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sources/tech/Bash Getopts--Scripts with Command Line Options.md
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Bash Getopts – Scripts with Command Line Options
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================================================================================
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I've always wanted to know how to create command line options for my Bash scripts. After some research I found there are two functions available to handle this; **getopt** and **getopts**. I'm not going to get into the debate about which one is better. **getopts** is a shell builtin and seems a little easier to implement than **getopt**, so I'll go with that for now.
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### bash getopts ###
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I started out just trying to figure out how to process command line switches in my scripts. Eventually, I added some other useful functionality that makes this a good starting template for any interactive script. I've also included a help function with text formatting to make it a little easier to read.
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Rather than go into a lengthy explanation of how **getopts** works in **bash**, I think it's simpler to just show some working code in a script.
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#!/bin/bash
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######################################################################
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#This is an example of using getopts in Bash. It also contains some
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#other bits of code I find useful.
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#Author: Linerd
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#Website: http://tuxtweaks.com/
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#Copyright 2014
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#License: Creative Commons Attribution-ShareAlike 4.0
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#http://creativecommons.org/licenses/by-sa/4.0/legalcode
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######################################################################
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#Set Script Name variable
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SCRIPT=`basename ${BASH_SOURCE[0]}`
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#Initialize variables to default values.
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OPT_A=A
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OPT_B=B
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OPT_C=C
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OPT_D=D
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#Set fonts for Help.
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NORM=`tput sgr0`
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BOLD=`tput bold`
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REV=`tput smso`
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#Help function
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function HELP {
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echo -e \\n"Help documentation for ${BOLD}${SCRIPT}.${NORM}"\\n
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echo -e "${REV}Basic usage:${NORM} ${BOLD}$SCRIPT file.ext${NORM}"\\n
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echo "Command line switches are optional. The following switches are recognized."
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echo "${REV}-a${NORM} --Sets the value for option ${BOLD}a${NORM}. Default is ${BOLD}A${NORM}."
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echo "${REV}-b${NORM} --Sets the value for option ${BOLD}b${NORM}. Default is ${BOLD}B${NORM}."
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echo "${REV}-c${NORM} --Sets the value for option ${BOLD}c${NORM}. Default is ${BOLD}C${NORM}."
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echo "${REV}-d${NORM} --Sets the value for option ${BOLD}d${NORM}. Default is ${BOLD}D${NORM}."
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echo -e "${REV}-h${NORM} --Displays this help message. No further functions are performed."\\n
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echo -e "Example: ${BOLD}$SCRIPT -a foo -b man -c chu -d bar file.ext${NORM}"\\n
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exit 1
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}
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#Check the number of arguments. If none are passed, print help and exit.
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NUMARGS=$#
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echo -e \\n"Number of arguments: $NUMARGS"
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if [ $NUMARGS -eq 0 ]; then
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HELP
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fi
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### Start getopts code ###
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#Parse command line flags
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#If an option should be followed by an argument, it should be followed by a ":".
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#Notice there is no ":" after "h". The leading ":" suppresses error messages from
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#getopts. This is required to get my unrecognized option code to work.
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while getopts :a:b:c:d:h FLAG; do
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case $FLAG in
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a) #set option "a"
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OPT_A=$OPTARG
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echo "-a used: $OPTARG"
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echo "OPT_A = $OPT_A"
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;;
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b) #set option "b"
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OPT_B=$OPTARG
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echo "-b used: $OPTARG"
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echo "OPT_B = $OPT_B"
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;;
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c) #set option "c"
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OPT_C=$OPTARG
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echo "-c used: $OPTARG"
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echo "OPT_C = $OPT_C"
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;;
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d) #set option "d"
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OPT_D=$OPTARG
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echo "-d used: $OPTARG"
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echo "OPT_D = $OPT_D"
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;;
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h) #show help
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HELP
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;;
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\?) #unrecognized option - show help
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echo -e \\n"Option -${BOLD}$OPTARG${NORM} not allowed."
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HELP
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#If you just want to display a simple error message instead of the full
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#help, remove the 2 lines above and uncomment the 2 lines below.
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#echo -e "Use ${BOLD}$SCRIPT -h${NORM} to see the help documentation."\\n
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#exit 2
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;;
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esac
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done
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shift $((OPTIND-1)) #This tells getopts to move on to the next argument.
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### End getopts code ###
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### Main loop to process files ###
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#This is where your main file processing will take place. This example is just
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#printing the files and extensions to the terminal. You should place any other
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#file processing tasks within the while-do loop.
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while [ $# -ne 0 ]; do
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FILE=$1
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TEMPFILE=`basename $FILE`
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#TEMPFILE="${FILE##*/}" #This is another way to get the base file name.
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FILE_BASE=`echo "${TEMPFILE%.*}"` #file without extension
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FILE_EXT="${TEMPFILE##*.}" #file extension
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echo -e \\n"Input file is: $FILE"
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echo "File withouth extension is: $FILE_BASE"
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echo -e "File extension is: $FILE_EXT"\\n
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shift #Move on to next input file.
