How do I trim bytes from the beginning and end of a file?

You can combine GNU tail and head:

tail -c +26 file | head -c -2

will output the contents of file starting at byte 26, and stopping two bytes (minus two -2) before the end. (-c operates on bytes, not characters.)

dd will do both for you in a single command. Set the block size to 1 byte, skip the 25 first bytes, count to the size of file minus skip and end bytes.

100 byte file
file.img

dd if=./file.img of=./trimed_file.img bs=1 skip=25 count=73

Double check numbers cause it might count from 0.

With ksh93:

{ head -c "$n"; } < file <#((n = EOF - 25 - 2 , 25))

Or to do it in-place:

{ head -c "$n"; } < file <#((n = EOF - 25 - 2 , 25)) 1<>; file

If you have /opt/ast/bin ahead of your $PATH, you'll get the head builtin.

• <#((...)) is a lseek() operator. ... is interpreted as an arithmetic expression where EOF is the length of the file. So above, we're assigning the length of the portion to display to $n and seeking to 25 bytes within the file.
• <>; is a open-in-read+write-mode-and-truncate-if-the-command-is-successful redirection operator.