Tag: bash

Using the REST api to read sensors on Home assistant

9 November 202114 March 2023 Fabien Linux, Networking Leave a comment

During one of my little project of making timelapses videos with some IP cameras, I had the following problem : How do you stop capturing new images at night when the camera see nothing,
After all , the sun rise and sun set time are changing everyday ! and i didn’t see a simple way to calculate this.
then i remembered the sun.sun integration in Home assistant.

If i had a simple way to query this integration in my script , i could very simply stop my script when the sun was no longer present in the sky !

The Home assistant REST API

In any home assistant installation there is access to a REST API that lets you do a lot a things , but in my case, I don’t want much , I just want to know if the sun is above or below the horizon.

Get a Authorization: Bearer token
you first have to generate a token to authenticate your request . You have to go to your user section , this is the circle a the bottom of the toolbar, then at the bottom of the page , you can create a long term token ,
Please take note of this token because Home assitant can only display it one time , if you loose it , you must recreate an other one.

Then in my script i can use this

curl -s -X GET -H "Authorization: Bearer eyJ0eX....G9QCqY" -H "Content-Type: application/json" http://192.168.1.13:8123/api/states/sun.sun |jq -r .state

it will return either above_horizon or below_horizon, I can then use this in my script to stop the capture when it’s below_horizon

I used jq filter the json result , but , if you can’t or don’t want to install it , you can replace it with this simple awk

 awk -F "\"" {'print $8'}

Using bash and gatttool to get readings from Xiaomi Mijia LYWSD03MMC Temperature Humidity sensor

23 January 20205 November 2020 Fabien bash, Linux 21 Comments

There is a new inexpensive Temperature and humidity sensor by xiaomi.
This time is no longer round ,

Xiaomi Mijia LYWSD03MMC Bluetooth 4.2 Temperature Humidity sensor

if you like me would like to get the temperature and humidity data from time to time to import in a graphing tool like grafana, there is a simple solution using classic bash tools and gatttool.
First you have to indentify the mac-address of your little sensor, for this , just make sure the sensor is in range of your linux device ans launch a
hcitool lescann

this command will spit out all the bluetooth devices in range
just find the line with the name of the device and copy the mac address A4:C1:38:8C:77:CA LYWSD03MMC

then you must start a little bash script like this :

#!/bin/bash bt=$(timeout 15 gatttool -b A4:C1:38:8C:77:CA --char-write-req --handle='0x0038' --value="0100" --listen) if [ -z "$bt" ] then echo "The reading failed" else echo "Got data" echo $bt temphexa=$(echo $bt | awk -F ' ' '{print $12$11}'| tr [:lower:] [:upper:] )
humhexa=$(echo $bt | awk -F ' ' '{print $13}'| tr [:lower:] [:upper:])
temperature100=$(echo "ibase=16; $temphexa" | bc)
humidity=$(echo "ibase=16; $humhexa" | bc)
echo "scale=2;$temperature100/100"|bc
echo $humidity fi

this is a skeleton that you can improve , but for now it pretty much work like that ,

first it use gatttol to connect to the sensor and listen for 15 sec
During these fifteen seconds , you can be pretty much sure to receive at least some data like this :

Characteristic value was written successfully Notification handle = 0x0036 value: 58 03 47 a0 0b Notification handle = 0x0036 value: 55 03 47 a0 0b

this tell me that during the 15 sec of connection i received the information that i need two times.
what i’m after are the value 58 03 for the temperature , and 47 for the humidity.

the temperature is little endian format its mean that the two group must be inverted before decoding the data. i invert the values with awk and decode them using bc.
bc doesn’t like when the hex values are not capitalised so tr is used to do that.

bc then give you the temperature multiplied by 100. relaunch bc to divice per 100,

For the humidity its simpler , you get the value in one step without inverting anyting

Then you can do what you need with theses two vars , insert then in some database etc ..

there is room from improvement: for example this script is not capable of decoding negative temperature.
i will post an improved version when i figure out how to do it

Test the existence of a file in bash

11 July 201923 January 2020 Fabien bash Leave a comment

If you need to test in a bash script if a file exist you can launch the following command.

if [ -f /tmp/dnsmasq_leases.log ];then
         echo "The file exist"
 else
        echo "The file doesn't exist"
 fi

Note if the file exist , but , is empty this also test true and tell you that the file exist

space char directly after var in bash

11 July 201923 January 2020 Fabien bash, Linux Leave a comment

In bash space is used to determine the end of a variable ,

for example when you launch

var = abcd
echo $var ef

this will display abcd ef ,if you try to to display abcdef you can‘t do echo $varef

the solution to this little problem is : is to use curly brackets.

var = abcd
echo ${var}ef

will display abcdef

Bash – Loop over the content of a file line by line

20 June 201810 October 2018 Fabien bash, Linux Leave a comment

If you need to iterate over the content of a file line by line
You can use this little bash trick.

while read -r line; do
printf '%s\n' "$line"
done < "file.txt"

In this case , it will simply print the line, but if you need to do an operation on the text , just insert your code into the while loop.

