Removing Empty Directories

We can remove empty directories inside a directory by using following command

$ ls -l * | grep -B1 "^total 0K" | grep -v -e "total 0K" -e "--" | cut -d: -f1 | xargs rmdir -v

The above command cannot delete recursively. Hence, using find command to delete recursively.

$ find . -type d -empty -delete

CPU Frequency Scaling

I have written a small shell script to increase or decrease CPU frequency. By default, it shows current CPU Frequency Scaling Governor. This can be changed only by root user. So this script needs to be run as root user or sudo as root, while changing the CPU Frequency Scaling governor.

#!/bin/bash

available_governors=$(cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_available_governors \
            | head -1 | sed -e 's/ \([a-zA-Z0-9]\)/|\1/g' -e 's/ $//')
if [ $# -ne 1 ]
then
  
   echo "USAGE: $0 [$available_governors]"
fi

echo "Command line to change CPU Scaling."
echo "                    - By Mitesh Singh Jat"
echo ""

## CPU Governor path
#/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
function current_cpu_governor ()
{
   echo -n "Current CPU Scaling Governor is: "
   cpu_scaling_governor="NOT SET"
   for governor in $(ls /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor)
   do
       cpu_scaling_governor=$(cat $governor)
   done
   echo "$cpu_scaling_governor"
}

current_cpu_governor;

## Exit, if no governor is provided
new_governor=""
if [ $# -eq 0 ]
then
   exit 0
else
   new_governor="$1"
fi

## Run as root always
user_id=`whoami`
if [[ "$user_id" != "root" ]]
then
   echo "$0: please run this script as root user."
   exit
fi 

if [ -z $(echo $available_governors | sed -e 's/^/|/' -e 's/$/|/' | grep "|$new_governor|") ]
then
   echo "Sorry, this mode '$new_governor' is not supported."
   exit 1
else
   echo "Setting CPU into '$new_governor' Mode..."
fi
## Now set cpu governor to the given mode
for governor in $(ls /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor)
do
   echo "$new_governor" > $governor
done
current_cpu_governor;

exit 0

Sample Run

Getting current CPU Frequency Scaling Governor
$ cd /path/where/cpu_scaling.sh/is/copied/
$ ./cpu_scaling.sh
USAGE: ./cpu_scaling.sh [powersave|conservative|ondemand|userspace|performance]
Command line to change CPU Scaling.
                   - By Mitesh Singh Jat

Current CPU Scaling Governor is: ondemand


Increasing CPU frequency (Please run as root).
$ ./cpu_scaling.sh performance
Command line to change CPU Scaling.
                   - By Mitesh Singh Jat

Current CPU Scaling Governor is: ondemand
./cpu_scaling.sh: please run this script as root user.
$ sudo ./cpu_scaling.sh performance
[sudo] password for mitesh:
Command line to change CPU Scaling.
                   - By Mitesh Singh Jat

Current CPU Scaling Governor is: ondemand
Setting CPU into Performance Mode...
Current CPU Scaling Governor is: performance
$ ./cpu_scaling.sh
USAGE: ./cpu_scaling.sh [powersave|conservative|ondemand|userspace|performance]
Command line to change CPU Scaling.
                   - By Mitesh Singh Jat

Current CPU Scaling Governor is: performance


Decreasing CPU frequency
$ sudo ./cpu_scaling.sh ondemand
Command line to change CPU Scaling.
                   - By Mitesh Singh Jat

Current CPU Scaling Governor is: performance
Setting CPU into OnDemand Mode...
Current CPU Scaling Governor is: ondemand

Find Files Created Between 2 Times

In order to find files created between two times (start hour and end hour). The required hours are hours from current time. For example,

Current time = 2 PM = 14:00

If you want file created between 9 AM and 12 PM today, the start hour and end hour are:

Start Hour = (14 - 9) = 5
End Hour = (14 - 12) = 2

Hence required command is:

