Difference between pages "BaBE - Bash By Examples" and "Set up a Webcam with Linux"

From Linuxintro
(Difference between pages)
 
 
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<metadesc>BaBE - Bash by Examples; Your significant Linux scripting tutorial: Redirection, Piping, conditional execution, user dialogs, loops, process management, backticks, string replacement, pitfalls and much more.</metadesc>
+
<metadesc>Here is how you set up your webcam with Linux, capture videos and images, do VoIP calls and automate recording. Tested with SUSE Linux, Ubuntu and Debian.</metadesc>
 +
[[File:Screenshot_from_2020-03-01_13-18-32.png]]
 +
You want to set up your webcam with Linux, see a video stream from it and learn which applications you can use with it, right? Then this article is for you.
  
−
BaBE - Bash By Examples; Your significant Linux scripting tutorial;;
+
= Try it =
 +
First let's try if it works out of the box, so, connect your webcam (if it's not inbuilt), [[open a terminal]] and start the application '''''cheese''''':
 +
cheese
  
−
<pic src="http://www.linuxintro.org/images/Bash-scripting-mindmap.jpg" width=70% align=right caption=MindMap />
+
This should switch on your webcam and you should see what it's recording.  
  
−
= Hello world =
+
Ok, you are reading on, so there is still something left, maybe:
−
The easiest way to get your feet wet with a programming language is to start with a program that simply outputs a trivial text, the so-called hello-world-example. Here it is for bash:
+
* terminal says "command not found", you need to install cheese. Read on at [[#Install_cheese|Install Cheese]].
−
* create a file named hello in your home directory with the following content:
+
* cheese does not show the camera's content -> read on at [[#Check the Setup|Check the Setup]].
−
#!/bin/bash
+
* you want to [[#record_a_video]] with your webcam.
−
echo "Hello, world!"
 
−
* [[open a console]], make the file executable:
 
−
chmod +x hello
 
−
* now you can execute your file like this:
 
−
./hello
 
−
Hello, world!
 
−
* or like this:
 
−
bash hello
 
−
Hello, world!
 
−
You see - the output of your shell [[program]] is the same as if you had entered the commands into a console.
 
  
−
= calling commands =
+
= Install cheese =  
−
In your shell script you can call every command that you can call when [[opening a console]]:
+
To install cheese, you need to know your distribution. Here is how to [[find out your distribution]].
−
<source>
+
* for Debian, Raspbian, Ubuntu, Kubuntu, Flubuntu, Xubuntu, GEUbuntu, Edubuntu, ...:
−
echo "This is a directory listing, latest modified files at the bottom:"
+
  sudo apt-get install cheese
−
ls -ltr
+
* for SUSE:
−
echo "Now calling a browser"
+
  yast -i cheese
−
firefox
 
−
echo "Continuing with the script"
 
−
</source>
 
−
 
 
−
= variables =
 
−
== input ==
 
−
To show you how to deal with variables, we will now write a script that asks for your name and greets you:
 
−
<source>
 
−
echo "what is your name? "
 
−
read name
 
−
echo "hello $name"
 
−
</source>
 
−
You see that the name is stored in a variable $name. Note the quotation marks '''"''' around "hello $name". By using these you say that you want variables to be replaced by their content. If you were to use apostrophes, the name would not be printed, but $name instead.
 
−
 
 
−
== ${} ==
 
−
The ${} operator stands for the variable, there is no difference if you write
 
−
echo "$name"
 
−
or
 
−
echo "${name}"
 
−
So what is the sense of this? Imagine you want to echo a string directly, without any blank, after the content of a variable:
 
−
<source>
 
−
echo "if I add the syllable owa to your name it will be ${name}owa"
 
−
</source>
 
−
 
 
−
== common mistakes ==
 
−
Note that the variable is called $name, however the correct statement to read it from the keyboard is
 
−
read name
 
−
It is a common mistake to write
 
−
read $name
 
−
which means "read a string and store it into the variable whose name is stored in $name"
 
−
 
 
−
= parameters =
 
−
<source>
 
−
echo "Here are all parameters you called this script with: $@"
 
−
echo "Here is parameter 1: $1"
 
−
echo "Which parameter do you want to be shown? "
 
−
read number
 
−
args=("$@")
 
−
echo "${args[$number-1]}"
 
−
</source>
 
−
 
 
−
= return codes =
 
−
Every bash script can communicate with the rest of the system by
 
−
* sending data to [[stdout]]
 
−
* sending data to [[stderr]]
 
−
* delivering a return code
 
−
The return code is 0 if everything worked well. You can query it for the most recent command using $?:
 
−
<source>
 
−
bootstick@bootstick:~$ echo "hello world"; echo $?
 
