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<title>More 2 Cent Tips & Tricks Issue 16</title>
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<BODY BGCOLOR="#EEE1CC" TEXT="#000000" LINK="#0000FF" VLINK="#0020F0"
ALINK="#FF0000" >
<!--endcut ============================================================-->
<H4>&quot;Linux Gazette...<I>making Linux just a little more fun!</I>
&quot;</H4>
<P> <hr> <P> 

<!-- QUICK TIPS SECTION ==================================================  -->
<center>
<H1><A NAME="tips"><IMG ALIGN=MIDDLE ALT="" SRC="../gx/twocent.gif">
More 2&#162; Tips!</A></H1> <BR>
Send Linux Tips and Tricks to <A HREF="mailto:gazette@ssc.com">
gazette@ssc.com
</A></center>

<p><hr><p>
<H3>Contents:</H3>
<ul>
<li><a HREF="./lg_tips16.html#ftp">How to ftp Back Home</a>
<li><a HREF="./lg_tips16.html#root">Checking if You're Boot</a>
<li><a HREF="./lg_tips16.html#xv">XV vs Xli</a>
<li><a HREF="./lg_tips16.html#bash">Bash Shell Scripting</a>
<ul>
   <li><a HREF="./lg_tips16.html#scr1">Bash Shell Script 1</a>
   <li><a HREF="./lg_tips16.html#scr2">Bash Shell Script 2</a>
   <li><a HREF="./lg_tips16.html#scr3">Bash Shell Script 3</a>
</ul>
</ul>

<P> <hr> <P> 
<!--================================================================-->

<a name="ftp"></a>
<H3><IMG ALIGN=BOTTOM ALT="" SRC="../gx/lil2cent.gif">
How to ftp Back Home
</H3>
<p>
Date:Sat Mar 30 14:23:24 (PST)<BR>
From:Phil Hughes<a href="mailto:phil@ssc.com">phil@ssc.com</a><P>
<p>
Many businesses place a firewall between the Internet and the inside
systems.
This is good protection and it just makes good sense.
One common firewalling technique is to serverly restrict access through
the firewall from the outside but allow a user on the inside to do most
anything through the firewall to the outside.
<p>
When I am at home, I routinely need to move files between home and work.
But, because of the firewall, I can ftp from work to home but not the
other way around.
What this means is that I need to establish an interactive connection
(using ssh) from home to work and then initiate the ftp from work to home.
<p>
So far, so good.
But, what I call "home" consists of various locations, all connected with
a dial-up connection through one of four ISPs.
All four ISPs use dynamic IP addresses meaning that each time I connect I
have a different IP address for my home system.
Even though the ISP knows what the current IP address for my system, the
name server at work doesn't.
<p>
The solution is to enter the IP address of my home system into the ftp
command at work.
First, I need to find out what the IP address is.
To do that, I execute the ifconfig command on my home system:

<pre>
$ /sbin/ifconfig

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Bcast:127.255.255.255  Mask:255.0.0.0
          UP BROADCAST LOOPBACK RUNNING  MTU:2000  Metric:1
          RX packets:19 errors:0 dropped:0 overruns:0
          TX packets:19 errors:0 dropped:0 overruns:0

eth0      Link encap:10Mbps Ethernet  HWaddr 02:60:8C:8F:A2:08
          inet addr:198.186.207.131  Bcast:198.186.207.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:969719 errors:0 dropped:0 overruns:0
          TX packets:971132 errors:0 dropped:0 overruns:0
          Interrupt:9 Base address:0x280 Memory:d8000-da000 

ppp0      Link encap:Point-Point Protocol  
          inet addr:206.125.79.118  P-t-P:204.157.220.30  Mask:255.255.255.0
          UP POINTOPOINT RUNNING  MTU:296  Metric:1
          RX packets:5434 errors:0 dropped:0 overruns:0
          TX packets:5545 errors:0 dropped:0 overruns:0
$
</pre>

The inet addr for the ppp0 interface (206.125.79.118) is the number I
need.
Now, on my system at work I enter:

<pre>
$ ftp 206.125.79.118
</pre>

ftp then prompts for a login and password.
I enter my standard login and password for my home system and ftp is up
and running.




