With cargo (rust package manager)
cargo install mf
This merges file 1.txt and 2.txt into one file called target.txt
mf -m target.txt 1.txt 2.txt
mf <mode> [file ... file ... file]
modes:
-h: Help | -c Create file/s | -m Merge file/s | -r Delete file/s
!! If the mode is merge, first file is target file name !!