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I have some sql dumps that I am looking at the differences between. diff can obviously show me the difference between two lines, but I'm driving myself nuts trying to find which values in the long list of comma-separated values are actually the ones causing the lines to be different.

What tool can I use to point out the exact character differences between two lines in certain files?

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There's wdiff, the word-diff for that.

On desktop, meld can highlight the differences within a line for you.

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Colored wdiff: wdiff -w "$(tput bold;tput setaf 1)" -x "$(tput sgr0)" -y "$(tput bold;tput setaf 2)" -z "$(tput sgr0)" file1 file2 – l0b0 Apr 12 '11 at 11:21
For color, install colordiff, then do: wdiff a b | colordiff – philfreo Sep 28 '13 at 3:36

I've used vimdiff for this.

Here's a screenshot (not mine) showing minor one or two character differences that stands out pretty well. A quick tutorial too.

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In my case couldn't spot the difference so opened the files in gvim -d f1 f2 the particular long lines were both highlighted as being different however the actual difference was extra highlighted in red – zzapper Dec 9 '15 at 16:54

Here is a "..hair of the dog that bit you" method...
diff got you to this point; use it to take you further...

Here is the output from using the sample line pairs... indicates a TAB

Paris in the     spring 
Paris in the the spring 
             vvvv      ^

A ca t on a hot tin roof.
a cant on a hot  in roof 
║   v           ^       ^

the quikc brown box jupps ober the laze dogs 
The☻qui ckbrown fox jumps over the lazy dogs 
║  ║   ^ ║      ║     ║    ║          ║     ^

Here is the script.. You just need to ferret out the line pairs somehow.. (I've used diff only once (twice?) before today, so I don't know its many options, and sorting out the options for this script was enough for me, for one day :) .. I think it must be simple enough, but I'm due for a coffee break ....

# Name: hair-of-the-diff
# Note: This script hasn't been extensively tested, so beware the alpha bug :) 
# Brief: Uses 'diff' to identify the differences between two lines of text
#        $1 is a filename of a file which contains line pairs to be processed
#        If $1 is null "", then the sample pairs are processed (see below: Paris in the spring 
# ║ = changed character
# ^ = exists if first line, but not in second 
# v = exists if second line, but not in first

bname="$(basename "$0")"
workd="/tmp/$USER/$bname"; [[ ! -d "$workd" ]] && mkdir -p "$workd"

# Use $1 as the input file-name, else use this Test-data
# Note: this test loop expands \t \n etc ...(my editor auto converts \t to spaces) 
if [[ "$1" == '' ]] ;then
{ while IFS= read -r line ;do echo -e "$line" ;done <<EOF
Paris in the spring 
Paris in the the spring
A cat on a hot tin roof.
a cant on a hot in roof
the quikc brown box jupps ober the laze dogs 
The\tquickbrown fox jumps over the lazy dogs
} >"$ifile"
[[ -f "$ifile" ]] || { echo "ERROR: Input file NOT found:" ;echo "$ifile" ;exit 1 ; }
# Check for balanced pairs of lines
ilct=$(<"$ifile" wc -l)
((ilct%2==0)) || { echo "ERROR: Uneven number of lines ($ilct) in the input." ;exit 2 ; }
ifs="$IFS" ;IFS=$'\n' ;set -f
ix=0 ;left=0 ;right=1
while IFS= read -r line ;do
  pair[ix]="$line" ;((ix++))
  if ((ix%2==0)) ;then
    # Change \x20 to \x02 to simplify parsing diff's output,
    #+   then change \x02 back to \x20 for the final output. 
    # Change \x09 to \x01 to simplify parsing diff's output, 
    #+   then change \x01 into ☻ U+263B (BLACK SMILING FACE) 
    #+   to the keep the final display columns in line. 
    #+   '☻' is hopefully unique and obvious enough (otherwise change it) 
    diff --text -yt -W 19  \
         <(echo "${pair[0]}" |sed -e "s/\x09/\x01/g" -e "s/\x20/\x02/g" -e "s/\(.\)/\1\n/g") \
         <(echo "${pair[1]}" |sed -e "s/\x09/\x01/g" -e "s/\x20/\x02/g" -e "s/\(.\)/\1\n/g") \
     |sed -e "s/\x01/☻/g" -e "s/\x02/ /g" \
     |sed -e "s/^\(.\) *\x3C$/\1 \x3C  /g" \
     |sed -n "s/\(.\) *\(.\) \(.\)$/\1\2\3/p" \
     # (gedit "$workd/out" &)
     <"$workd/out" sed -e "s/^\(.\)..$/\1/" |tr -d '\n' ;echo
     <"$workd/out" sed -e "s/^..\(.\)$/\1/" |tr -d '\n' ;echo
     <"$workd/out" sed -e "s/^.\(.\).$/\1/" -e "s/|/║/" -e "s/</^/" -e "s/>/v/" |tr -d '\n' ;echo
done <"$ifile"
IFS="$ifs" ;set +f
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  • xxdiff: Another tool is xxdiff (GUI), which has to be installed, first.
  • spreadsheet: For database data, a spreadsheet from .csv is easily made, and a formula (A7==K7) ? "" : "diff" or similar inserted, and copy-pasted.
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On the command line, I would make sure I add judicious new-lines before comparing files. You can use sed, awk, perl or anything really to add line breaks in some sort of systematic way - make sure not to add too many though.

But I find the best is to use vim as it highlights word differences. vim is good if there are not too many differences and the differences are simple.

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Although not really an answer to the question this technique is rather efficient to learn about small differences in long lines. – jknappen Feb 4 '15 at 19:05

kdiff3 is becoming the standard GUI diff viewer on Linux. It is similar to xxdiff, but I think kdiff3 is better. It does many things well, including your request to show "exact character differences between two lines in certain files".

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If I'm reading your question correctly, I use diff -y for this kind of thing.

It makes comparing a side by side comparison much simpler to find which lines are throwing the differences.

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I had the same problem and solved it with PHP Fine Diff, an online tool that allows you to specify granularity. I know it's not technically a *nix tool, but I didn't really want to download a program just to do a one-time, character level diff.

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