| ||pax - portable archive interchange
| ||pax [-cdnv] [-f archive] [-s replstr] ... [pattern ...]
| ||pax -r [-cdiknuv] [-f archive] [-o options ...] [-p string] ... [-s replstr] ... [pattern ...]
| ||pax -w [-dituvX@] [-b blocksize] [-a] [-f archive] [-o options] ... [-s replstr] ... [-x format] [file ...]
| ||pax -r -w [-diklntuvX@] [-p string] ... [-s replstr] ... [file ...] directory
The pax command reads, writes and writes lists of the members of archive files and copy directory hierarchies. A variety of archive formats are supported. See the -x format option.
Modes of Operations
The action to be taken depends on the presence of the -r and -w options. The four combinations of -r and -w are referred to as the four modes of operation: list, read, write, and copy modes, corresponding respectively to the four forms shown in the SYNOPSIS.
- In list mode (when neither -r nor -w are specified), pax writes the names of the members of the archive file read from the standard input, with path names matching the specified patterns, to standard output. If a named file has extended attributes, the extended attributes are also listed. If a named file is of type directory, the file hierarchy rooted at that file will be written out as well.
- In read mode (when -r is specified, but -w is not), pax extracts the members of the archive file read from the standard input, with path names matching the specified patterns. If an extracted file is of type directory, the file hierarchy rooted at that file will be extracted as well. The extracted files is created relative to the current file hierarchy.
The ownership, access and modification times, and file mode of the restored files are discussed under the -p option.
- In write mode (when -w is specified, but -r is not), pax writes the contents of the file operands to the standard output in an archive format. If no file operands are specified, a list of files to copy, one per line, will be read from the standard input. A file of type directory will include all of the files in the file hierarchy rooted at the file.
- In copy mode (when both -r and -w are specified), pax copies the file operands to the destination directory.
If no file operands are specified, a list of files to copy, one per line, will be read from the standard input. A file of type directory will include all of the files in the file hierarchy rooted at the file.
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. If the destination directory is a subdirectory of one of the files to be copied, the results are unspecified. It is an error if directory does not exist, is not writable by the user, or is not a directory.
In read or copy modes, if intermediate directories are necessary to extract an archive member, pax will perform actions equivalent to the mkdir(2) function, called with the following arguments:
- the intermediate directory used as the path argument
- the octal value of 777 or rwx (read, write, and execute permissions) as the mode argument (see chmod(1)).
If any specified pattern or file operands are not matched by at least one file or archive member, pax will write a diagnostic message to standard error for each one that did not match and exit with a non-zero exit status.
The supported archive formats are automatically detected on input. The default output archive format is tar(1).
If the selected archive format supports the specification of linked files, it is an error if these files cannot be linked when the archive is extracted. Any of the various names in the archive that represent a file can be used to select the file for extraction.
The following options are supported:
- Reads an archive file from standard input.
- Writes files to the standard output in the specified archive format.
- Appends files to the end of the archive. This option will not work for some archive devices, such as 1/4-inch streaming tapes and 8mm tapes.
- -b blocksize
- Blocks the output at a positive decimal integer number of bytes per write to the archive file. Devices and archive formats may impose restrictions on blocking. Blocking is automatically determined on input. Portable applications must not specify a blocksize value larger than 32256. Default blocking when creating archives depends on the archive format. See
the -x option below.
- Matches all file or archive members except those specified by the pattern or file operands.
- Causes files of type directory being copied or archived or archive members of type directory being extracted to match only the file or archive member itself and not the file hierarchy rooted at the file.
- -f archive
- Specifies the path name of the input or output archive, overriding the default standard input (in list or read modes) or standard output (write mode).
- Interactively renames files or archive members. For each archive member matching a pattern operand or file matching a file operand, a prompt will be written to the file /dev/tty. The prompt will contain the name of the file or archive member. A line will then be read from /dev/tty. If this line is blank, the file or archive member will be skipped.
If this line consists of a single period, the file or archive member will be processed with no modification to its name. Otherwise, its name will be replaced with the contents of the line. The pax command will immediately exit with a non-zero exit status if end-of-file is encountered when reading a response or if /dev/tty cannot be opened for reading and writing.
- Prevents the overwriting of existing files.
- Links files. In copy mode, hard links will be made between the source and destination file hierarchies whenever possible.
