this format, is
detected by pax and is repaired.
- sv4cpio
- The System V release 4 cpio. The default blocksize for
this format is 5120 bytes. Inode and device information about a file
(used for detecting file hard links by this format), which may be
truncated by this format, is detected by pax and is
repaired.
- sv4crc
- The System V release 4 cpio with file CRC checksums.
The default blocksize for this format is 5120 bytes. Inode and device
information about a file (used for detecting file hard links by this
format), which may be truncated by this format, is detected by
pax and is repaired.
- tar
- The old BSD tar format as found
in 4.3BSD. The default blocksize for this
format is 10240 bytes. Pathnames stored by this format must be 100
characters or less in length. Only regular files,
hard links, soft links, and
directories will be archived (other file system
types are not supported). For backwards compatibility with even older
tar formats, a -o option can be used when writing an
archive to omit the storage of directories. This option takes the
form:
-o
write_opt=nodir
- ustar
- The extended tar interchange format specified in the
IEEE Std 1003.2 (“POSIX.2”)
standard. The default blocksize for this format is 10240 bytes.
Filenames stored by this format must be 100 characters or less in
length; the total pathname must be 256 characters or less.
pax will detect and report any file that it is unable to
store or extract as the result of any specific archive format
restrictions. The individual archive formats may impose additional
restrictions on use. Typical archive format restrictions include (but are
not limited to): file pathname length, file size, link pathname length,
and the type of the file.
- -Y
- This option is the same as the -D option,
except that the inode change time is checked using the pathname created
after all the file name modifications have completed.
- -Z
- This option is the same as the -u option,
except that the modification time is checked using the pathname created
after all the file name modifications have completed.
- -z
- Use the gzip(1) utility to compress
(decompress) the archive while writing (reading). Incompatible with
-a.
The options that operate on the names of files or archive members
(
-c,
-i,
-n,
-s,
-u,
-v,
-D,
-G,
-T,
-U,
-Y, and
-Z) interact
as follows.
When extracting files during a
read operation, archive members
are ‘selected’, based only on the user specified pattern operands
as modified by the
-c,
-n,
-u,
-D,
-G,
-T,
-U options. Then any
-s and
-i options will modify in that
order, the names of these selected files. Then the
-Y and
-Z options will be applied based on the final pathname.
Finally, the
-v option will write the names resulting from
these modifications.
When archiving files during a
write operation, or copying
files during a
copy operation, archive members are
‘selected’, based only on the user specified pathnames as modified
by the
-n,
-u,
-D,
-G,
-T, and
-U options
(the
-D option only applies during a copy operation). Then
any
-s and
-i options will modify in that
order, the names of these selected files. Then during a
copy
operation the
-Y and the
-Z options will
be applied based on the final pathname. Finally, the
-v
option will write the names resulting from these modifications.
When one or both of the
-u or
-D options are
specified along with the
-n option, a file is not considered
selected unless it is newer than the file to which it is compared.
ENVIRONMENT¶
TMPDIR
- Path in which to store temporary files.
EXIT STATUS¶
The
pax utility exits with one of the following values:
- 0
- All files were processed successfully.
- 1
- An error occurred.
EXAMPLES¶
Copy the contents of the current directory to the device
/dev/rst0:
$ pax -w -f /dev/rst0 .
Give the verbose table of contents for an archive stored in
filename:
$ pax -v -f filename
This sequence of commands will copy the entire
olddir
directory hierarchy to
newdir:
$ mkdir newdir
$ cd olddir
$ pax -rw . ../newdir
Extract files from the archive
a.pax. Files rooted in
/usr are extracted relative to the current working
directory; all other files are extracted to their unmodified path.
$ pax -r -s ',^/usr/,,' -f a.pax
This can be used to interactively select the files to copy from the current
directory to
dest_dir:
$ pax -rw -i . dest_dir
Extract all files from the archive
a.pax which are owned by
root with group
bin and preserve all file
permissions:
$ pax -r -pe -U root -G bin -f
a.pax
Update (and list) only those files in the destination directory
/backup which are older (less recent inode change or file
modification times) than files with the same name found in the source file
tree
home:
$ pax -r -w -v -Y -Z home /backup
DIAGNOSTICS¶
Whenever
pax cannot create a file or a link when reading an
archive or cannot find a file when writing an archive, or cannot preserve the
user ID, group ID, or file mode when the
-p option is
specified, a diagnostic message is written to standard error and a non-zero
exit status will be returned, but processing will continue. In the case where
pax cannot create a link to a file, unless
-M lncp is given,
pax will not create a second copy of the file.
If the extraction of a file from an archive is prematurely terminated by a
signal or error,
pax may have only partially extracted a
file the user wanted. Additionally, the file modes of extracted files and
directories may have incorrect file bits, and the modification and access
times may be wrong.
If the creation of an archive is prematurely terminated by a signal or error,
pax may have only partially created the archive, which may
violate the specific archive format specification.
If while doing a
copy,
pax detects a file is
about to overwrite itself, the file is not copied, a diagnostic message is
written to standard error and when
pax completes it will
exit with a non-zero exit status.
SEE ALSO¶
ar(1),
cpio(1),
deb(5),
paxcpio(1),
paxtar(1),
tar(1)
STANDARDS¶
The
pax utility is compliant with the IEEE Std 1003.1-2008
(“POSIX”) specification.
The flags
-0BDEGHJjLMOPTUYZz, the archive formats
ar,
bcpio,
sv4cpio,
sv4crc,
tar, and the flawed archive
handling during
list and
read operations
are extensions to that specification.
AUTHORS¶
Keith Muller at the University of California, San Diego.
MirOS extensions by
Thorsten Glaser
⟨tg@mirbsd.org⟩.
BUGS¶
The
pax file format is not yet supported.