I wrote a bash script as below:
#!/bin/bash
echo "Enter a file name"
read filename
import -window root $HOME/Desktop/$filename.png
I expected this script to take a screen shot and save the image with the given filename on my desktop.
Problem: My Ubuntu terminal is giving error:
import: Command Not Found
You need to install the package imagemagic to use import command, via Ubuntu Software Center or:
sudo apt-get install imagemagick
This will allow you to use import command. Also try out graphicsmagick-imagemagick-compat package.
other alternatives to import are
scrot. Install it with:
sudo aptitude install scrot
Usage: scrot screen.png
gnome-screenshot. Install it with:
sudo aptitude install gnome-screenshot
You can use the best screenshot tool
shutter 
for use in scripts too! And I believe, this is the most powerful tool and give you most advanced and fine-tuned options to use in scripts.
Install it with the command in a terminal
sudo apt-get install shutter
or using the software center (by clicking the big button below)
And after installation, use this command to take a screenshot of the whole display and save the screenshot in a file named, myshot.png
shutter -f -o myshot.png -e
The -f tells shutter to take a screenshot of the whole display. You could also use -a to take a screenshot of the active window, or tell it to take a shot from any specific window.
The -o option is used for telling shutter the output file name. You could specify any file name
The e option causes shutter to exit after taking the screenshot.
The output of shutter --help is given below for reference.
Usage:
shutter [options]
Options:
Example 1
shutter -a -p=myprofile --min_at_startup
Example 2
shutter -s=100,100,300,300 -e
Example 3
shutter --window=.*firefox.*
Example 4
shutter --web=http://shutter-project.org/ -e
Capture Mode Options:
-s, --select=[X,Y,WIDTH,HEIGHT]
Capture an area of the screen. Providing X,Y,WIDTH,HEIGHT is
optional.
-f, --full
Capture the entire screen.
-w, --window=[NAME_PATTERN]
Select a window to capture. Providing a NAME_PATTERN (Perl-style
regex) ist optional.
-a, --active
Capture the current active window.
--section
Capture a section. You will be able to select any child window
by moving the mouse over it.
-m, --menu
Capture a menu.
-t, --tooltip
Capture a tooltip.
--web=[URL]
Capture a webpage. Providing an URL ist optional.
-r, --redo
Redo last screenshot.
Settings Options:
-p, --profile=NAME
Load a specific profile on startup.
-o, --output=FILENAME
Specify a filename to save the screenshot to (overwrites any
profile-related setting).
Supported image formats: You can save to any popular image
format (e.g. jpeg, png, gif, bmp). Additionally it is possible
to save to pdf, ps or svg.
Please note: There are several wildcards available, like
%Y = year
%m = month
%d = day
%T = time
$w = width
$h = height
$name = multi-purpose (e.g. window title)
$nb_name = like $name but without blanks in resulting strings
$profile = name of current profile
$R = random char (e.g. $RRRR = ag4r)
%NN = counter
The string is interpretted by strftime. See "man strftime" for
more examples.
As an example: shutter -f -e -o './%y-%m-%d_$w_$h.png' would
create a file named '11-10-28_1280_800.png' in the current
directory.
Application Options:
-h, --help
Prints a brief help message and exits.
-v, --version
Prints version information.
-d, --debug
Prints a lot of debugging information to STDOUT.
--clear_cache
Clears cache, e.g. installed plugins, at startup.
--min_at_startup
Starts Shutter minimized to tray.
--disable_systray
Disables systray icon.
-e, --exit_after_capture
Exit after the first capture has been made. This is useful when
using Shutter in scripts.
To install imagemagick, containing the program import, see the other answer. However, you can also launch gnome-screenshot from command line by calling gnome-screenshot. The applet will take the screenshot without delay and show a dialog to enter a file name:
I like scrot for this (apt install scrot):
#!/bin/bash
scrot -u -q 100 '/home/stephen/pic/screenshots/screenshot.%Y%m%d_%H%M%S.png'
And linked to some key. I ran into issues using the printscr key and didn't care enough to investigate.