−
hello world
 
−
0
 
−
bootstick@bootstick:~$ echo "hello world">/proc/cmdline; echo $?
 
−
bash: /proc/cmdline: Permission denied
 
−
1
 
−
</source>
 
−
 
 
−
In bash, true is 0 and false is any value but 0. There exist two commands, true and false that deliver true or false, respectively:
 
−
bootstick@bootstick:~$ true; echo $?
 
−
0
 
−
bootstick@bootstick:~$ false; echo $?
 
−
1
 
−
 
 
−
= line feeds =
 
−
In bash you can use line feeds or semicolons to separate commands. For example:
 
−
<source>
 
−
read name
 
−
if [ $name = "Thorsten" ]; then echo "I know you"; fi
 
−
</source>
 
−
Instead of a semicolon you can write a line feed like this:
 
−
<source>
 
−
read name
 
−
if [ $name = "Thorsten" ]
 
−
  then echo "I know you"
 
−
fi
 
−
</source>
 
−
 
 
−
So we could put everything into one line and separate the commands by semicolons:
 
−
<source>
 
−
read name; if [ $name = "Thorsten" ]; then echo "I know you"; fi
 
−
</source>
 
−
 
 
−
If you want to insert a line feed where you do not need one, e.g. to make the code better readable, just put a backslash at the line's end to indicate it will continue:
 
−
<source>
 
−
read \
 
−
  name
 
−
if [ $name = "Thorsten" ]
 
−
  then \
 
−
    echo "I know you"
 
−
fi
 
−
</source>
 
−
 
 
−
= storing a command's output =
 
−
To read a command's output into a variable use $(), backticks or [[piping]].
 
−
 
 
−
== $() ==
 
−
arch=$(uname -m)
 
−
echo "Your system is a $arch system."
 
−
 
 
−
== backticks ==
 
−
arch=`uname -m`
 
−
echo "Your system is a $arch system."
 
−
 
 
−
== piping ==
 
−
[[Piping]] is a very elegant concept in the Linux world. It allows you to take one command's output and use it as input for the next command. Now you can divide tasks into smaller tasks. For example instead of having a program counting all files in a directory you use one program (ls) to ''list'' all files in a directory and one program (wc) to count the lines:
 
−
<source>
 
−
ls | wc -l
 
−
</source>
 
−
You can also put the output into a variable, in this case $arch:
 
−
<source>
 
−
  uname -m | while read arch; do echo "Your system is a $arch system."; done
 
−
</source>
 
−
 
 
−
== comparison ==
 
−
The advantage of using backticks over $() is that backticks also work in the sh shell. The advantage of using $() over backticks is that you can cascade them. In the example below we use this possibility to get a list of all files installed with rpm on the system:
 
−
filelist=$([[rpm]] -ql $(rpm -qa))
 
−
You can use the piping approach if you need to cascade in sh, but this is not focus of this bash tutorial.
 
−
 
 
−
== common mistakes ==
 
−
Usually unexperienced programmers try something like
 
−
uname -m | read arch
 
−
which [http://mywiki.wooledge.org/BashFAQ/024 does not work]. You must embed the read into a while loop.
 
−
 
 
−
= conditions =
 
−
The easiest form of a condition in bash is this '''if''' example:
 
−
<source>
 
−
echo "what is your name? "
 
−
read name
 
−
if [ $name = "Thorsten" ]; then echo "I know you"; fi
 
−
</source>
 
−
Now let's look closer at this, why does it work? Why is there a blank needed behind the [ sign? The answer is that [ is just an ordinary [[command]] in the shell. It delivers a return code for the expression that follows till the ] sign. To prove this we can write a script:
 
−
<source>
 
−
  if true; then echo "the command following if true is being executed"; fi
 
−
if false; then echo "this will not be shown"; fi
 
−
</source>
 
−
 
 
−
== empty strings ==
 
−
An empty string evaluates to false inside the [ ] operators so it is possible to check if a string ''result'' is empty like this:
 
−
# result=
 
−
# if [ $result ]; then echo success; fi
 
−
# result=good
 
−
# if [ $result ]; then echo success; fi
 
−
success
 
−
 
 
−
== arithmetic expressions ==
 
−
You can compare integer numbers like this:
 