<P> <hr> <P> 
<!--================================================================-->

<a name="root"></a>
<H3><IMG ALIGN=BOTTOM ALT="" SRC="../gx/lil2cent.gif">
Checking if You're Root
</H3>
<P> 
Date: Sun Mar 23 23:20:51 1997 (PST)<BR> 
From: Kevin Lyda <a href="mailto:kevin@faxint.com">kevin@faxint.com</a> <BR> 
<P> 
<p>In the march gazette raul miller suggested that the most portable way to
test if you're root is [ -w / ].  that won't work if you're root file
system is read only.  [ -w /var ] might be a better method.
<p>
kevin

<P> <hr> <P> 
<!--================================================================-->

<a name="xv"></a>
<H3><IMG ALIGN=BOTTOM ALT="" SRC="../gx/lil2cent.gif">
XV vs Xli
</H3>
<P> 
Date:Wed Mar 5 16:32:49 1997(PST)<BR> 
From:Michael Hammel, <a
href="mailto:mjhammel@emass.com">mjhammel@emass.com</a><BR> 

<p>I wasn't aware of Xli (rather, I haven't looked at it), however
your statement that xv can only tile image on the background.  xv 
allows qutie a bit of command line control.  I use the following to
put up a background image at work (non-tiled, takes up the whole
background):

<pre><p>xv -root -max -quit /export/home/mjhammel/lib/images/emass3.tga
</pre>
<p>The initial image is 601x339, with a root display of 1152x900.  Since
the original image is 24bpp the enlargement is very accurate in 
details.
<p> 
Michael J. Hammel

<P> <hr> <P> 
<!--================================================================-->

<a name="bash"></a>
<H3><IMG ALIGN=BOTTOM ALT="" SRC="../gx/lil2cent.gif">
Bash Shell Scripting
</H3>
<P> 
Date:Thu Mar 20 12:22;34 1997(PST)<BR> 
From:Paul Sephton <a href="mailto:paul@inet.co.ca"> paul@inet.co.ca</a><BR> 

<p>I have been enjoying the fruits of the Linux Gazette for a number of
years now.  Recently, I had one of my users accidentally type rm *>bak,
and immediately noticed something was amiss by the incoherent screams
eminating from her office.

<p>In an attempt to ensure this would not have the same disasterous effect
again, and to protect my eardrums in future, I spent a couple of days
excersising my bash shell scripting skills, and came up with what I
believe to be a decent mechanism for maintaining versioned backups.

<p>My attitude with regard to the normal cludges like aliasing rm and so
on, is that it will not protect you against other programs which unlink
files. (To date I have yet to write a C program that shells rm in order
to unlink a file :)

<p>Whilst writing the set of three scripts, it dawned on me that although
some more complex tools do exist which perform the same sort of
function, the Linux community might be interested in what I did.  

<p>Although it's not much more than a creative excersise in the use of the
'find' command, and suffers from the usual limitation of being
restricted to the one file system, I include the three scripts for your
perusal and possible inclusion in the gazette at your discretion.

<p>Don't hesitate to contact me if you need more information.

<p>Kind regards, and many thanks for the gazette.<BR> 
Paul Sephton
<P> <hr> <P> 
<!--================================================================-->
<a name="scr1"></a>
<H3><IMG ALIGN=BOTTOM ALT="" SRC="../gx/lil2cent.gif">
Bash Shell Script 1
</H3>

<pre>#!/bin/sh
if [ -z "$SAFEDEL" ];then
SAFEDEL=/u/safedel
fi



NDAYS=5                        #Erase files after 2 days
MAXVER=6                       # Start Overwriting versins at this count
BINDIR=$SAFEDEL/bin            # Binaries directory
DATADIR=$SAFEDEL/data          # Where links are to go
LOGFILE=$BINDIR/safedel.log    # Output messages go here
ERRLOG=$BINDIR/safedel.err     # Error output messages go here
DIRLIST=$BINDIR/safedel.dirs   # List of directories found here
LOCKFILE=$BINDIR/safedel.lock  # Lockfile to prevent re-entry

