Tuesday, 21 February 2012

10 Tools To Spice Your UNIX Shell Scripts

There are some misconceptions that shell scripts are only for a CLI environment. You can easily use various tools to write GUI and/or network (socket) scripts under KDE or Gnome desktops. Shell scripts can make use of some of the GUI widget (menus, warning boxs, progress bars etc). You can always control the final output, cursor position on screen, various output effects, and so on. With the following tools you can build powerful, interactive, user friendly UNIX / Linux bash shell scripts.
#1: notify-send Command
Creating GUI application is not just expensive task but task that takes time and patience. Luckily, both UNIX and Linux ships with plenty of tools to write beautiful GUI scripts. The following tools are tested on FreeBSD and Linux operating systems but should work under other UNIX like operating systems.
The notify-send command allows you to send desktop notifications to the user via a notification daemon from the command line. This is useful to inform the desktop user about an event or display some form of information without getting in the user's way. You need to install the following package:
$ sudo apt-get install libnotify-binIn this example, send simple desktop notification from the command line, enter:
notify-send "rsnapshot done :)"
Sample outputs:
Fig:01: notify-send in action
Fig:01: notify-send in action
Here is another code with additional options:
live=$(lynx --dump http://money.rediff.com/ | grep 'BSE LIVE' | awk '{ print $5}' | sed 's/,//g;s/\.[0-9]*//g')
[ $notify_counter -eq 0 ] && [ $live -ge $alert ] && { notify-send -t 5000 -u low -i   "BSE Sensex touched 18k";  notify_counter=1; }
Sample outputs:
Fig.02: notify-send with timeouts and other options
Fig.02: notify-send with timeouts and other options
  • -t 5000: Specifies the timeout in milliseconds ( 5000 milliseconds = 5 seconds)
  • -u low : Set the urgency level (i.e. low, normal, or critical).
  • -i gtk-dialog-info : Set an icon filename or stock icon to display (you can set path as -i /path/to/your-icon.png).
For more information on use of the notify-send utility, please refer to the notify-send man page, viewable by typing man notify-send from the command line:
man notify-send

#2: tput Command

The tput command is used to set terminal features. With tput you can set:
  • Move the cursor around the screen.
  • Get information about terminal.
  • Set colors (background and foreground).
  • Set bold mode.
  • Set reverse mode and much more.
Here is a sample code:
# clear the screen
tput clear
# Move cursor to screen location X,Y (top left is 0,0)
tput cup 3 15
# Set a foreground colour using ANSI escape
tput setaf 3
echo "XYX Corp LTD."
tput sgr0
tput cup 5 17
# Set reverse video mode
tput rev
echo "M A I N - M E N U"
tput sgr0
tput cup 7 15
echo "1. User Management"
tput cup 8 15
echo "2. Service Management"
tput cup 9 15
echo "3. Process Management"
tput cup 10 15
echo "4. Backup"
# Set bold mode
tput bold
tput cup 12 15
read -p "Enter your choice [1-4] " choice
tput clear
tput sgr0
tput rc
Sample outputs:
Fig.03: tput in action
Fig.03: tput in action

For more detail concerning the tput command, see the following man page:
man 5 terminfo
man tput

#3: setleds Command

The setleds command allows you to set the keyboard leds. In this example, set NumLock on:
setleds -D +num
To turn it off NumLock, enter:
setleds -D -num
  • -caps : Clear CapsLock.
  • +caps : Set CapsLock.
  • -scroll : Clear ScrollLock.
  • +scroll : Set ScrollLock.
See setleds command man page for more information and options:
man setleds

#4: zenity Command

The zenity commadn will display GTK+ dialogs box, and return the users input. This allows you to present information, and ask for information from the user, from all manner of shell scripts. Here is a sample GUI client for the whois directory service for given domain name:
# Get domain name
domain=$(${_zenity} --title  "Enter domain" \
	            --entry --text "Enter the domain you would like to see whois info" )
if [ $? -eq 0 ]
  # Display a progress dialog while searching whois database
  whois $domain  | tee >(${_zenity} --width=200 --height=100 \
  				    --title="whois" --progress \
			            --pulsate --text="Searching domain info..." \
                                    --auto-kill --auto-close \
                                    --percentage=10) >${_out}
  # Display back output
  ${_zenity} --width=800 --height=600  \
	     --title "Whois info for $domain" \
	     --text-info --filename="${_out}"
  ${_zenity} --error \
	     --text="No input provided"
Sample outputs:
Fig.04: zenity in Action
Fig.04: zenity in Action

See the zenity man page for more information and all other supports GTK+ widgets:
zenity --help
man zenity

#5: kdialog Command

kdialog is just like zenity but it is designed for KDE desktop / qt apps. You can display dialogs using kdialog. The following will display message on screen:
kdialog --dontagain myscript:nofilemsg --msgbox "File: '~/.backup/config' not found."
Sample outputs:
Fig.05: Suppressing the display of a dialog
Fig.05: Suppressing the display of a dialog
See shell scripting with KDE Dialogs tutorial for more information.

