Pad a file with zeros
Bash + coreutils, 13
truncate -s$@
Input from the command-line - the first parameter is the file size and the second is the filename.
From man truncate
:
If a FILE is shorter, it is extended and the extended part (hole) reads as zero bytes.
Try it online.
Groovy, 54 47 43 41 bytes
{a,b->(c=new File(a))<<'\0'*(b-c.size())}
-6 thanks to manatwork's idea of removing the loop; that was my original idea, don't know why I thought it wouldn't work and opted for a loop... It definitely works, just tested it.
Ungolfed:
{
a,b-> // Two inputs: a is the File name, b is the desired size.
File c = new File(a) // Make and store the file.
c << '\0'*(b-c.size()) // Append the difference between b and c.size() in nullbytes.
}
// Usually a close would be required, but, in Groovy,
// because private data isn't so protected, if a File
// Object goes out of scope, the attached Stream is
// automatically flushed to disk.
APL (Dyalog), 33 17 bytes
⎕⎕NRESIZE⍞⎕NTIE¯1
Try it online!