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done
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### End main loop ###
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exit 0
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Paste the above text into a text editor and then save it somewhere in your executable path. I chose to call the script **options** and I saved it under **/home/linerd/bin**. Once you save it, make sure to make it executable.
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chmod +x ~/bin/options
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Now you can run the script. Try running it with the **-h** switch to show the help information.
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options -h
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Now try running it with an unsupported option.
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options -z
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Finally, getopts can handle your command line options in any order. The only rule is that the file or files you are processing have to come after all of the option switches.
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options -d bar -c chu -b man -a foo example1.txt example2.txt
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So you can see from these examples how you can set variables in your scripts with command line options. There's more going on than just getopts in this script, but I think these are valuable additions that make this a good starting template for new scripts. If you'd like to learn more about bash getopts, you can find the documentation buried deep within the bash man page in the "Builtins" section. You can also find info in the [Bash Reference Manual][1].
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### What Next? ###
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So what will you use getopts for? Let me know in the comments.
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--------------------------------------------------------------------------------
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via: http://tuxtweaks.com/2014/05/bash-getopts/
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译者：[译者ID](https://github.com/译者ID) 校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
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[1]:http://tuxtweaks.com/2014/05/bash-getopts/www.gnu.org/software/bash/manual/html_node/Bourne-Shell-Builtins.html
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How to take a screenshot from the command line on Linux
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================================================================================
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There are various flavors of Linux screenshot utilities, including desktop-specific screenshot programs (e.g., KSnapshot for KDE, gnome-screenshot for GNOME, Screenshooter for Xfce), or general screenshot utilities (e.g., Shutter). One of unique screenshot utilities is Scrot (short for "SCReen shOT"), which is a **command-line screenshot utility**. While its interface is minimalistic, Scrot is, feature-wise, as powerful as other dedicated GUI-based screen capture tools. For example, Scrot supports delayed screenshot, adjustable quality/size, command line pipelining, etc. If you are one of those command line junkies, Scrot is a useful tool to add to your arsenal. In this tutorial, I will describe **how to take a screenshot from the command line with Scrot**.
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### Install Scrot on Linux ###
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To install Scrot on Debian, Ubuntu or Linux Mint:
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$ sudo apt-get install scrot
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To install Scrot on Fedora:
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$ sudo yum install scrot
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To install Scrot on CentOS, you can build it from its source as follows.
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First [enable Repoforge on CentOS][1], and use the following commands.
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$ sudo yum install giblib-devel
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$ wget http://linuxbrit.co.uk/downloads/scrot-0.8.tar.gz
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$ tar xvfvz scrot-0.8.tar.gz
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$ cd scrot-0.8
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$ ./configure
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$ make
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$ sudo make install
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### Take Screenshots with Scrot ###
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In the rest of the tutorial, I will describe how to use Scrot to take screenshots in various ways.
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#### 1. Take a screenshot of the entire desktop ####
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Screen-capturing the entire desktop is easy. Simply run Scrot command without any argument, and it will save a screenshot of the entire desktop as a (date-stamped) .png file in the current directory.
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$ scrot
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You can also specify a destination folder and image file name.
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$ scrot ~/Pictures/my_desktop.png
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#### 2. Take a screenshot of a particular window or a rectangular region ####
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Scrot allows you to choose a specific window or define a rectangular region in your desktop to take a screenshot of. For that, use the following command.
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$ scrot -s
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After running this command, go ahead and click on any window or draw a rectangle with your mouse, which will trigger screen capture of the selected window/region.
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Sometimes the chosen region or window may be partially blocked by other windows of the desktop. In that case, you need some time to clear the area before taking a shot. That is when "delayed" screenshot can help you, as described next.
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#### 3. Take a delayed screenshot ####
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Delayed capture can be useful under various circumstances. Right before taking a shot, you may want to move windows around, activate a menu, or trigger a certain event (e.g., notification), etc. With "-d N" option, we can delay a screenshot process by N seconds.
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$ scrot -s -d 5
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#### 4. Adjust quality of a screenshot ####
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You can adjust the image quality of a screenshot in the range of 1 to 100 (the higher the better quality). Default quality is 75.
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$ scrot -q 50
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#### 5. Adjust the size of a screenshot ####
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You can adjust the size of a screenshot in the range of 1 to 100 (the higher the bigger). To reduce screenshot size to 10% of the original:
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$ scrot -t 10
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#### 6. Pipeline a captured screenshot to another command ####
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Scrot allows you to send a saved screenshot image to any arbitrary command as an input. This option can be useful when you want to do any post-processing on a screenshot image. The filename/path of a screenshot is stored as "$f" string.
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$ scrot -e 'mv $f ~/screenshots'
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--------------------------------------------------------------------------------
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via: http://xmodulo.com/2014/05/take-screenshot-command-line-linux.html
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译者：[译者ID](https://github.com/译者ID) 校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创翻译，[Linux中国](http://linux.cn/) 荣誉推出
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[1]:http://xmodulo.com/2013/01/how-to-set-up-rpmforge-repoforge-repository-on-centos.html
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