How to compare the content of a tarball with a folder

Question

How can I compare a tar file (already compressed) of the original folder with the original folder?

First I created archive file using

tar -         


        

Answer 1

The method of pix is way slow for large compressed tar files, because it extracts each file individually. I use the tar --diff method loking for files with different modification time and extract and diff only these. The files are extracted into a folder base.orig where base is either the top level folder of the tar file or teh given comparison folder. This results in diffs including the date of the original file.

Here is the script:

#!/bin/bash
set -o nounset

# Print usage

if [ "$#" -lt 1 ] ; then
  echo 'Diff a tar (or compressed tar) file with a folder'
  echo 'difftar-folder.sh  [] [strip]'
  echo default for folder is .
  echo default for strip is 0.
  echo 'strip must be 0 or 1.'
  exit 1
fi

# Parse parameters

tarfile=$1

if [ "$#" -ge 2 ] ; then
  folder=$2
else
  folder=.
fi

if [ "$#" -ge 3 ] ; then
  strip=$3
else
  strip=0
fi

# Get path prefix if --strip is used

if [ "$strip" -gt 0 ] ; then
  prefix=`tar -t -f $tarfile | head -1`
else
  prefix=
fi

# Original folder

if [ "$strip" -gt 0 ] ; then
  orig=${prefix%/}.orig
elif [ "$folder" = "." ] ; then
  orig=${tarfile##*/}
  orig=./${orig%%.tar*}.orig
elif [ "$folder" = "" ] ; then
  orig=${tarfile##*/}
  orig=${orig%%.tar*}.orig
else
  orig=$folder.orig
fi
echo $orig
mkdir -p "$orig"


# Make sure tar uses english output (for Mod time differs)
export LC_ALL=C

# Search all files with a deviating modification time using tar --diff
tar --diff -a -f "$tarfile" --strip $strip --directory "$folder" | grep "Mod time differs" | while read -r file ; do
  # Substitute ': Mod time differs' with nothing
  file=${file/: Mod time differs/}
  # Check if file exists
  if [ -f "$folder/$file" ] ; then 
    # Extract original file
    tar -x -a -f "$tarfile" --strip $strip --directory "$orig" "$prefix$file"
    # Compute diff
    diff -u "$orig/$file" "$folder/$file" 
  fi
done