#6: Dialog

Dialog is an application used in shell scripts which displays text user interface widgets. It uses the curses or ncurses library. Here is a sample code:
dialog --title "Delete file" \
--backtitle "Linux Shell Script Tutorial Example" \
--yesno "Are you sure you want to permanently delete \"/tmp/foo.txt\"?" 7 60
# Get exit status
# 0 means user hit [yes] button.
# 1 means user hit [no] button.
# 255 means user hit [Esc] key.
case $response in
   0) echo "File deleted.";;
   1) echo "File not deleted.";;
   255) echo "[ESC] key pressed.";;
See the dialog man page for details:
man dialog

A Note About Other User Interface Widgets Tools

UNIX and Linux comes with lots of other tools to display and control apps from the command line, and shell scripts can make use of some of the KDE / Gnome / X widget set:
  • gmessage - a GTK-based xmessage clone.
  • xmessage - display a message or query in a window (X-based /bin/echo)
  • whiptail - display dialog boxes from shell scripts
  • python-dialog - Python module for making simple Text/Console-mode user interfaces

#7: logger command

The logger command writes entries in the system log file such as /var/log/messages. It provides a shell command interface to the syslog system log module:
logger "MySQL database backup failed."
tail -f /var/log/messages
logger -t mysqld -p daemon.error "Database Server failed"
tail -f /var/log/syslog
Sample outputs:
Apr 20 00:11:45 vivek-desktop kernel: [38600.515354] CPU0: Temperature/speed normal
Apr 20 00:12:20 vivek-desktop mysqld: Database Server failed
See howto write message to a syslog / log file for more information. Alternatively, you can see the logger man page for details:
man logger

#8: setterm Command

The setterm command can set various terminal attributes. In this example, force screen to turn black in 15 minutes. Monitor standby will occur at 60 minutes:
setterm -blank 15 -powersave powerdown -powerdown 60
In this example show underlined text for xterm window:
setterm -underline on;
echo "Add Your Important Message Here"
setterm -underline off
Another useful option is to turn on or off cursor:
setterm -cursor off
Turn it on:
setterm -cursor on
See the setterm command man page for details:
man setterm

#9: smbclient: Sending Messages To MS-Windows Workstations

The smbclient command can talk to an SMB/CIFS server. It can send a message to selected users or all users on MS-Windows systems:
smbclient -M WinXPPro <1
Message 2
echo "${Message}" | smbclient -M salesguy2
See smbclient man page or read our previous post about "sending a message to Windows Workstation" with smbclient command:
man smbclient

#10: Bash Socket Programming

Under bash you can open a socket to pass some data through it. You don't have to use curl or lynx commands to just grab data from remote server. Bash comes with two special device files which can be used to open network sockets. From the bash man page:
  1. /dev/tcp/host/port - If host is a valid hostname or Internet address, and port is an integer port number or service name, bash attempts to open a TCP connection to the corresponding socket.
  2. /dev/udp/host/port - If host is a valid hostname or Internet address, and port is an integer port number or service name, bash attempts to open a UDP connection to the corresponding socket.
You can use this technquie to dermine if port is open or closed on local or remote server without using nmap or other port scanner:
# find out if TCP port 25 open or not
(echo >/dev/tcp/localhost/25) &>/dev/null && echo "TCP port 25 open" || echo "TCP port 25 close"
You can use bash loop and find out open ports with the snippets:
echo "Scanning TCP ports..."
for p in {1..1023}
  (echo >/dev/tcp/localhost/$p) >/dev/null 2>&1 && echo "$p open"
Sample outputs:
Scanning TCP ports...
22 open
53 open
80 open
139 open
445 open
631 open
In this example, your bash script act as an HTTP client:
exec 3<> /dev/tcp/${1:-www.cyberciti.biz}/80
printf "GET / HTTP/1.0\r\n" >&3
printf "Accept: text/html, text/plain\r\n" >&3
printf "Accept-Language: en\r\n" >&3
printf "User-Agent: nixCraft_BashScript v.%s\r\n" "${BASH_VERSION}"   >&3
printf "\r\n" >&3
while read LINE <&3
   # do something on $LINE
   # or send $LINE to grep or awk for grabbing data
   # or simply display back data with echo command
   echo $LINE
See the bash man page for more information:
man bash

A Note About GUI Tools and Cronjob

You need to request local display/input service using export DISPLAY=[user's machine]:0 command if you are using cronjob to call your scripts. For example, call /home/vivek/scripts/monitor.stock.sh as follows which uses zenity tool:
@hourly DISPLAY=:0.0 /home/vivek/scripts/monitor.stock.sh

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