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Implementation
Read four hexadecimal byte values from stdin (separated by whitespace, e.g. "7f 45 4c 46").
Print exactly:
"ELF" if the bytes are 0x7f 0x45 0x4c 0x46
"not ELF" otherwise
This mirrors the first check every binary loader performs.
Why This Matters
The magic-byte check you write here is literally the first line of defense in the Linux kernel's binfmt_elf loader and the core mechanism of the file(1) command. Security tools like YARA and antivirus engines scan for magic signatures at scale, and forensic analysts recover deleted files from disk images by hunting for them.