How to diff only the first line of two files?
Here you go:
diff <(head -n 1 file1) <(head -n 1 file2)
(this would return nothing what-so-ever).
diff <(head -n 2 file1) <(head -n 2 file2)
Returns:
2c2
< 1
---
> 3
You could incorporate that into a script to do the things you mention.
#!/bin/bash
fileOne=${1}
fileTwo=${2}
numLines=${3:-"1"}
diff <(head -n ${numLines} ${fileOne}) <(head -n ${numLines} ${fileTwo})
To use that, just make the script executable with chmod +x nameofscript.sh
and then to execute, ./nameofscript.sh ~/file1 ~/Docs/file2
That leaves the default # of lines at 1, if you want more append a number to the end of that command.
(Or you could do switches in your script with -f1 file1 -f2 file2 -n 1, but I don't recall of the top of my head the case statement for that).
head
returns from the beginning the # of lines as suggested by -n
. If you were to want to do reverse, it would be tail -n ${numLines}
(tail does from the end back the number of lines).
Edit 5/10/16:
This is specific to Bash (and compatible shells). If you need to use this from something else:
bash -c 'diff <(...) <(...)'