−
<source>
 
−
echo "what is your age? "
 
−
read age
 
−
if (( $age >= 21 )); then echo "Let's talk about sex."; fi
 
−
</source>
 
−
However bash does not understand floating point numbers. To compare floating numbers you will use external programs such as bc:
 
−
<source>
 
−
$ if [ $(echo "2.1<2.2"|bc) = 1 ]; then echo "correct"; else echo "wrong"; fi
 
−
correct
 
−
$ if [ $(echo "2.1>2.2"|bc) = 1 ]; then echo "correct"; else echo "wrong"; fi
 
−
wrong
 
−
</source>
 
  
−
== not equal ==
+
= Check the Setup =
−
To check if a variable is NOT equal to whatever, use !=:
+
If cheese starts, but does not find a webcam, you need to dig deeper.
 +
* [[open a console]] and list your video4linux devices:
 
<source>
 
<source>
−
  if [ "$LANG" != "C" ]; then echo "please set your system lanugage to C"; fi
+
  ls -ltr /dev/video*
 
</source>
 
</source>
−
 
+
* you will find an output like this:
−
== common mistakes ==
 
−
Common mistakes are:
 
−
* to forget the blank behind/before the [ or ] character
 
−
* to forget the blank behind/before the equal sign
 
−
* see [[what does "unary operator expected" mean]]
 
−
 
 
−
= Redirections =
 
−
To redirect the output of a [[command]] to a file you have to consider that there are two output streams in UNIX, [[stdout,stderr and stdin|stdout and stderr]].
 
−
 
 
−
= filling files =
 
−
To create a file, probably the easiest way is to use [[cat]]. The following example writes text into README till a line occurs that only contains the string "EOF":
 
−
cat >README<<EOF
 
−
This is line 1
 
−
This is line 2
 
−
This is the last line
 
−
EOF
 
−
Afterwards, README will contain the 3 lines below the cat command and above the line with EOF.
 
−
 
 
−
= loops =
 
−
 
 
−
== for loops ==
 
−
Here is an example for a for-loop. It makes a [[backup]] of all text files:
 
−
for i in *.txt; do [[cp]] $i $i.bak; done
 
−
The above command takes each .txt file in the current directory, stores it in the [[variable]] $i and copies it to $i.bak. So ''file''.txt gets copied to ''file''.txt.bat.
 
−
 
 
−
You can also use subsequent numbers as a for loop using the command seq like this:
 
−
for i in $([[seq]] 1 1 3); do [[echo]] $i; done
 
−
 
 
−
== while loops ==
 
−
$ while true; do read line; done
 
−
 
 
−
= negations =
 
−
You can negate a result with the ! operator. $? is the last command's return code:
 
−
# true
 
−
# echo $?
 
−
0
 
−
# false
 
−
# echo $?
 
−
1
 
−
# ! true
 
−
# echo $?
 
−
1
 
−
# ! false
 
−
# echo $?
 
−
0
 
−
So you get an endless loop out of:
 
−
while ! false; do echo hallo; done
 
−
 
 
−
The following code checks the file /tmp/success to contain "success". As long as this is ''not'' the case it continues checking:
 
−
while ! (grep "success" /tmp/success)
 
−
do
 
−
  sleep 30
 
−
done
 
−
 
 
−
The following code checks if the file dblog.log exists. As long as this is not the case it tries to download it via ftp:
 
 
<source>
 
<source>
−
  while ! (test -e dblog.log); do
+
  crw-rw----+ 1 root video 81, 0 Nov 11 09:06 /dev/video0
−
  ftp -p ftp://user:password@server/tmp/dblog.log >/dev/null
 
−
  echo -en "."
 
−
  sleep 1
 
−
done
 
 
</source>
 
</source>
 +
In this example your webcam device is named ''/dev/video0''. If you have no /dev/video file, read [[#Troubleshooting]]. If you have several video4linux devices, for example a [[tv card]] your webcam may show up as /dev/video1 or whatever. But the time (in this case Nov 11 09:06) will be the time when you plugged it in.
  