#  Process the file $1 by creating a symbolic link in the data directory
#  and an entry for the file in the index.
process-file()
{
SRC=`dirname $1`
FNAME=`basename $1`
VERSION=0
if [ ! -d $DATADIR$SRC ]; then
mkdir -p $DATADIR$SRC
#  OWNER=`find -name $SRC -printf "%u"`
#  chown $OWNER $FNAME:$VERSION
fi
  cd $DATADIR$SRC
  while [ -f $FNAME:$VERSION ]; do
  VERSION=$[ $VERSION + 1 ]
  done
  if ! ln $1 $FNAME:$VERSION 2>> $LOGFILE; then
echo "Could not link file $FNAME:$VERSION" >> $LOGFILE
    return
fi 
echo -e "Linked $FNAME:$VERSION \t \tin $SRC" >> $LOGFILE
return
}

 # Erase a file
erase-file()
{
  echo "Unlinking $1 $2" >> $LOGFILE
  rm -f $1
  FN=`echo $1 | cut -f 1 -d ':'`
if ! { echo "$ERASED" | grep "$FN" - } ; then
    ERASED="$ERASED $FN"
  fi 
  return
}
# We want the version numbers to follow on each other, so that the next
# file we create gets a bigger version number. This makes sure they follow.
reorganise()
{
  if [ -z $1 ]; then
    return
  fi
  FN=$1
  FILE_LIST=`ls $FN:* | sort -n -t: -k2`
  if [ "$FILE_LIST" = ":*" ]; then
    echo "All [$FN:*] files erased" >> $LOGFILE
    return
  fi
  echo -e "File list to be moved is:\n$FILE_LIST" >>$LOGFILE
  VERSION=0
  for FNAME in $FILE_LIST; do
    if [ "$FNAME" != "$FN:$VERSION" ]; then
      echo "Moving $FNAME $FN:$VERSION" >>$LOGFILE
      mv $FNAME "$FN:$VERSION"
      VERSION=$[ $VERSION + 1 ]
    fi
  done
}

# The main shell script starts here...

cd $BINDIR
if [ -f $LOCKFILE ]; then
  exit 0
fi
touch $LOCKFILE
date >> $LOGFILE
cat $DIRLIST |
(
  while read SRC ; do
    if [ `echo $SRC | cut -b 1` != "#" ]; then
      echo "Finding files in $SRC" >> $LOGFILE
      echo "Point 1 ($SRC)"
      for FNAME in `find $SRC -type f -xdev -links 1 -print`; do
        process-file $FNAME
      done
    fi
  done
  ERASED=""
  echo "Point 2"
  for FNAME in `find $DATADIR -type f -links 1 -ctime $NDAYS -print`; do
    erase-file $FNAME "(older than $NDAYS days)"
  done
  echo "Point 3"
  for FNAME in `find $DATADIR -type f -name "*:$MAXVER" -print`; do
    FN=`echo $FNAME | cut -f 1 -d ':'`
    erase-file $FN:0 "Too many versions (VERSION > $MAXVER)"
  done
  echo "Point 4"
  for FNAME in "$ERASED"; do
    reorganise $FNAME
  done
) 2> $ERRLOG > /dev/null
rm -f $LOCKFILE
</PRE> 
<P> <hr> <P> 
<!--================================================================-->
<a name="scr2"></a>
<H3><IMG ALIGN=BOTTOM ALT="" SRC="../gx/lil2cent.gif">
Bash Shell Script 2 
</H3>