$  ./find_files_between_times.pl /path/to/dir 5 2

The Perl script which does this is given below:-

#!/usr/bin/perl -w
#===============================================================================
#
#         FILE:  find_files_between_times.pl
#
#        USAGE:  ./find_files_between_times.pl <dir> <start_hour> <end_hour>
#
#  DESCRIPTION:  
#
#      OPTIONS:  ---
# REQUIREMENTS:  ---
#         BUGS:  ---
#        NOTES:  ---
#       AUTHOR:  Mitesh Singh Jat (mitesh), <mitesh[at]yahoo-inc[dot]com>
#      COMPANY:  Yahoo Inc, India
#      VERSION:  1.0
#      CREATED:  11/13/2009 10:00:02 PM IST
#     REVISION:  ---
#===============================================================================

use strict;
use warnings;

if (@ARGV != 3)
{
    print STDERR "Usage: $0 <dir> <start_hour> <end_hour>\n";
    exit(-1);
}

my $dir = $ARGV[0];
## Calculate current_hour - given_hour
#my $start_time = `/bin/date "+\%H"`;
my $start_time = $ARGV[1];
#chomp($start_time);
my $end_time = $ARGV[2];
$end_time = time - ($end_time * 60 * 60);
#$end_time = $start_time - $end_time;
#$start_time = $start_time - $ARGV[0];

if ($start_time > $end_time)
{
    ($start_time, $end_time) = ($end_time, $start_time);
}

my $cmd = "find $dir -ctime -$start_time";
print "Running $cmd\n";
my @files = `$cmd`;
foreach my $file (@files) # (`find $dir -ctime $start_time`)
{
    chomp($file);
    my ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
                           $atime,$mtime,$ctime,$blksize,$blocks) 
        = stat($file);

    if ($ctime > $end_time)
    {
        next;
    }
    print "$file\n";
}


exit(0);

Better Console Calculator Using bc

If we use expr for mathematical calculations on console (terminal), it is frustrating, and hard to remember syntax and escape sequences used in expr. :( This small tip will help us.

Just add following line in your .bashrc file (~/.bashrc).

function calc
{
echo "${1}" | bc -l;
}

Then update the shell environment by:

$ source ~/.bashrc

"calc" from the shell will work as follows:

$ calc 2+3
5
$ calc 1+2*3
7
$ calc 1.1*2
2.2
$ calc "(1+2)*3"
9
$ calc "(1+2)^3"
27
$ calc "s(.5)"
.47942553860420300027

Converting Improper mp3 into Proper mp3 for Nokia E71

The music player of Nokia E71 is vulnerable to improper mp3. It stucks forever, even if there is a single improper mp3. Improper mp3 is a mp3 file which does not conform to mp3 standard, there are some problem in mp3 headers. For more information on improper mp3, please read manual of checkmp3 command.

$ man checkmp3

I have written a shell script which converts improper mp3's into proper mp3.

#!/bin/bash

## Script to fix mp3 files using checkmp3

## Checking existance of checkmp3
checkmp3=`which checkmp3`

if [[ "$checkmp3" == "" ]]
then
    echo "$0: please install checkmp3."
    exit
fi

if [ $# -ne 1 ]
then
    echo "USAGE: $0 <mp3_file|dir_with_mp3s>"
    exit
fi

dir="$1"
file=""

if [[ -d "$dir" ]]
then
    echo "processing directory '$dir'"
    temp_file="$dir/fixed.mp3"
    for file in `find "$dir" -iname "*.mp3" | sed 's/ /\\\_/g'`
    do
        file=`echo "$file" | sed 's/\\\_/ /g'`
        echo "processing file '$file'"
        $checkmp3 -i -sf "$file" > "$temp_file"
        if [ $? -ne 0 ]
        then
            echo "$0: error in processing file '$file'"
        else 
            #eyeD3 "$temp_file"
            #$checkmp3 "$temp_file"
            mv "$temp_file" "$file"
        fi
    done
    rm -f "$temp_file"
else
    file="$dir"
    echo "processing file '$dir'"
    dir=`dirname "$file"`
    temp_file="$dir/fixed.mp3"
    echo "$temp_file"