−
== common mistakes ==
+
You can also test your webcam the following ways:
−
* bash is very picky regarding spaces. There MUST be a space after the ! if it means negation.
+
* if you have [[vlc]] installed you can start it and choose Media -> Open Capture Device -> Video device name = ''/dev/video0'' -> Play
−
 
+
* if you have mplayer installed you can use the command
−
= sending a process to the background =
 
−
To send a process to the [[background]], use the ampersand sign (&):
 
−
firefox & echo "Firefox has been started"
 
−
You see a newline is not needed after the &
 
−
 
 
−
= forking a process =
 
−
You can build a process chain using parantheses. This is useful if you want to have two instruction streams being executed in parallel:
 
 
<source>
 
<source>
−
  (find -iname "helloworld.txt") & (sleep 5; echo "Timeout exceeded, killing process"; kill $!)
+
  mplayer tv:// -tv driver=v4l2:width=640:height=480:device=/dev/video0 -fps 30
 
</source>
 
</source>
  
−
= functions =
+
= Troubleshooting =
−
To define a function in bash, use a non-keyword and append opening and closing parentheses. Here a function greet is defined and it prints "Hello, world!". Then it is called:
+
Troubleshooting heavily depends on the distribution and version you are using. If you have done cabling correctly and a device file /dev/video* does not appear, your kernel probably does not know the hardware. In this case you may have to install the device driver separately because it may not be part of the kernel.
−
# greet()
 
−
{
 
−
    echo "Hello, world"
 
−
}
 
−
# greet
 
−
 
 
−
If you hand over parameters you can greet any planet you like:
 
−
# greet()
 
−
{
 
−
    echo "Hello, $1"
 
−
}
 
−
# greet Mars
 
−
Hello, Mars
 
−
# greet World
 
−
Hello, World
 
−
 
 
−
= react on CTRL_C =
 
−
The command trap allows you to trap CTRL_C keystrokes so your script will not be aborted
 
−
<source>
 
−
#!/bin/bash
 
−
 
 
−
trap shelltrap INT
 
−
 
 
−
shelltrap()
 
−
{
 
−
    echo "You pressed CTRL_C, but I don't let you escape"
 
−
}
 
  
−
while true; do read line; done
+
== SUSE Linux 11.0 and earlier ==
 +
This has been tested with SUSE Linux 11.0 x64 but should work with any earlier SUSE version. You will need to log in as user root.
 +
To find out what driver you need, [[open a console]] and call
 +
[[hwinfo]] --usb
 +
If a Logitech Quickcam Messenger is plugged in the answer will be like:
 +
<source highlight=23>
 +
06: USB 00.2: 0000 Unclassified device
 +
  [Created at usb.122]               
 +
  UDI: /org/freedesktop/Hal/devices/usb_device_46d_8da_noserial_if2
 +
  Unique ID: Eopr.vE+cdFBwClB                                     
 +
  Parent ID: uIhY.uOe2OKugI8D                                     
 +
  SysFS ID: /devices/pci0000:00/0000:00:1a.2/usb3/3-1/3-1:1.2     
 +
  SysFS BusID: 3-1:1.2                                           
 +
  Hardware Class: unknown                                         
 +
  Model: "Logitech QuickCam Messanger"                           
 +
  Hotplug: USB                                                   
 +
  Vendor: usb 0x046d "Logitech, Inc."                             
 +
  Device: usb 0x08da "QuickCam Messanger"                         
 +
  Revision: "1.00"                                               
 +
  Driver: "snd-usb-audio"                                         
 +
  Driver Modules: "snd_usb_audio"                                 
 +
  Speed: 12 Mbps                                                 
 +
  Module Alias: "usb:v046Dp08DAd0100dc00dsc00dp00ic01isc02ip00"   
 +
  Driver Info #0:                                                 
 +
    Driver Status: quickcam_messenger is active                   
 +
    Driver Activation Cmd: "modprobe quickcam_messenger"
 +
  Driver Info #1:                                                 
 +
    Driver Status: gspca is active                               
 +
    Driver Activation Cmd: "modprobe gspca"
 +
  Config Status: cfg=new, avail=yes, need=no, active=unknown     
 +
  Attached to: #20 (Hub)
 
</source>
 
</source>
 +
This means you can install and load the webcam driver like this:
 +
yast -i gspcav-kmp-default
 +
modprobe gspca
 +
Now you should see a video device:
 +
ls /dev/video*
 +
/dev/video  /dev/video0
 +
That means you can install and start your webcam-viewer-software. We choose gqcam:
 +
yast -i gqcam
 +
gqcam
 +
It works. You see a video what from what is going on in front of your webcam.
  
