Tcl

Compress a File to Gzip with Custom Metadata

See more Gzip Examples

This example demonstrates how to use the CompressFile method to create a Gzip (.gz) file while customizing the metadata embedded in the Gzip header.

Before compression, several properties are set:

• Comment: Adds a descriptive comment to the Gzip file.
• Filename: Specifies the filename to embed in the Gzip data, which may be used by extraction tools as the default output name.
• CompressionLevel: Controls the tradeoff between compression ratio and speed (set to maximum in this example).
• LastModStr: Sets the last-modified timestamp using an RFC 822 formatted date string.

After setting these properties, the input file is compressed and written to a .gz file. This approach allows you to embed meaningful metadata along with the compressed data.

Tcl

load ./chilkat.dll

set success 0

# This example demonstrates how to compress a file to Gzip format
# while setting custom metadata such as comment, filename,
# compression level, and last-modified date.

set gzip [new_CkGzip]

# Set custom Gzip properties:
CkGzip_put_Comment $gzip "Example Gzip file created with Chilkat"
CkGzip_put_Filename $gzip "custom_name.txt"
CkGzip_put_CompressionLevel $gzip 9
CkGzip_put_LastModStr $gzip "Wed, 1 Apr 2025 12:45:26 -0500"

# The file to be compressed:
set inputFile "example.txt"
set outputFile "example.txt.gz"

# Compress the file:
set success [CkGzip_CompressFile $gzip $inputFile $outputFile]
if {$success == 0} then {
    puts [CkGzip_lastErrorText $gzip]
    delete_CkGzip $gzip
    exit
}

puts "Compression successful."
puts "Gzip file created: $outputFile"

delete_CkGzip $gzip