Bash keyboard shortcuts

15 February 201815 February 2018 Fabien bash, Linux Leave a comment

When you are spending your day in the terminal , you will find that navigating using only the arrows keys although fine at the the start will frustrate you because it’s quite slow.
Bash come with a lot of keyboard shortcuts design to gain precious time.
CTRL+A # will move the cursour to the beginning of the line CTRL+E # moves to end of line CTRL+C # halts the current command and back to prompt CTRL+D # deletes one character backward or logs out of current session, similar to exit CTRL+K # deletes all the text forward to the end of the line CTRL+L # clears screen and redisplay the line CTRL+R # searches history entering keyword , CTRL+T # transposes two characters CTRL+U # kills backward from point to the beginning of line CTRL+W # kills the word behind the cursor

i’ve put in bold the shortcuts that i use every day , i don’t use CTRL+A and CTRL+E because the keyboard has keys that are foing the same thing.

Bash brace expansion. (to delete files)

3 February 2018 Fabien bash, Linux Leave a comment

In bash , it is common to have to do some action on a numéric serie of files , like deleting or renaming ,

Using brace expansion you will be able to générate a single line that will act on multiple targets ,

For our example , let’s think about a list of ten files

log1.log log2.log log3.log log4.log log5.log
log6.log log7.log log8.log log9.log log10.log

in the simple case where i want to delete the complete list of files, i just have to run de command,

rm log*.log

The 10 files will be deleted, but , this is not practical if you want to keep the last file , and delete the other nine,

In that case we can use a usefull tool called brace expansion,

To delete the files 1 to 9 , i just have to run in my bash terminal!

rm log{1..9}.log

This last one is extremely practical , I use it very often in a lot of different uses cases.

But in other cases , you may want to delete even on odd files , or one every three files,

This is also doable with braces expansions

rm log{1..10..2} .log
#to delete  1 3 5 7 9
rm log{1..10..3}.log
#to delete 1 4 7 10

Redirect stdout and stderr to a file

22 November 201722 November 2017 Fabien bash Leave a comment

il you need to run a script unattended and wish to log the output of that script you must already know that you can simply do

 ./myscript.sh > mylog.log

the problem with that is you will not log the error messages , only the output messages ,
the error are going to be displayed on the terminal but , not logged
and the error message are often as important as the output message , we do not want to dismiss them from the log ,

the solution to that issue is to run the script using this

 ./myscript.sh > mylog.log 2>&1

With this , both the output will be logged in to the log file.

Bash script to clean movies name

22 June 201722 June 2017 Fabien bash, Linux 3 Comments

The issue when you download movies online, is that most of the time the file name is going to be complete trash , filled with useless info like the team that made the rip or the website from where the movie was downloaded.
This is very annoying when you sort by name and the website made the idiotic decision to put their name in front of the actual film name.

for example here a typical movie name
[ Torrent9.info ] Dont.Think.Twice.2016.FRENCH.WEBRip.XviD-NEWCiNE.avi
the actual useful data that i wish to keep is Dont.Think.Twice.2016.avi

for this purpose i’ve developped a small bash script that will list all the files in a chosen directory then , if necessary , will rename the file.

#!/bin/bash
#the location of the folder full of movies to rename.
for file in /media/freebox/*
do
if [[ -f $file ]]; then
#that line will delete all the text after the date but keep the file extension.
nfile=$(echo $file | sed "s/\(20[0-1][0-8]\).*\(mkv\|avi\|mp4\)/\1.\2/")

#this line is going to try to delete a space a the start of the filename if it exist
nfile=$(echo $nfile | sed  "s/\/ /\//")

#this line is going to delete double dots in the filename and replace them with simple dots
nfile=$(echo $nfile | sed -e "s/\.\./\./g")

#that line is going to delete everything between [] including the [] 
nfile=$(echo $nfile | sed -e 's/\[[^][]*\]//g')


#after all this work on the filename
#you can now check if the any changes have been made , 

if [[ "$file" == "$nfile" ]]
then
   #if no change display this
   echo "Not touched : $file"
else
   #if change detected , rename the file
   echo ______
   echo Renamed :
   echo "Original name : $file"
   echo "Renamed to  : $nfile"
   echo ______
#doing the actual renaming
mv "$file" "$nfile"
fi
fi
done

this is not a very efficient script
but it’s fulfill it’s purpose and very rarely encounter a filename that he is unable to clean.

BASH:check if a number is even or odd

19 June 201719 June 2017 Fabien Linux 5 Comments

In a bash script you might need to check if a var is even or odd ,

in my case im going to use a if to make that check

#!/bin/bash
for i in $(seq 10);do
    if (( $i % 2 )); then
        echo $i is odd
    else
        echo $i is even
    fi
done

You can use this simple code to make that check and display the result.

the result will be :


1 is odd
2 is even
3 is odd
4 is even
5 is odd
6 is even
7 is odd
8 is even
9 is odd
10 is even