−
;Note: You can still ''pause'' your script by pressing CTRL_Z, send it to the [[background]] and kill it there. To catch CTRL_Z, replace INT by TSTP in the above example. To get an overview of all signals that you might be able to trap, [[open a console]] and enter
+
== Ubuntu ==
−
  kill -l
+
This has been tested with Ubuntu 8.10 x32 but should work with any Ubuntu version.
−
 
+
Find out the driver activation command of your webcam. For this, first install the software '''hwinfo'''. [[Open a console]] and type:
−
= helpful programs =
+
  sudo apt-get [[install]] [[hwinfo]]
−
== awk: read a specific column ==
+
Then call hwinfo:
−
[[awk]] is a program that is installed on almost all Linux distributions. It is a good helper for text stream processing. It can extract columns from a text. Let's imagine you want to use the [[program]] [[vmstat]] to find out how high the CPU user load was. Here is the output from vmstat:
+
hwinfo --usb
−
 
+
If a Logitech Quickcam Messenger is plugged in the response will be like:
−
<pic src="http://www.linuxintro.org/images/vmstat.png" align=text width=100% caption=VmStat  />
+
<source highlight=20>
−
 
+
04: USB 00.2: 0000 Unclassified device
−
We see the user load is in colum 13, and we only want to print this column. We do it with the following command:
+
  [Created at usb.122]
−
vmstat 5 | awk '{print $13}'
+
  UDI: /org/freedesktop/Hal/devices/usb_device_46d_8da_noserial_if2
−
This will print a line from vmstat all 5 seconds and only write the column 13. It looks like this:
+
  Unique ID: 4ajv.vE+cdFBwClB
−
# vmstat 5 | awk '{print $13}'
+
  Parent ID: k4bc._Mkd+LmXb03
−
+
  SysFS ID: /devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb1/1-1/1-1:1.2
−
us
+
  SysFS BusID: 1-1:1.2
−
1
+
  Hardware Class: unknown
−
1
+
  Model: "Logitech QuickCam Messanger"
−
0
+
  Hotplug: USB
−
1
+
  Vendor: usb 0x046d "Logitech, Inc."
−
To store the CPU user load into a variable we use
+
  Device: usb 0x08da "QuickCam Messanger"
−
<source>
+
  Revision: "1.00"
−
load=$(vmstat 1 2 | tail -n 1 | awk '{print $13}')
+
  Driver: "snd-usb-audio"
−
</source>
+
  Driver Modules: "snd_usb_audio"
−
What happens here? First vmstat outputs some data in its first line. The data about CPU load can only be rubbish because it did not have any time to measure it. So we let it output 2 lines and wait 1 second between them ( => vmstat 1 2 ). From this command we only read the last line ( => tail -n 1 ). From this line we only print column 13 ( => awk '{print $13}' ). This output is stored into the variable $load ( => load=$(...) ).
+
  Speed: 12 Mbps
 +
  Module Alias: "usb:v046Dp08DAd0100dc00dsc00dp00ic01isc02ip00"
 +
  Driver Info #0:
 +
    Driver Status: gspca_zc3xx is active
 +
    Driver Activation Cmd: "modprobe gspca_zc3xx"
 +
  Config Status: cfg=new, avail=yes, need=no, active=unknown
 +
  Attached to: #8 (Hub)</source>
 +
Activate the driver:
 +
sudo modprobe gspca_zc3xx
 +
Now you should be able to see the video device:
 +
[[ls]] /dev/video*
 +
/dev/video0
 +
You can now test your webcam using the software cheese:
 +
sudo apt-get install cheese
 +
cheese
  
−
== grep: search a string ==
+
== Other webcams ==
−
[[grep]] is a [[program]] that is installed on almost all Linux distributions. It is a good helper for text stream processing. It can extract lines that contain a string or match a [[regex]] pattern. Let's imagine you want all external links from www.linuxintro.org's main page:
+
If you have another webcam, try the above nevertheless. If it does not work, exchange the driver gspca against uvcvideo:
−
<source>
+
  yast -i uvcvideo_kmp_default
−
  wget -O linuxintro.txt http://www.linuxintro.org
+
  modprobe uvcvideo
−
  grep "http:" linuxintro.txt
+
and start gqcam again.
−
</source>
 
  
−
== sed: replace a string ==
+
= Use it =
−
[[sed]] is a [[program]] that is installed on almost all Linux distributions. It is a good helper for text stream processing. It can replace a string by another one. Let's imagine you want to print your distribution's name, but lsd_release outputs too much:
 
−
# lsb_release -d
 
−
Description:    openSUSE 12.1 (x86_64)
 
−
You want to remove this string "Description" so you replace it by nothing:
 
−
lsb_release -d | sed "s/Description:\t//"
 
−
openSUSE 12.1 (x86_64)
 
  
−
Once you understand [[regular expressions]] you can use sed with them:
+
== record video ==
 +
to capture video streams you can use [http://en.wikipedia.org/wiki/Cheese_%28software%29 cheese], a nice program with a graphical user interface. It allows you to watch and record your camera output at the same time. It stores in a strange format (.webm), but [[vlc]] can play this.
  
