how to use patch and diff to merge two files and automatically resolve conflicts

Question

I have read about diff and patch but I can't figure out how to apply what I need. I guess its pretty simple, so to show my problem take these two files:

a.xml

<resources>
   <color name="same_in_b">#AAABBB</color>
   <color name="not_in_b">#AAAAAA</color>
   <color name="in_b_but_different_val">#AAAAAA</color>
   <color name="not_in_b_too">#AAAAAA</color>
</resources>

b.xml

<resources>
   <color name="same_in_b">#AAABBB</color>
   <color name="in_b_but_different_val">#BBBBBB</color>
   <color name="not_in_a">#AAAAAA</color>
</resources>

I want to have an output, which looks like this (order doesn't matter):

<resources>
   <color name="same_in_b">#AAABBB</color>
   <color name="not_in_b">#AAAAAA</color>
   <color name="in_b_but_different_val">#BBBBBB</color>
   <color name="not_in_b_too">#AAAAAA</color>
   <color name="not_in_a">#AAAAAA</color>
</resources>

The merge should contain all lines along this simple rules:

1. any line which is only in one of the files
2. if a line has the same name tag but a different value, take the value from the second

I want to apply this task inside a bash script, so it must not nessesarily need to get done with diff and patch, if another programm is a better fit

Answer 1

You don't need patch for this; it's for extracting changes and sending them on without the unchanged part of the file.

The tool for merging two versions of a file is merge, but as @vonbrand wrote, you need the "base" file from which your two versions diverged. To do a merge without it, use diff like this:

diff -DVERSION1 file1.xml file2.xml > merged.xml

It will enclose each set of changes in C-style #ifdef/#ifndef "preprocessor" commands, like this:

#ifdef VERSION1
<stuff added to file1.xml>
#endif
...
#ifndef VERSION1
<stuff added to file2.xml>
#endif

If a line or region differs between the two files, you'll get a "conflict", which looks like this:

#ifndef VERSION1
<version 1>
#else /* VERSION1 */
<version 2>
#endif /* VERSION1 */

So save the output in a file, and open it in an editor. Search for any places where #else comes up, and resolve them manually. Then save the file and run it through grep -v to get rid of the remaining #if(n)def and #endif lines:

grep -v '^#if' merged.xml | grep -v '^#endif' > clean.xml

In the future, save the original version of the file. merge can give you much better results with the help of the extra information. (But be careful: merge edits one of the files in-place, unless you use -p. Read the manual).

Answer 2

sdiff (1) - side-by-side merge of file differences

Use the --output option, this will interactively merge any two files. You use simple commands to select a change or edit a change.

You should make sure that the EDITOR environment variable is set. The default editor for commands like "eb" is usually ed, a line editor.

EDITOR=nano sdiff -o merged.txt file1.txt file2.txt

Answer 3

merge(1) is probably nearer to what you want, but that requires a common ancestor to your two files.

A (dirty!) way of doing it is:

1. Get rid of the first and last lines, use grep(1) to exclude them
2. Smash the results together
3. sort -u leaves a sorted list, eliminates duplicates
4. Replace first/last line

Humm... something along the lines:

echo '<resources>'; grep -v resources file1 file2 | sort -u; echo '</resources>'

might do.

Answer 4

Here a simple solution that works merging up to 10 files:

#!/bin/bash

strip(){
    i=0
    for f; do
        sed -r '
            /<\/?resources>/ d
            s/>/>'$((i++))'/
        ' "$f"
    done
}

strip "$@" | sort -u -k1,1 -t'>' | sed '
    1 s|^|<resources>\n|
    s/>[0-9]/>/
    $ a </resources>
'

please note the arg that comes first has the precedence so you have to call:

script b.xml a.xml

to get common values kept from b.xml rather than a.xml.

script b.xml a.xml outs:

<resources>
   <color name="in_b_but_different_val">#BBBBBB</color>
   <color name="not_in_a">#AAAAAA</color>
   <color name="not_in_b">#AAAAAA</color>
   <color name="not_in_b_too">#AAAAAA</color>
   <color name="same_in_b">#AAABBB</color>
</resources>

Answer 5

Another horrible hack - could be simplified, but :P

#!/bin/bash

i=0

while read line
do
    if [ "${line:0:13}" == '<color name="' ]
    then
        a_keys[$i]="${line:13}"
        a_keys[$i]="${a_keys[$i]%%\"*}"
        a_values[$i]="$line"
        i=$((i+1))
    fi
done < a.xml

i=0

while read line
do
    if [ "${line:0:13}" == '<color name="' ]
    then
        b_keys[$i]="${line:13}"
        b_keys[$i]="${b_keys[$i]%%\"*}"
        b_values[$i]="$line"
        i=$((i+1))
    fi
done < b.xml

echo "<resources>"

i=0

for akey in "${a_keys[@]}"
do
    print=1

    for bkey in "${b_keys[@]}"
    do
        if [ "$akey" == "$bkey" ]
        then
            print=0
            break
        fi
    done

    if [ $print == 1 ]
    then
        echo "  ${a_values[$i]}"
    fi

    i=$(($i+1))
done

for value in "${b_values[@]}"
do
    echo "  $value"
done

echo "</resources>"

Answer 6

OK, second try, now in Perl (not production quality, no checking!):

#!/usr/bin/perl

open(A, "a.xml");

while(<A>) {
  next if(m;^\<resource\>$;);
  next if(m;^\<\/resource\>$;);
  ($name, $value) = m;^\s*\<color\s+name\s*\=\s*\"([^"]+)\"\>([^<]+)\<\/color\>$;;
  $nv{$name} = $value if $name;
}

close(A);

open(B, "b.xml");

while(<B>) {
  next if(m;^\<resource\>$;);
  next if(m;^\<\/resource\>$;);
  ($name, $value) = m;^\s*\<color\s+name\s*\=\*\"([^"]+)\"\>([^<]+)\<\/color\>$;;
  $nv{$name} = $value if $name;
}

close(B);

print "<resource>\n";
foreach (keys(%nv)) {
    print "   <color name=\"$_\">$nv{$_}</color>\n";
}
print "</resource>\n";

Answer 7

Another one, using cut and grep... (takes a.xml b.xml as arguments)

#!/bin/bash

zap='"('"`grep '<color' "$2" | cut -d '"' -f 2 | tr '\n' '|'`"'")'
echo "<resources>"
grep '<color' "$1" | grep -E -v "$zap"
grep '<color' "$2"
echo "</resources>"

Answer 8

you can also use join:

JOIN(1)                            User Commands                            JOIN(1)

NAME
       join - join lines of two files on a common field

SYNOPSIS
       join [OPTION]... FILE1 FILE2

DESCRIPTION
       For each pair of input lines with identical join fields, write a line to
       standard output. The default join field is the first, delimited by blanks.

i found it here: https://stackoverflow.com/questions/10364455/merge-two-files-by-key-if-exists-in-the-first-file-bash-script