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.TH PACK 1 "Feb 5, 2020"
.SH NAME
pack, pcat, unpack \- compress and expand files
.SH SYNOPSIS
.nf
\fBpack\fR [\fB-f/\fR] [\fB-\fR] \fIfile\fR...
.fi

.LP
.nf
\fBpcat\fR \fIfile\fR...
.fi

.LP
.nf
\fBunpack\fR [\fB-/\fR] \fIfile\fR...
.fi

.SH DESCRIPTION
.SS "pack"
The \fBpack\fR command attempts to store the specified files in a compressed
form. Wherever possible (and useful), each input file \fBfile\fR is replaced by
a packed file \fBfile\fR\fB\&.z\fR with the same access modes, access and
modified dates, and owner as those of \fBfile\fR. If \fBpack\fR is successful,
\fBfile\fR is removed.
.sp
.LP
The amount of compression obtained depends on the size of the input file and
the character frequency distribution. Because a decoding tree forms the first
part of each \fB\&.z\fR file, it is usually not worthwhile to pack files
smaller than three blocks, unless the character frequency distribution is very
skewed, which can occur with printer plots or pictures.
.sp
.LP
Typically, text files are reduced to 60-75% of their original size. Load
modules, which use a larger character set and have a more uniform distribution
of characters, show little compression, the packed versions being about 90% of
the original size.
.sp
.LP
The \fBpack\fR utility returns a value that is the number of files that it
failed to compress. If that number exceeds \fB255\fR, \fB255\fR is returned.
.sp
.LP
No packing occurs if:
.RS +4
.TP
.ie t \(bu
.el o
the file appears to be already packed
.RE
.RS +4
.TP
.ie t \(bu
.el o
the file name is too long to add the \fB\&.z\fR suffix
.RE
.RS +4
.TP
.ie t \(bu
.el o
the file has links
.RE
.RS +4
.TP
.ie t \(bu
.el o
the file is a directory
.RE
.RS +4
.TP
.ie t \(bu
.el o
the file cannot be opened
.RE
.RS +4
.TP
.ie t \(bu
.el o
the file is empty
.RE
.RS +4
.TP
.ie t \(bu
.el o
no disk storage blocks are saved by packing
.RE
.RS +4
.TP
.ie t \(bu
.el o
a file called \fBfile\fR\fB\&.z\fR already exists
.RE
.RS +4
.TP
.ie t \(bu
.el o
the \fB\&.z\fR file cannot be created
.RE
.RS +4
.TP
.ie t \(bu
.el o
an I/O error occurred during processing.
.RE
.sp
.LP
The last segment of the file name must be short enough to allow space for the
appended \fB\&.z\fR extension. Directories cannot be compressed.
.SS "pcat"
The \fBpcat\fR command does for packed files what \fBcat\fR(1) does for
ordinary files, except that \fBpcat\fR cannot be used as a filter. The
specified files are unpacked and written to the standard output.
.sp
.LP
\fBpcat\fR returns the number of files it was unable to unpack. Failure can
occur if:
.RS +4
.TP
.ie t \(bu
.el o
the file cannot be opened;
.RE
.RS +4
.TP
.ie t \(bu
.el o
the file does not appear to be the output of \fBpack\fR.
.RE
.SS "unpack"
The \fBunpack\fR command expands files created by \fBpack\fR. For each
\fBfile\fR specified in the command, a search is made for a file called
\fBfile\fR\fB\&.z\fR (or just \fBfile\fR, if \fBfile\fR ends in \fB\&.z\fR). If
this file appears to be a packed file, it is replaced by its expanded version.
The new file has the \fB\&.z\fR suffix stripped from its name, and has the same
access modes, access and modification dates, and owner as those of the packed
file.
.sp
.LP
\fBunpack\fR returns a value that is the number of files it was unable to
unpack. Failure can occur for the same reasons that it can in \fBpcat\fR, as
well as for the following:
.RS +4
.TP
.ie t \(bu
.el o
a file with the unpacked name already exists;
.RE
.RS +4
.TP
.ie t \(bu
.el o
the unpacked file cannot be created.
.RE
.SH OPTIONS
The following options are supported by \fBpack\fR:
.sp
.ne 2
.na
\fB\fB-f\fR\fR
.ad
.RS 6n
Forces packing of \fBfile\fR. This is useful for causing an entire directory to
be packed even if some of the files do not benefit. Packed files can be
restored to their original form using \fBunpack\fR or \fBpcat\fR.
.RE

.sp
.LP
The following options are supported by \fBpack\fR and \fBunpack\fR:
.sp
.ne 2
.na
\fB\fB-/\fR\fR
.ad
.RS 6n
When packing or unpacking, copies any ACL and extended system attributes
associated with the source file to the target file. If an ACL or extended
system attributes cannot be copied, the original file is retained, a diagnostic
message is written to \fBstderr\fR, and the final exit status is
\fBnon-zero\fR.
.RE

.SH OPERANDS
The following operands are supported:
.sp
.ne 2
.na
\fB\fBfile\fR\fR
.ad
.RS 8n
A path name of a file to be packed, unpacked, or pcated; \fBfile\fR can include
or omit the \fB\&.z\fR suffix.
.RE

.sp
.ne 2
.na
\fB\fB\(mi\fR\fR
.ad
.RS 8n
\fBpack\fR uses Huffman (minimum redundancy) codes on a byte-by-byte basis. If
the \fB\(mi\fR argument is used, an internal flag is set that causes the number
of times each byte is used, its relative frequency, and the code for the byte
to be printed on the standard output. Additional occurrences of \fB\(mi\fR in
place of \fBfile\fR causes the internal flag to be set and reset.
.RE

.SH USAGE
See \fBlargefile\fR(5) for the description of the behavior of \fBpack\fR,
\fBpcat\fR, and \fBunpack\fR when encountering files greater than or equal to 2
Gbyte (2^31 bytes).
.SH EXAMPLES
\fBExample 1 \fRViewing a Packed File
.sp
.LP
To view a packed file named \fBfile.z\fR use:

.sp
.LP
\fBexample%\fR \fBpcat\fR \fBfile.z\fR

.sp
.LP
or just:

.sp
.LP
\fBexample%\fR \fBpcat\fR \fBfile\fR

.LP
\fBExample 2 \fRMaking an Unpacked Copy:
.sp
.LP
To make an unpacked copy, say \fBnnn\fR, of a packed file named \fBfile.z\fR
(without destroying \fBfile.z\fR) use the command:

.sp
.LP
\fBexample%\fR \fBpcat\fR \fBfile\fR \fB>nnn\fR

.SH ENVIRONMENT VARIABLES
See \fBenviron\fR(5) for descriptions of the following environment variables
that affect the execution of \fBpack\fR, \fBpcat\fR, and \fBunpack\fR:
\fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
.SH EXIT STATUS
The following exit values are returned:
.sp
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 6n
Successful completion.
.RE

.sp
.ne 2
.na
\fB\fB>0\fR\fR
.ad
.RS 6n
An error occurred. The number of files the command failed to pack/unpack is
returned. If the number of failures exceeds \fB255\fR, then \fB255\fR is
returned.
.RE

.SH ATTRIBUTES
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
CSI	Enabled
.TE

.SH SEE ALSO
\fBcat\fR(1), \fBcompress\fR(1), \fBzcat\fR(1), \fBfgetattr\fR(3C),
\fBfsetattr\fR(3C), \fBattributes\fR(5), \fBenviron\fR(5), \fBlargefile\fR(5)