−
* to replace protocol names for a given port (in this case 3200) in /etc/services:
+
You can also automate video recording so you can capture the camera stream with sitting in front of the computer. To do this you can
 +
* use the software ''mencoder'':
 
<source>
 
<source>
−
  sed -ri "s/.{16}3200/sapdp00 3200/" /etc/services
+
  mencoder tv:// -tv driver=v4l2:width=320:height=240:device=/dev/video0 -nosound -ovc lavc -o myvideo.avi
 
</source>
 
</source>
−
* if you have an [[apache]] [[web server]] here's how you get the latest websites that have been requested:
+
* or use the software ''streamer'', example:
 
<source>
 
<source>
−
  cat /var/log/apache2/access_log | sed ";.*\(GET [^\"]*\).*;\1;"
+
  streamer -c /dev/video0 -f jpeg -F stereo -o myvideo.avi -t 0:05
 
</source>
 
</source>
  
−
== tr: replace linebreaks ==
+
== video conferencing ==
−
[[sed]] is a [[program]] that is installed on almost all Linux distributions. It is a good helper for text stream processing. It can replace a character by another one, even over line breaks.
+
* to do video conferencing, [[use skype under Linux]].
−
For example here is how you remove all empty lines from your processor information:
 
−
<source>
 
−
# cat /proc/cpuinfo | while read a; do ar=$(echo -n $a|tr '\n' ';')
 
−
if [ "$ar" <> ";" ]; then echo "$ar"; fi; done
 
−
</source>
 
  
−
== wc: count ==
+
== watch it ==
−
With the command wc you can count words, characters and lines. wc -l counts lines. For example to find out how many semicolons are in a line, use the following statement:
+
To watch your camera's input, use ''cheese'' or mplayer:
 
<source>
 
<source>
−
  while read line
+
  mplayer -fps 30 -cache 128 -tv driver=v4l2:width=640:height=480:device=/dev/video0 tv://
−
do echo "$line" | tr '\n' ' ' | sed "s/;/\n/g" | wc -l
 
−
done
 
 
</source>
 
</source>
−
It lets you input a line of text, counts the semicolons in it and outputs the number.
+
Or use [[vlc]]. You can [[run vlc as root]] by the way. To watch your webcam /dev/video0, start vlc and select Media -> Open Capture Device -> Video device name = /dev/video0 -> Play
−
 
 
−
How does it do this?
 
  
−
It reads lines from your keyboard (while read line). It outputs the line (echo "$line"), but it does not output it in the console. The pipe (|) redirects the output to the input stream of the command tr. The command tr replaces the ENTER ('\
+
= Testbed =
−
') by a space (' '). The pipe (|) redirects the output to the input stream of sed. sed substitutes ("s/) the semicolon (;) by (/) a linefeed (\
+
The following webcams have been found working with this tutorial:
−
), globally (/g"). The pipe redirects the output to the input stream of the wc -l command that outputs the count of lines.
+
* Logitech Quickcam messenger
 +
* Philips Webcam SPC220NC
  
−
== dialog: create dialogs ==
+
A general list of working webcams can be found at http://mxhaard.free.fr/spca5xx.html.
−
Dialog is a command that helps you creating dialogs in the shell. The answers given by the user are send to [[stderr]] and/or influence the command's return code. For example if you run this script:
 
−
<source>
 
−
#!/bin/bash
 
−
if (dialog --title "Message"  --yesno "Are you having fun?" 6 25)
 
−
then echo "glad you have fun"
 
−
else echo "sad you don't have fun"
 
−
fi
 
−
</source>
 
−
It will display this dialog:
 
  
−
<pic src=http://www.linuxintro.org/images/Snapshot-dialog.png />
+
The guide has been tested with SUSE Linux 11.4 till 13.2 and Ubuntu.
−
 
 
−
This has been taken from http://www.linuxjournal.com/article/2807. Read there for more info.
 
