Function Repository Resource:

BinaryWriteAt

Source Notebook

Overwrite part of a file with binary data

Contributed by: Richard Hennigan (Wolfram Research)

ResourceFunction["BinaryWriteAt"][path,bytes,offset]

writes bytes to path beginning at the position given by offset.

ResourceFunction["BinaryWriteAt"][path,bytes]

uses an offset of zero.

Details and Options

The value for path can be any of the following:

"file"

a string corresponding to a local file path

File["file"]

a local file path

The value for bytes can be any of the following:

"str"

a string

ByteArray[…]

a byte array

{b₁,b₂,…}

a sequence of byte values given as integers

Negative values for offset can be given to specify an offset from the end of the file.

ResourceFunction["BinaryWriteAt"] accepts the CharacterEncoding option, which specifies how strings should be converted to byte values before writing.

The CharacterEncoding option has no effect if bytes is not a string.

Examples

Basic Examples (3)

Create a test file:

In[1]:=

Out[1]=

Overwrite the first few bytes of the file with new data:

In[2]:=

Out[2]=

Overwrite a different part of the file:

In[3]:=

Out[3]=

In[4]:=

Out[4]=

In[5]:=

Scope (2)

Use a negative value to specify an offset from the end of the file:

In[6]:=

In[7]:=

Out[7]=

In[8]:=

Use UpTo to avoid out-of-range errors:

In[9]:=

In[10]:=

Out[10]=

In[11]:=

Out[11]=

In[12]:=

Out[12]=

In[13]:=

Options (4)

CharacterEncoding (4)

Create a test file with "ISO8859-7" character encoding:

In[14]:=

$ba = StringToByteArray[ "\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]\[Alpha]", "ISO8859-7"]; file = Export[CreateFile[], ba, "Binary"];$