CLI Overview

Command-line interface overview and basic usage for zstd compression tool

zstd is a fast lossless compression algorithm and data compression tool, with command line syntax similar to gzip and xz. It is based on the LZ77 family, with further FSE & huff0 entropy stages.

Key Features

• Fast compression: > 200 MB/s per core in fast modes
• Strong compression: Excellent compression ratios with configurable levels
• Fast decompression: > 500 MB/s per core across all compression settings
• Dictionary compression: Dramatically improves compression on small files
• Multi-threading support: Parallel compression with -T# option

Basic Usage

zstd [OPTIONS...] [INPUT... | -] [-o OUTPUT]

Compress a file

# Compress with default level (3)
zstd file.txt
# Output: file.txt.zst

# Compress with specific level (1-19)
zstd -5 file.txt

# Compress with maximum compression
zstd -19 file.txt

Decompress a file

# Decompress
zstd -d file.txt.zst
# Output: file.txt

# Alternative syntax
unzstd file.txt.zst

Write to standard output

# Decompress to stdout
zstd -dc file.txt.zst

# Alternative
zstdcat file.txt.zst

Common Options

Option	Description
-#	Compression level (1-19, default: 3)
-d, --decompress	Decompress files
-o OUTPUT	Write output to OUTPUT file
-k, --keep	Keep input files (default)
--rm	Remove input files after processing
-f, --force	Overwrite existing files
-c, --stdout	Write to stdout
-v, --verbose	Verbose mode
-q, --quiet	Suppress warnings
-h, --help	Display help

Differences from gzip

zstd has several behavioral differences from gzip:

• Source files are preserved by default (use --rm to remove)
• Progress notifications are shown by default (use -q to disable)
• Does not accept input from console (but accepts stdin when piped)
• Does not store filename or attributes, only file contents

File Handling

Reading from stdin

# Compress from stdin
cat file.txt | zstd > file.txt.zst

# Using dash for stdin
zstd - < file.txt > file.txt.zst

Recursive compression

# Compress all files in directory
zstd -r directory/

# With specific compression level
zstd -r -10 directory/

Output directory options

# Store files in flat directory
zstd -r --output-dir-flat /output/dir input/

# Preserve directory structure
zstd -r --output-dir-mirror /output/dir input/

Symlink Shortcuts

zstd can be invoked through symlinks with special behavior:

Symlink	Behavior
zstdmt	Compress using all CPU cores (zstd -T0)
unzstd	Decompress files
zstdcat	Decompress to stdout
zcat	Same as zstdcat

Environment Variables

Only ZSTD_CLEVEL and ZSTD_NBTHREADS are supported for security reasons.

ZSTD_CLEVEL

Set default compression level (1-19):

export ZSTD_CLEVEL=5
zstd file.txt  # Uses level 5

ZSTD_NBTHREADS

Set default number of threads:

export ZSTD_NBTHREADS=4
zstd file.txt  # Uses 4 threads

These can be overridden by command-line arguments (-# and -T#).

Concatenation

Multiple .zst files can be concatenated and decompressed as a single file:

cat file1.zst file2.zst file3.zst > combined.zst
zstd -d combined.zst

Integer Suffixes

Many options accept integer suffixes for convenience:

# These are equivalent
zstd -B 1048576 file.txt
zstd -B 1MiB file.txt
zstd -B 1MB file.txt

Supported suffixes:

• KiB, Ki, K, KB = × 1,024
• MiB, Mi, M, MB = × 1,048,576

Parameter Aggregation

CLI supports parameter aggregation:

# These are equivalent
zstd -b1 -e18 -i1 file.txt
zstd -b1e18i1 file.txt