  
 
= See also =
 
= See also =
−
* [[bash]]
+
* [[hardware]]
−
* [[shell]]
+
* http://en.opensuse.org/Webcam
−
* [[scripting]]
+
* http://www.linux.com/feature/126186
−
* [[bash operators]]
+
* http://ubuntulinuxhelp.com/linux-driver-for-quickcam-usb-cameras-logitech-quickcam-fusion/
−
* http://en.wikibooks.org/wiki/Bash_Shell_Scripting
+
* http://www.goldmann.de/webcam-linux_tipp_408.html
−
* http://ryanstutorials.net/linuxtutorial/scripting.php
+
* http://wiki.ubuntuusers.de/Webcam
−
* http://wiki.linuxquestions.org/wiki/Bash_tips
 
−
* http://wiki.linuxquestions.org/wiki/Bash
 
−
* http://linuxconfig.org/Bash_scripting_Tutorial
 
−
* http://steve-parker.org/sh/intro.shtml
 
−
* http://mywiki.wooledge.org/BashFAQ
 
−
* http://mywiki.wooledge.org/BashPitfalls
 
−
 
 
−
[http://www.facebook.com/sharer.php?u=http%3A%2F%2Fwww.linuxintro.org%2Fwiki%2FShell_scripting_tutorial&t=Shell%20scripting%20Tutorial&src=sp Share on Facebook]
 
  
 
<stumbleuponbutton />
 
<stumbleuponbutton />
−
 
−
[[Category:Mindmap]]
 
−
[[Category:Learning]]
 

Revision as of 12:28, 26 December 2020

Screenshot from 2020-03-01 13-18-32.png You want to set up your webcam with Linux, see a video stream from it and learn which applications you can use with it, right? Then this article is for you.

Try it

First let's try if it works out of the box, so, connect your webcam (if it's not inbuilt), open a terminal and start the application cheese: 

cheese

This should switch on your webcam and you should see what it's recording.

Ok, you are reading on, so there is still something left, maybe:

Install cheese

To install cheese, you need to know your distribution. Here is how to find out your distribution.

  • for Debian, Raspbian, Ubuntu, Kubuntu, Flubuntu, Xubuntu, GEUbuntu, Edubuntu, ...:
sudo apt-get install cheese
  • for SUSE:
yast -i cheese

Check the Setup

If cheese starts, but does not find a webcam, you need to dig deeper.

<source> 

ls -ltr /dev/video*

</source>

  • you will find an output like this:

<source> 

crw-rw----+ 1 root video 81, 0 Nov 11 09:06 /dev/video0

</source> In this example your webcam device is named /dev/video0. If you have no /dev/video file, read #Troubleshooting. If you have several video4linux devices, for example a tv card your webcam may show up as /dev/video1 or whatever. But the time (in this case Nov 11 09:06) will be the time when you plugged it in.

You can also test your webcam the following ways:

  • if you have vlc installed you can start it and choose Media -> Open Capture Device -> Video device name = /dev/video0 -> Play
  • if you have mplayer installed you can use the command

<source> 

mplayer tv:// -tv driver=v4l2:width=640:height=480:device=/dev/video0 -fps 30

</source>

Troubleshooting

Troubleshooting heavily depends on the distribution and version you are using. If you have done cabling correctly and a device file /dev/video* does not appear, your kernel probably does not know the hardware. In this case you may have to install the device driver separately because it may not be part of the kernel.

SUSE Linux 11.0 and earlier

This has been tested with SUSE Linux 11.0 x64 but should work with any earlier SUSE version. You will need to log in as user root. To find out what driver you need, open a console and call 

hwinfo --usb

If a Logitech Quickcam Messenger is plugged in the answer will be like: <source highlight=23> 06: USB 00.2: 0000 Unclassified device 

