.hy 0

.nr HY 0

\fBlz4, unlz4, lz4cat\fR \- Compress or decompress .lz4 files

.TP 5

.PP

.B unlz4

is equivalent to

.BR "lz4 \-d"

.br

.B lz4cat

is equivalent to

.BR "lz4 \-dc"

.br

.PP

When writing scripts that need to decompress files,

it is recommended to always use the name

.B lz4

with appropriate arguments

.RB ( "lz4 \-d"

or

.BR "lz4 \-dc" )

instead of the names

.B unlz4

and

.BR lz4cat .

.PP

\fBlz4\fR is an extremely fast lossless compression algorithm,

based on \fBbyte-aligned LZ77\fR family of compression scheme.

\fBlz4\fR offers compression speeds of 400 MB/s per core, linearly scalable with multi-core CPUs.

It features an extremely fast decoder, with speed in multiple GB/s per core,

typically reaching RAM speed limit on multi-core systems.

.B lz4

supports a command line syntax similar to

.BR gzip (1).

The native file format is the

.B .lz4

format.

It is possible to concatenate

.B .lz4

files as is.

.B lz4

will decompress such files as if they were a single

.B .lz4

file. For example:

lz4 file1 > foo.lz4

lz4 file2 >> foo.lz4

then

lz4cat foo.lz4

is equivalent to :

cat file1 file2

.PP

In some cases, some options can be expressed using short command

.B "-x"

or long command

.B "--long-word" .

Short commands can be concatenated together. For example,

.B "-d -c"

is equivalent to

.B "-dc" .

Long commands cannot be concatenated.

They must be clearly separated by a space.

When multiple contradictory commands are issued on a same command line,

only the latest one will be applied.

.TP

Compress.

This is the default operation mode

when no operation mode option is specified ,

no other operation mode is implied from the command name

(for example,

.B unlz4

implies

.B \-\-decompress ),

nor from the input file name

(for example, a file extension

.B .lz4

implies

.B \-\-decompress

by default).

.B -z

can also be used to force compression of an already compressed

.B .lz4

file.

.TP

Decompress.

.B --decompress

is also the default operation when the input filename has an

.B .lz4

extensionq

.TP

Test the integrity of compressed

.B .lz4

files.

The decompressed data is discarded.

No files are created nor removed.

.TP

fast compression (default)

.TP

high compression

.TP

This option has several effects:

.RS

.IP \(bu 3

If the target file already exists,

overwrite it without prompting.

.IP \(bu 3

When used with

.B \-\-decompress

and

.B lz4

cannot recognize the type of the source file,

copy the source file as is to standard output.

This allows

.B lz4cat

.B \-\-force

to be used like

.BR cat (1)

for files that have not been compressed with

.BR lz4 .

.RE

.TP

force write to standard output, even if it is the console

.TP

Multiple file names.

By default, the second filename is used as the output filename for the compressed file.

With

.B -m

, you can specify any number of input filenames. Each of them will be compressed

independently, and the resulting name of the compressed file will be

.B filename.lz4

.TP

block size [4-7](default : 7)

B4= 64KB ; B5= 256KB ; B6= 1MB ; B7= 4MB

.TP

block dependency (improve compression ratio)

.TP

select frame checksum (default:enabled)

.TP

header includes original size (default:not present)

Note : this option can only be activated when the original size can be determined,

hence for a file. It won't work with unknown source size, such as stdin or pipe.

.TP

sparse mode support (default:enabled on file, disabled on stdout)

.TP

use Legacy format (useful for Linux Kernel compression)

.TP

verbose mode

.TP

suppress warnings; specify twice to suppress errors too

.TP

display help/long help and exit

.TP

display Version number and exit

.TP

Don't delete source file.

This is default behavior anyway, so this option is just for compatibility with gzip/xz.

.TP

benchmark file(s)

.TP

iteration loops [1-9](default : 3), benchmark mode only

Report bugs at: https://github.com/Cyan4973/lz4

Yann Collet