    $checkmp3 -i -sf "$file" > "$temp_file"
    if [ $? -ne 0 ]
    then
        echo "$0: error in processing file '$file'"
    else 
        #eyeD3 "$temp_file"
        #$checkmp3 "$temp_file"
        mv "$temp_file" "$file"
    fi
fi
exit 0

Sample run:

$ ./fix_mp3.sh xyz.mp3
$ ./fix_mp3.sh /path/to/mp3/directory/

Disabling Macbook Pro Touchpad

We may want to disable Macbook Pro (or any other Laptop) Touchpad, such cases are:
(i) We have connected a USB mouse, so we do not want to use touchpad for now.
(ii) While typing, there is no use of touchpad, if touchpad is too sensitive, the cursor keeps on jumping due to slight touch of palm or finger.

I have written a script to disable/enable touchpad (which is using synaptics driver).






#!/bin/bash

## Disable touchpad if USB Mouse is attached

SYNAPTICS=`which synclient`

if [[ "$SYNAPTICS" == "" ]]
then
    echo "$0: please install synaptics touchpad driver."
    echo "Also make sure that 'Option         \"SHMConfig\" \"on\"'"
    echo " is added in Touchpad device Section in /etc/X11/xorg.conf"
    exit
fi

USB_mouse_present=`grep -ic "usb.*mouse" /proc/bus/input/devices`
# if no USB Mouse; enable touchpad
if [ $USB_mouse_present -eq 0 ]
then
    $SYNAPTICS TouchpadOff=0
else
    $SYNAPTICS TouchpadOff=1
fi 

# if any parameter [on|off] is given, override previous command
if [ $# -ge 1 ]
then
    if [ "$1" = "on" ]
    then
        $SYNAPTICS TouchpadOff=0
    else
        $SYNAPTICS TouchpadOff=1
    fi
fi

exit 0

Sample Run:
Turn on touchpad

$ ./touchpad.sh on

Turn off touchpad

$ ./touchpad.sh off

If we have plugged USB mouse, then just give following command

$ ./touchpad.sh

On removing USB mouse, give following, the touchpad will be enabled automatically. :)

$ ./touchpad.sh


PS: The configuration for synaptics driver can be referred from here or here.

IP Masquerade and Network Address Translation (NAT)

If we want to connect multiple computers to the Internet using single public IP Address, Masquerading (A form of NATing) helps us.

NAT describes the process of modifying the network addresses contained with datagram headers while they are in transit. IP masquerade is the name given to one type of network address translation that allows all of the hosts on a private network to use the Internet at the price of a single IP address.

IP masquerading allows you to use a private (reserved) IP network address on your LAN and have your Linux-based router perform some clever, real-time translation of IP addresses and ports. When it receives a datagram from a computer on the LAN, it takes note of the type of datagram it is, “TCP,” “UDP,” “ICMP,” etc., and modifies the datagram so that it looks like it was generated by the router machine itself (and remembers that it has done so). It then transmits the datagram onto the Internet with its single connected IP address. When the destination host receives this datagram, it believes the datagram has come from the routing host and sends any reply datagrams back to that address. When the Linux masquerade router receives a datagram from its Internet connection, it looks in its table of established masqueraded connections to see if this datagram actually belongs to a computer on the LAN, and if it does, it reverses the modification it did on the forward path and transmits the datagram to the LAN computer.