 [Created at usb.122]                
 UDI: /org/freedesktop/Hal/devices/usb_device_46d_8da_noserial_if2
 Unique ID: Eopr.vE+cdFBwClB                                      
 Parent ID: uIhY.uOe2OKugI8D                                      
 SysFS ID: /devices/pci0000:00/0000:00:1a.2/usb3/3-1/3-1:1.2      
 SysFS BusID: 3-1:1.2                                             
 Hardware Class: unknown                                          
 Model: "Logitech QuickCam Messanger"                             
 Hotplug: USB                                                     
 Vendor: usb 0x046d "Logitech, Inc."                              
 Device: usb 0x08da "QuickCam Messanger"                          
 Revision: "1.00"                                                 
 Driver: "snd-usb-audio"                                          
 Driver Modules: "snd_usb_audio"                                  
 Speed: 12 Mbps                                                   
 Module Alias: "usb:v046Dp08DAd0100dc00dsc00dp00ic01isc02ip00"    
 Driver Info #0:                                                  
   Driver Status: quickcam_messenger is active                    
   Driver Activation Cmd: "modprobe quickcam_messenger"
 Driver Info #1:                                                  
   Driver Status: gspca is active                                 
   Driver Activation Cmd: "modprobe gspca"
 Config Status: cfg=new, avail=yes, need=no, active=unknown       
 Attached to: #20 (Hub)

</source> This means you can install and load the webcam driver like this: 

yast -i gspcav-kmp-default
modprobe gspca

Now you should see a video device: 

ls /dev/video*
/dev/video  /dev/video0

That means you can install and start your webcam-viewer-software. We choose gqcam: 

yast -i gqcam
gqcam

It works. You see a video what from what is going on in front of your webcam.

Ubuntu

This has been tested with Ubuntu 8.10 x32 but should work with any Ubuntu version. Find out the driver activation command of your webcam. For this, first install the software hwinfo. Open a console and type: 

sudo apt-get install hwinfo

Then call hwinfo: 

hwinfo --usb

If a Logitech Quickcam Messenger is plugged in the response will be like: <source highlight=20> 04: USB 00.2: 0000 Unclassified device 

 [Created at usb.122]
 UDI: /org/freedesktop/Hal/devices/usb_device_46d_8da_noserial_if2
 Unique ID: 4ajv.vE+cdFBwClB
 Parent ID: k4bc._Mkd+LmXb03
 SysFS ID: /devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb1/1-1/1-1:1.2
 SysFS BusID: 1-1:1.2
 Hardware Class: unknown
 Model: "Logitech QuickCam Messanger"
 Hotplug: USB
 Vendor: usb 0x046d "Logitech, Inc."
 Device: usb 0x08da "QuickCam Messanger"
 Revision: "1.00"
 Driver: "snd-usb-audio"
 Driver Modules: "snd_usb_audio"
 Speed: 12 Mbps
 Module Alias: "usb:v046Dp08DAd0100dc00dsc00dp00ic01isc02ip00"
 Driver Info #0:
   Driver Status: gspca_zc3xx is active
   Driver Activation Cmd: "modprobe gspca_zc3xx"
 Config Status: cfg=new, avail=yes, need=no, active=unknown
 Attached to: #8 (Hub)</source>

Activate the driver: 

sudo modprobe gspca_zc3xx

Now you should be able to see the video device: 

ls /dev/video*
/dev/video0

You can now test your webcam using the software cheese: 

sudo apt-get install cheese
cheese

Other webcams

If you have another webcam, try the above nevertheless. If it does not work, exchange the driver gspca against uvcvideo: 

yast -i uvcvideo_kmp_default
modprobe uvcvideo

and start gqcam again.

Use it

record video

to capture video streams you can use cheese, a nice program with a graphical user interface. It allows you to watch and record your camera output at the same time. It stores in a strange format (.webm), but vlc can play this.

You can also automate video recording so you can capture the camera stream with sitting in front of the computer. To do this you can

  • use the software mencoder:

<source> 

mencoder tv:// -tv driver=v4l2:width=320:height=240:device=/dev/video0 -nosound -ovc lavc -o myvideo.avi

</source>

  • or use the software streamer, example:

<source> 

streamer -c /dev/video0 -f jpeg -F stereo -o myvideo.avi -t 0:05

</source>

video conferencing

watch it

To watch your camera's input, use cheese or mplayer: <source> 

mplayer -fps 30 -cache 128 -tv driver=v4l2:width=640:height=480:device=/dev/video0 tv://

</source> Or use vlc. You can run vlc as root by the way. To watch your webcam /dev/video0, start vlc and select Media -> Open Capture Device -> Video device name = /dev/video0 -> Play

Testbed

The following webcams have been found working with this tutorial:

  • Logitech Quickcam messenger
  • Philips Webcam SPC220NC

A general list of working webcams can be found at http://mxhaard.free.fr/spca5xx.html.

The guide has been tested with SUSE Linux 11.4 till 13.2 and Ubuntu.

See also

Retrieved from "http://linuxintro.org/index.php?title=BaBE_-_Bash_By_Examples&oldid=19526"