- Selects the first archive member that matches each pattern operand. No more than one archive member will be matched for each pattern, although members of type directory will still match the file hierarchy rooted at that file.
- -o options
- Reserved for special format-specific options.
- -p string
- Specifies one or more file characteristic options (privileges). The string option-argument must be 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 meaning of the specification characters are as follows:
- Does not preserve file access times.
- Preserves the user ID, group ID, file mode bits, access time, and modification time.
- Does not preserve file modification times.
- Preserves the user ID and group ID.
- Preserves the file mode bits. Other, implementation-dependent file-mode attributes may be preserved.
In the preceding list, ``preserve'' indicates that an attribute stored in the archive will be given to the extracted file, subject to the permissions of the invoking process. Otherwise, the attribute will be 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 setuid and 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 file-characteristic letters in any of the string option-arguments are duplicated or conflict with each other, the ones given last will take precedence. For example, if -p eme is specified, file modification times will be preserved.
- -s replstr
- Modifies file or archive member names named by pattern or file operands according to the substitution expression replstr, which is based on the ed(1) s (substitution) command, using the regular expression
syntax on the regex(5) manual page. The concepts of ``address'' and ``line'' are meaningless in the context of the pax command, and must not be supplied. The format is:
where, as in ed, old is a basic regular expression and new can contain an ampersand (&) or a \n backreference, where n is a digit. The old string also is permitted to contain newline characters.
Any non-null character can be used as a delimiter ( / shown here). Multiple -s expressions can be specified; the expressions will be applied in the order specified, terminating with the first successful substitution. The optional trailing g is as defined in the ed command. The optional trailing p causes successful substitutions to be written to standard error. File or archive member names that substitute
to the empty string are ignored when reading and writing archives.
- Causes the access times of the archived files to be the same as they were before being read by pax.
- Ignores files that are older (having a less recent file modification time) than a pre-existing file or archive member with the same name.
- read mode
- 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.
- write mode
- An archive file member with the same name as a file in the file system will be superseded if the file is newer than the archive member.
- copy mode
- The file in the destination hierarchy will be 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.
- In list mode, produces a verbose table of contents (see Standard Output). Otherwise, writes archive member path names and extended attributes to standard error (see Standard Error).
- -x format
- Specifies the output archive format. The pax command recognizes the following formats:
- The extended cpio(1) interchange format. See the IEEE 1003.1(1990) specifications. The default blocksize for this format for character special archive files is 5120. Implementations support all blocksize values less than or equal to 32256 that are multiples of 512.
This archive format allows files with UIDs and GIDs up to 262143 to be stored in the archive. Files with UIDs and GIDs greater than this value will be archived with the UID and GID of 60001.
- The extended tar(1) interchange format. See the IEEE 1003.1(1990) specifications. The default blocksize for this format for character special archive files is 10240. Implementations support all blocksize values less than or equal to 32256
that are multiples of 512.
Any attempt to append to an archive file in a format different from the existing archive format will cause pax to exit immediately with a non-zero exit status.
This archive format allows files with UIDs and GIDs up to 2097151 to be stored in the archive. Files with UIDs and GIDs greater than this value will be archived with the UID and GID of 60001.
- Similar to ustar. Will also allow archiving and extracting files whose size is greater than 8GB; whose UID, GID, devmajor, or devminor values are greater than 2097151; whose path (including filename) is greater than 255 characters; or whose linkname is greater than 100 characters. This option should not be used if the
archive is to be extracted by an archiver that cannot handle the larger values.
- When traversing the file hierarchy specified by a path name, pax will not descend into directories that have a different device ID (st_dev, see stat(2)).
- When traversing the file hierarchy specified by a path name, pax will descend into the attribute directory for any file with extended attributes. Extended attributes go into the archive as special files. When this flag is used during file extraction, any extended attributes associated with a file being extracted are also extracted. Extended attribute files can only be extracted from an archive as part of a normal file
extract. Attempts to explicitly extract attribute records are ignored.
The options that operate on the names of files or archive members (-c, -i, -n, -s, -u and -v) interact as follows. In read mode, the archive members are selected based on the user-specified pattern operands as modified by the -c, -n and -u options. Then, any -s and -i options will
modify, in that order, the names of the selected files. The -v option will write names resulting from these modifications.
In write mode, the files are selected based on the user-specified path names as modified by the -n and -u options. Then, any -s and -i options will, in that order, modify the names of these selected files. The -v option will write names resulting from these modifications.
