(Tcl) Determine File Type from Binary Content of File

Note: This example requires Chilkat v9.5.0.64 or later.

Many file types have "signatures" (leading bytes) that signify the type of file. It allows for programs to identify the likely type of file given the first few bytes contained within the file. This example shows how to identify a few common types files. For other file types, you can do a short bit of investigative work by examining the first few bytes of an sample file, and searching the Internet for information about the file type. Use this same technique for handling other file types that have leading "signature" bytes.

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load ./chilkat.dll

# Note: This example requires Chilkat v9.5.0.64 or later.

# To identify a file by the first few bytes, we'll load a few bytes from the start
# of the file, and then examine the bytes as both hex and quoted-printable.

set fac [new_CkFileAccess]

# A JPG file.
set jpgData [new_CkBinData]

CkFileAccess_OpenForRead $fac "qa_data/jpg/starfish.jpg"
# The the first 8 bytes of the JPG file.
CkFileAccess_FileReadBd $fac 8 $jpgData
CkFileAccess_FileClose $fac

# JPG hex: FFD8FFE000104A46
# JPG qp: =FF=D8=FF=E0=00=10JF
puts "JPG hex: [CkBinData_getEncoded $jpgData hex]"
puts "JPG qp: [CkBinData_getEncoded $jpgData qp]"

# A JPG begins with the following two bytes: 0xFF, 0xD8
# Your program can check to see if the hex string begins with "FFD8", or if the qp string begins with "=FF=D8".

# ----------------------------------------
# A PNG file.
set pngData [new_CkBinData]

CkFileAccess_OpenForRead $fac "qa_data/png/anemone.png"
# The the first 8 bytes of the PNG file.
CkFileAccess_FileReadBd $fac 8 $pngData
CkFileAccess_FileClose $fac

# PNG hex: 89504E470D0A1A0A
# PNG qp: =89PNG=1A=0A
puts "PNG hex: [CkBinData_getEncoded $pngData hex]"
puts "PNG qp: [CkBinData_getEncoded $pngData qp]"
# A PNG file begins with the byte 0x89, followed by the us-ascii bytes "PNG".

# ----------------------------------------
# A PDF file.
set pdfData [new_CkBinData]

CkFileAccess_OpenForRead $fac "qa_data/pdf/fishing.pdf"
# The the first 8 bytes of the PDF file.
CkFileAccess_FileReadBd $fac 8 $pdfData
CkFileAccess_FileClose $fac

# PDF hex: 255044462D312E33
# PDF qp: %PDF-1.3
puts "PDF hex: [CkBinData_getEncoded $pdfData hex]"
puts "PDF qp: [CkBinData_getEncoded $pdfData qp]"
# A PDF file begins with the us-ascii chars "%PDF"

# ----------------------------------------
# A Zip file.
set zipData [new_CkBinData]

CkFileAccess_OpenForRead $fac "qa_data/zips/test.zip"
# The the first 8 bytes of the Zip file.
CkFileAccess_FileReadBd $fac 8 $zipData
CkFileAccess_FileClose $fac

# PDF hex: 504B030414000000
# PDF qp: PK=03=04=14=00=00=00
puts "PDF hex: [CkBinData_getEncoded $zipData hex]"
puts "PDF qp: [CkBinData_getEncoded $zipData qp]"
# A Zip archive begins with the us-ascii chars "PK" followed by the bytes 0x03, 0x04.

delete_CkFileAccess $fac
delete_CkBinData $jpgData
delete_CkBinData $pngData
delete_CkBinData $pdfData
delete_CkBinData $zipData