Decompression Commands

Decompression commands and options for zstd command-line tool

The zstd CLI provides fast and flexible decompression capabilities with various output and validation options.

Basic Decompression

Standard Decompression

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

# Alternative syntax
zstd --decompress file.txt.zst
unzstd file.txt.zst

Decompress to stdout

# Write to stdout
zstd -dc file.txt.zst
zstd -d -c file.txt.zst

# Using symlinks
zstdcat file.txt.zst
zcat file.txt.zst

Specify Output File

# Decompress to specific file
zstd -d file.txt.zst -o output.txt

# Keep compressed file (default)
zstd -d -k file.txt.zst

# Remove compressed file after decompression
zstd -d --rm file.txt.zst

File Information

List File Details

# Display information about compressed file
zstd -l file.txt.zst

# Verbose information
zstd -lv file.txt.zst

Displays information such as:

• Original size
• Compressed size
• Compression ratio
• Checksum (if available)

Some fields may not be available depending on how the file was compressed (e.g., missing content size if compressed with --no-content-size).

Integrity Testing

Test Compressed Files

# Test file integrity without decompressing
zstd -t file.txt.zst
zstd --test file.txt.zst

# Test multiple files
zstd -t *.zst

This is equivalent to zstd -d --stdout > /dev/null. Data is decompressed and checksummed but discarded. No files are created or removed.

Checksum Validation

# Validate checksums during decompression (default)
zstd -d file.txt.zst

# Ignore checksums
zstd -d --no-check file.txt.zst

Memory Limits

Set Memory Usage Limit

# Limit decompression memory to 256 MiB
zstd -d -M 256MiB file.txt.zst

# Limit to 128 MiB (default)
zstd -d -M 128MiB file.txt.zst

If a compressed file requires more memory than the limit allows, decompression will fail. This is particularly relevant for files compressed with high windowLog values or --long mode.

Large Window Sizes

For files compressed with windowLog > 27:

# Decompress with large window (from --long=30)
zstd -d --long=30 file.txt.zst

# Or specify memory directly
zstd -d --memory=1GiB file.txt.zst

Sparse Files

Sparse Mode

# Enable sparse file support (default for files)
zstd -d --sparse file.txt.zst

# Disable sparse mode
zstd -d --no-sparse file.txt.zst

# Force sparse mode for stdout
zstd -dc --sparse file.txt.zst

Sparse mode is enabled by default when output is a file and disabled when output is stdout. Sparse files save disk space and speed up decompression by reducing I/O for files with many zeros.

Pass-through Mode

Handle Uncompressed Files

# Pass through uncompressed files as-is
zstd -d --pass-through file.txt

# Force pass-through to stdout
zstd -df --pass-through file.txt

With pass-through enabled, unrecognized formats are copied from input to output without modification. By default, pass-through occurs when output is stdout and -f is set.

Recursive Decompression

Decompress Directories

# Decompress all .zst files in directory
zstd -d -r directory/

# Output to flat directory
zstd -d -r --output-dir-flat /output/dir input/

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

Multiple File Decompression

File Lists

# Decompress files from list
zstd -d --filelist files.txt

# Create file list
ls *.zst > files.txt
zstd -d --filelist files.txt

Format is compatible with ls output, one file per line.

Wildcards

# Decompress multiple files
zstd -d *.zst
zstd -d file1.zst file2.zst file3.zst

Dictionary Decompression

Using Dictionaries

# Decompress with dictionary
zstd -d file.txt.zst -D dictionary

# Dictionary is required for files compressed with -D
zstd -d FILE.zst -D dictionaryName

Files compressed with a dictionary require that same dictionary for decompression. The decoder will verify the dictionary ID matches.

Memory-mapped Dictionaries

# Memory-map dictionary instead of loading it
zstd -d --mmap-dict -D large-dictionary file.txt.zst

# Disable memory mapping (default)
zstd -d --no-mmap-dict -D dictionary file.txt.zst

Progress and Output Control

Verbosity

# Verbose output
zstd -dv file.txt.zst

# Very verbose
zstd -dvv file.txt.zst

# Quiet mode (suppress warnings)
zstd -dq file.txt.zst

# Very quiet (suppress errors too)
zstd -dqq file.txt.zst

Progress Counter

# Force show progress
zstd -d --progress file.txt.zst

# Hide progress
zstd -d --no-progress file.txt.zst

Progress counter is shown by default for single file decompression. When output is mixed with progress text, use --no-progress.

Force Operations

Override Protections

# Force various operations
zstd -df file.txt.zst           # Overwrite existing files
zstd -df file.txt.zst > output  # Force stdout to terminal

The -f flag:

• Allows overwriting existing files
• Enables output to stdout even if it’s a terminal
• Enables pass-through of unrecognized formats
• Operates on links and block devices

Concatenated Files

# Decompress concatenated .zst files
zstd -d concatenated.zst

Multiple .zst files concatenated together are decompressed as if they were a single file:

cat file1.zst file2.zst file3.zst > combined.zst
zstd -d combined.zst
# Outputs: combined (containing data from all three files)

Asynchronous I/O

# Use async I/O (default)
zstd -d --asyncio file.txt.zst

# Disable async I/O
zstd -d --no-asyncio file.txt.zst

Format Detection

The CLI automatically detects compression format:

# Automatically detects .zst format
zstd -d file.txt.zst

# Can also decompress gzip (if compiled with zlib)
zstd -d file.txt.gz

# And xz/lzma (if compiled with lzma)
zstd -d file.txt.xz
zstd -d file.txt.lzma

# And lz4 (if compiled with lz4)
zstd -d file.txt.lz4

Trace Logging

# Log tracing information
zstd -d --trace trace.log file.txt.zst

Useful for debugging or performance analysis.