Linux – Diff: How to only compare the first n characters in each line

I think you can use a tool such as xmldiff for this purposes.

http://diffxml.sourceforge.net/

On the tools webpage it states:

The standard Unix tools diff and patch are used to find the differences between text files and to apply the differences. These tools operate on a line by line basis using well-studied methods for computing the longest common subsequence (LCS).

Using these tools on hierarchically structured data (XML etc) leads to sub-optimal results, as they are incapable of recognizing the tree-based structure of these 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 <(...) <(...)'