<PRE> 
#!/bin/sh
CURRDIR=`pwd`/
if [ -z $SAFEDEL ]; then
  SAFEDEL=/u/safedel
fi

DATADIR=$SAFEDEL/data
BINDIR=$SAFEDEL/bin
cd $DATADIR$CURRDIR
if [ -z "$1" ]; then
  echo
  echo "Restores files unintentionally deleted"
  echo
  echo "Useage &lt;salvage &lt;filename&gt;[:version] [dest]&gt; from within the directory"
  echo "       in which the file was deleted."
  echo
  echo "The following is a list of your backed up files and their versions:"
  echo "  Salvageable Files:"
  find . -xdev -type f -maxdepth 1 -links 1 -printf "%P\n" | column 
  echo "  Files Currently in Use:"
  find . -xdev -type f -maxdepth 1 -not -links 1 -printf "%P\n" | column 
else
  FN=`echo "$1:end" | cut -f 1 -d ':'`
  VER=`echo "$1:end" | cut -f 2 -d ':'`
  EXIST=`find $CURRDIR -name "$FN"`
#  echo "[$EXIST]"
  if [ -n "$EXIST" ]; then
    echo "Incorrect file specification: File(s) are not deleted. ($FN)"
    exit 0
  fi
  if [ "$VER" = "end" -o "$VER" = "*" ]; then
    VER=""
  fi
  FILE_LIST=`find . -name "$FN:*" -printf "%f "`
  FLIST=""
#  echo "FILE_LIST is $FILE_LIST"
  for FNAME in $FILE_LIST; do
    FN=`echo "$FNAME:end" | cut -f 1 -d ':'`
    FOUND=0
#    echo "Looking for [$FN] in [$FLIST]"
    for F in $FLIST; do
      if [ "$F" = "$FN" ]; then
        FOUND=1
      fi
    done
    if [ "$FOUND" = "0" ]; then
      FLIST="$FLIST $FN"
    fi
  done
#  echo "FLIST is $FLIST"
  for FNAME in $FLIST; do
    if [ -z "$VER" ]; then
      VERSION=0
      NEXTVER=1
      while [ -f $FNAME:$NEXTVER ]; do
        VERSION=$NEXTVER
        NEXTVER=$[ $NEXTVER + 1 ]
      done
    else
      VERSION=$VER
    fi

    if [ ! -f $FNAME:$VERSION ]; then 
      echo "File $FNAME:$VERSION not found"
      exit 0
    fi

    if [ -z "$2" ]; then
      DEST=$CURRDIR$FNAME
    else
      DEST=$CURRDIR$2
    fi

    if ln $FNAME:$VERSION $DEST 2> /dev/null; then
      echo "File $FNAME:$VERSION successfully recovered"
    else
      echo "Cannot link $FNAME:$VERSION to $DEST"
    fi
  done
fi
</PRE> 
<P> <hr> <P> 
<!--================================================================-->
<a name="scr3"></a>
<H3><IMG ALIGN=BOTTOM ALT="" SRC="../gx/lil2cent.gif">
Bash Shell Script 3 
</H3>

<PRE> 
#!/bin/sh

if [ -z $SAFEDEL ]; then
  SAFEDEL=/u/safedel
fi

BINDIR=$SAFEDEL/bin            # Binaries directory
DATADIR=$SAFEDEL/data          # Where links are to go

# Erase a file
reorganise()
{
  if [ -z $1 ]; then
    return
  fi
  FN=`echo "$1:end" | cut -f 1 -d ':'`
  FILE_LIST=`ls $FN:* | sort -n -t: -k2`
  if [ "$FILE_LIST" = ":*" ]; then
    echo "All [$FN:*] files erased" 
    return
  fi
#  echo -e "File list to be moved is:\n$FILE_LIST" 
  VERSION=0
  for FNAME in $FILE_LIST; do
    if [ "$FNAME" != "$FN:$VERSION" ]; then
      echo "Moving $FNAME $FN:$VERSION" 
      mv $FNAME "$FN:$VERSION"
      VERSION=$[ $VERSION + 1 ]
    fi
  done
}

# The main shell script starts here...

CURRDIR=`pwd`/

echo "Safedel: Purging extra versions in $CURRDIR"

cd $BINDIR
find $DATADIR$CURRDIR -type f -maxdepth 1 -links 1 -exec rm {} \;
for FNAME in `find $DATADIR$CURRDIR -type f -maxdepth 1 -print`; do
  reorganise $FNAME
done
</pre>
<P> <hr> <P> 
<!--================================================================-->
<center>Published in Linux Gazette Issue 16, April 1997</center>
<P> <HR> <P> 
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<h5>This page maintained by the Assistant Editor of <I>Linux Gazette</I>,
<A HREF="mailto: gazette@ssc.com">gazette@ssc.com</A><BR> 
Copyright &copy; 1997 Specialized Systems Consultants, Inc. </H5> 
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