If both the -u and -n options are specified, pax does not consider a file selected unless it is newer than the file to which it is compared.
The following operands are supported:
- The destination directory path name for copy mode.
- A path name of a file to be copied or archived.
- A pattern matching one or more path names of archive members. A pattern must conform to the pattern matching notation found on the fnmatch(5) manual page. The default, if no pattern is specified, is to select all members in the archive.
In write mode, if -f is not specified, the standard output will be the archive formatted according to cpio or ustar. (See -x format.)
In list mode, the table of contents of the selected archive members will be written to standard output using the following format:
If the -v option is specified in list mode, the table of contents of the selected archive members will be written to standard output using the following formats:
For path names representing hard links to previous members of the archive:
"%s==%s\n" <ls -l listing>, linkname
For all other path names:
<pathname> "%s\n" <ls -l listing>
where <ls -l listing> is the format specified by the ls command with the -l option. When writing path names in this format, it is unspecified what is written for fields for which the underlying archive format does not have the correct information, although the correct number of blank-character-separated fields will be written.
In list mode, standard output will not be buffered more than a line at a time.
If -v is specified in read, write or copy modes, pax will write the path names it processes to the standard error output using the following format:
These path names will be written as soon as processing is begun on the file or archive member, and will be flushed to standard error. The trailing newline character, which will not be buffered, will be written when the file has been read or written.
If the -s option is specified, and the replacement string has a trailing p, substitutions will be written to standard error in the following format:
"%s>>%s\n" <original pathname>, <new pathname>
In all operating modes of pax, optional messages of unspecified format concerning the input archive format and volume number, the number of files, blocks, volumes and media parts as well as other diagnostic messages may be written to standard error.
In all formats, for both standard output and standard error, it is unspecified how non-printable characters in path names or linknames are written.
If 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 will be 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, pax
will not, by default, 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 the file or (if the -n option was not specified) may have extracted a file of the same name as that specified by the user, but which is not the file the user wanted. Additionally, the file modes of extracted directories may have additional bits from the read, write, execute mask set as well as incorrect modification and access times.
The -p (privileges) option was invented to reconcile differences between historical tar(1) and cpio(1) implementations. In particular, the two utilities use -m in diametrically opposed ways. The -p option also provides a consistent
means of extending the ways in which future file attributes can be addressed, such as for enhanced security systems or high-performance files. Although it may seem complex, there are really two modes that will be most commonly used:
- -p e
- ``Preserve everything''. This would be used by the historical superuser, someone with all the appropriate privileges, to preserve all aspects of the files as they are recorded in the archive. The e flag is the sum of o and p, and other implementation-dependent attributes.
- -p p
- ``Preserve'' the file mode bits. This would be used by the user with regular privileges who wished to preserve aspects of the file other than the ownership. The file times are preserved by default, but two other flags are offered to disable these and use the time of extraction.
See largefile(5) for the description of the behavior of pax when encountering files greater than or equal to 2 Gbyte ( 231 bytes).
| ||Example 1. Copying the contents of the current directory
Example 2. Copying the directory hierarchy
The following command:
example% pax -w -f /dev/rmt/1m .
copies the contents of the current directory to tape drive 1, medium density. (This assumes historical System V device naming procedures. The historical BSD device name would be /dev/rmt9).
Example 3. Reading an archive extracted relative to the current directory
The following commands:
example% mkdir newdir
example% pax -rw olddir newdir
copy the olddir directory hierarchy to newdir.
The following command:
example% pax -r -s ',^//*usr//*,,' -f a.pax
reads the archive a.pax, with all files rooted in /usr in the archive extracted relative to the current directory.
See environ(5) for descriptions of the following environment variables that affect the execution of pax: LC_CTYPE, LC_MESSAGES, LC_TIME, and NLSPATH.
- Determine the locale for the behaviour of ranges, equivalence classes, and multi-character collating elements used in the pattern matching expressions for the pattern operand, the basic regular expression for the -s option, and the extended regular expression defined for the yesexpr locale keyword in the LC_MESSAGES category.
The following exit values are returned:
- All files were processed successfully.
- An error occurred.
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE
chmod(1), cpio(1), ed(1), tar(1), mkdir(2), stat(2), attributes(5), environ(5), fnmatch(5), fsattr(5), largefile(5), regex(5)