57 Backing Up Directories

#57 Backing Up Directories

Related to the task of backing up entire file systems is the user -centric task of taking a snapshot of a specific directory or directory tree. This simple script allows users to easily create a compressed tar archive of a specified directory.

The Code

 #!/bin/sh # archivedir - Creates a compressed archive of the specified directory. maxarchivedir=10        # size, in blocks, of 'big' directory compress=gzip           # change to your favorite compress app progname=$(basename 
 #!/bin/sh # archivedir - Creates a compressed archive of the specified directory. maxarchivedir=10 # size , in blocks, of 'big' directory compress=gzip # change to your favorite compress app progname=$(basename $0) if [ $# -eq 0 ] ; then echo "Usage: $progname directory" >&2 ;exit 1 fi if [ ! -d $1 ] ; then echo "${progname}: can't find directory $1 to archive." >&2; exit 1 fi if [ "$(basename $1)" != "$1" -o "$1" = "." ] ; then echo "${progname}: You must specify a subdirectory" >&2 exit 1 fi if [ ! -w . ] ; then echo "${progname}: cannot write archive file to current directory." >&2 exit 1 fi dirsize="$(du -s $1  awk '{print $1}')" if [ $dirsize -gt $maxarchivedir ] ; then echo -n "Warning: directory $1 is $dirsize blocks. Proceed? [n] " read answer answer="$(echo $answer  tr '[:upper:]' '[:lower:]'  cut -c1)" if [ "$answer" != "y" ] ; then echo "${progname}: archive of directory $1 canceled ." >&2 exit 0 fi fi archivename="$(echo $1  sed 's/$/.tgz/')" if tar cf - $1  $compress > $archivename ; then echo "Directory $1 archived as $archivename" else echo "Warning: tar encountered errors archiving $1" fi exit 0 
 ) if [ $# -eq 0 ] ; then   echo "Usage: $progname directory" >&2 ;exit 1 fi if [ ! -d  ] ; then   echo "${progname}: can't find directory  to archive." >&2; exit 1 fi if [ "$(basename )" != "" -o "" = "." ] ; then   echo "${progname}: You must specify a subdirectory" >&2   exit 1 fi if [ ! -w . ] ; then   echo "${progname}: cannot write archive file to current directory." >&2   exit 1 fi dirsize="$(du -s   awk '{print }')" if [ $dirsize -gt $maxarchivedir ] ; then   echo -n "Warning: directory  is $dirsize blocks. Proceed? [n] "   read answer   answer="$(echo $answer  tr '[:upper:]' '[:lower:]'  cut -c1)"   if [ "$answer" != "y" ] ; then     echo "${progname}: archive of directory  canceled." >&2     exit 0   fi fi archivename="$(echo   sed 's/$/.tgz/')" if tar cf -   $compress > $archivename ; then   echo "Directory  archived as $archivename" else   echo "Warning: tar encountered errors archiving " fi exit 0 

How It Works

This script is almost all error-checking code, to ensure that it never causes a loss of data or creates an incorrect snapshot. In addition to the typical tests to validate the presence and appropriateness of the starting argument, this script also forces the user to be in the parent directory of the subdirectory to be compressed and archived, which ensures that the archive file is saved in the proper place upon completion. The conditional if [ ! -w . ] ; then verifies that the user has write permission on the current directory. And this script even warns users before archiving if the resultant backup file would be unusually large.

Finally, the actual command that archives the specified directory is

 tar cf -   $compress > $archivename 

The return code of this command is tested to ensure that the script never deletes the directory if an error of any sort occurs.

Running the Script

This script should be invoked with the name of the desired directory to archive as its only argument. To ensure that the script doesn't try to archive itself, it requires that a subdirectory of the current directory be specified as the argument, rather than ".".

The Results

 $  archivedir scripts  Warning: directory scripts is 2224 blocks. Proceed? [n]  n  archivedir: archive of directory scripts canceled. 

This seemed as though it might be a big archive, so I hesitated to create it, but thinking about it, there's no reason not to proceed after all:

 $  archivedir scripts  Warning: directory scripts is 2224 blocks. Proceed? [n]  y  Directory scripts archived as scripts.tgz 

The results:

 $  ls -l scripts.tgz  -rw-r--r--  1 taylor  staff  325648 Jul 14 08:01 scripts.tgz 

Helpful for developers  

When I'm actively working on a project, I use archivedir in a cron job to automatically take a snapshot of my working code each night for archival purposes.