I have written a shell script, which converts a Linux box into a router. The script is written as:




#!/bin/bash

## Output interface: connected to Internet
out_iface=ppp0

## Run as root always
user_id=`whoami`

if [[ "$user_id" != "root" ]]
then
   echo "$0: please run this script as root user."
   exit
fi   

## Checking existance of iptables
IPTABLES=`which iptables`

if [[ "$IPTABLES" == "" ]]
then
   echo "$0: please install iptables."
   exit
fi   

if [ $# -ge 1 ]
then
   case "$1" in
       status)
           $IPTABLES -t nat -L
           exit 0
           ;;
       stop)
           ## Disabling Packet forwarding in kernel
           echo 0 > /proc/sys/net/ipv4/ip_forward
           echo "Flushing NAT MASQUERADE Entries"
           $IPTABLES -t nat -F
           exit 0
           ;;
       restart)
           $0 stop
           if [ $# -ge 2 ]
           then
               $0 start $2
           else   
               $0 start
           fi   
           ;;
       start)
           if [ $# -ge 2 ]
           then
               out_iface=$2
           fi   
           ## Enabling Packet forwarding in kernel
           echo 1 > /proc/sys/net/ipv4/ip_forward

           ## Enabling NAT Masquerade, if not enabled
           if [ -z "`$IPTABLES -t nat -L | grep MASQUERADE`" ]
           then
              
               $IPTABLES -t nat -A POSTROUTING -o $out_iface -j MASQUERADE
           fi   
           ;;
       *)
           echo "USAGE: $0 <start|status|restart|stop> [internet_interface]"
           exit 1
           ;;
esac           
else   
   echo "USAGE: $0 <start|status|restart|stop> [internet_interface]"
   exit 1
fi   

exit 0

Sample Runs:

$ ./NAT_Masquerade.sh
./NAT_Masquerade.sh: please run this script as root user.
$ sudo ./NAT_Masquerade.sh
USAGE: ./NAT_Masquerade.sh [internet_interface]
$
Here, internet_interface is the interface which is connected to internet.
By default, ppp0 (Dial up) interface is taken.

$ sudo ./NAT_Masquerade.sh status
Chain PREROUTING (policy ACCEPT)
target prot opt source destination

Chain POSTROUTING (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination
$
Since Masquerade is not yet applied, Chain POSTROUTING rule is empty.

Applying IP Masquerade to internet_interface eth0.
$ sudo ./NAT_Masquerade.sh start eth0
$ sudo ./NAT_Masquerade.sh status
Chain PREROUTING (policy ACCEPT)
target prot opt source destination

Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
MASQUERADE all -- anywhere anywhere

Chain OUTPUT (policy ACCEPT)
target prot opt source destination
$ sudo ./NAT_Masquerade.sh stop
Flushing NAT MASQUERADE Entries
$



Determining Bits of CPU and OS (32/64-bits)

In order to determine whether OS/CPU is 32-bit or 64-bit,
you can use this shell script.

#!/bin/bash
echo -n "Running "

RES=`uname -a | grep 64`
if [ $? -eq 0 ]; then

    echo -n "64-bit "
else
    echo -n "32-bit "
fi
echo -n "operating system on a "

RES=`cat /proc/cpuinfo | grep " lm "`
if [ $? -eq 0 ]; then

    echo -n "64-bit "
else
    echo -n "32-bit "
fi
echo "machine"

Sample Run:

$ ./os_cpu.sh
Running 64-bit operating system on a 64-bit machine

Web Access through Proxy Server by Terminal Applications

In many companies/Universities, the web access is granted through Proxy Server (Usually SQUID; hence port 3128).
There are many terminal applications (run on command line interface), which access Internet/Web. For example:
wget (to download file), ftp, lynx/links (to access website), apt/yum (to download and install package). If we are behind
proxy, these applications do not work. The easy solution is to set some shell environment variables, explained below:

For accessing web(lynx/links) using a non-authenticated proxy:
$ export http_proxy="http://proxy.yourcompany.com:3128"

Verify that the setting took place
$ echo $http_proxy
http://proxy.yourcompany.com:3128

For accessing web(lynx/links) using a authenticated proxy:
$ export http_proxy="http://username:password@proxy.yourcompany.com:3128"

If you want the change to be permanent (there each time you open a terminal),
add the export line to .bashrc in your 'home' directory.
$ echo 'export http_proxy="http://proxy.yourcompany.com:3128"'″ >> ~/.bashrc

Secure HTTP (over SSL) access
$ export https_proxy="https://proxy.yourcompany.com:3128"

FTP access
$ export ftp_proxy="ftp://proxy.yourcompany.com:3128"

Terminating Processes Containing Given Pattern

Generally, if you want to terminate a process which contains the given pattern, you use following 4 steps:

1. $ ps aux | grep pattern 
2. Copy the pid of the process from output of above command.
3. Paste this pid in the following command
4. $ kill -9 pid

The above procedure is cumbersome and requires much typing.

Therefore I have written a program to terminate process(es), which contains given pattern. (I am assuming that ~/bin is in your $PATH).

$ vi ~/bin/kill_prog.sh

#!/bin/sh

# Kills the program given

if [ $# -lt 2 ]
then
  echo "Usage: $0 [1/0] signal program-name"
  echo "[0/1] Do not Kill / Do kill (optional)"
  echo "signal -TERM (Graceful Terminate), -KILL (Abrupt KIll)"
  exit
fi

donothing=1
signal=$1
program=$2
if [ $# -gt 2 ]
then
  donothing=$1
  signal=$2
  program=$3
fi

pids=$(ps auxww | awk "/ $program / { print \$2 }")


for pid in $pids
do
  if [ $donothing -eq 1 ] ; then
  echo "kill $signal $pid"
  else
  kill $signal $pid
  fi
done

#end kill_prog.sh

By default, this program does not kills the process. You have to

pass 0 as second parameter to the command to kill.

Sample runs of above programs:

$ kill_prog.sh
Usage: /home/mitesh/Programming/Shell/WCS/kill_prog.sh [1/0] signal program-name
[0/1] Do not Kill / Do kill (optional)
signal -TERM (Graceful Terminate), -KILL (Abrupt KIll)
$ kill_prog.sh -TERM ping
kill -TERM 16050
$ kill_prog.sh -KILL ping
kill -KILL 16050
$ kill_prog.sh 1 -KILL ping
kill -KILL 16050
$ kill_prog.sh 0 -KILL ping
Killed

The last command actually terminates(-TERM) or kills(-TERM).

Shell Session Recording

In order to record the commands and their output in a shell session,
you can use script command. For example:

[mitesh@linuxbox:370:~]$ script
Script started, file is typescript
[mitesh@linuxbox:370:~]$ ls
CvsRoot Desktop Documents Download Examples linux Music PDF Pictures Programming Public Templates typescript Videos workspace
[mitesh@linuxbox:371:~]$ /bin/date
Fri Oct 3 16:51:42 IST 2008
[mitesh@linuxbox:372:~]$ whoami
mitesh
[mitesh@linuxbox:373:~]$ exit
exit

Script done, file is typescript

You can view the output file typescript file using your favorite editor.
$ cat typescript
Script started on Friday 03 October 2008 04:51:27 PM IST
[mitesh@linuxbox:370:~]$ ls
CvsRoot Desktop Documents Download Examples linux Music PDF Pictures Programming Public Templates typescript Videos workspace
[mitesh@linuxbox:371:~]$ /bin/date
Fri Oct 3 16:51:42 IST 2008
[mitesh@linuxbox:372:~]$ whoami
mitesh
[mitesh@linuxbox:373:~]$ exit
exit

Script done on Friday 03 October 2008 04:51:54 PM IST

PS: you can save the output to any file, you want instead of typescript in
current directory. For example
$ script shell_session_20081003.log
...
...
$ exit
$ cat shell_session_20081003.log