How to filter only digits from a string in bash shell scripting?

Question

I want to measure temperature of Raspberry pi 3, and change the background color of the text accordingly. As the code goes, we can print the temperature on the display. Now, I want to filter the digits only out of the text. And use that in the if condition. The source code goes like this:

#!/bin/bash

measurement()
{
    i=1
    echo "Reading Temperature"
    echo "Updating time is set to $1"
    while [ $i -eq 1 ]; do
        temp="$(vcgencmd measure_temp | cut -d= -f 2 | cut -d\' -f 1)"
            tput setaf 7

        if [[ $temp -ge 70 ]]; then
                    tput setab 1
                    echo -ne "Temperature = $temp\r"
        elif [[ $temp -ge 65 && $temp -le 69 ]]; then
                    put setab 3
                    echo -ne "Temperature = $temp\r"
        elif [[ $temp -ge 60  && $temp -le 64 ]]; then
                    tput setab 2
                    echo -ne "Temperature = $temp\r"
        elif [[ $temp -ge 55 && $temp -le 59 ]]; then
                        tput setab 6
                        echo -ne "Temperature = $temp\r"
        else
            tput setab 4
            echo -ne "Temperature = $temp\r"
        fi
        sleep $1
        done
}

if [ -n "$1" ]; then
        sleep_time=$1
        measurement $sleep_time
else
        read -p "Enter the Update Time: " sleep_time
        measurement  $sleep_time
fi

enter image description here

Nothing shell-specific (so it should work in not just BASH) is to use sed, the stream editor, to extract parts from a stream using regular expressions. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented Jan 13, 2018 at 13:54
Where is the problem in your bash code? What is the text which you want to filter the digits out? What is the actual output and what is the desired output? — Jdamian
– Jdamian, Commented Jan 13, 2018 at 13:57
In your case: temp="$(vcgencmd measure_temp | tr -cd '[[:digit:]]')" — William Pursell
– William Pursell, Commented Jan 13, 2018 at 14:03
@WilliamPursell Would you like to change your comment into an answer and add some explanation? That would get this out of the list of unanswered questions. — Yunnosch
– Yunnosch, Commented Jan 13, 2018 at 14:05

William Pursell · Accepted Answer · 2018-01-13 14:08:14Z

4

The typical tools for removing unwanted characters from text are tr and sed (and manipulating variables directly in the shell, with constructs like ${var##text}, but unless you want to use shell specific extensions those provide limited capability). For your use case, it seems easiest to do:

temp="$(vcgencmd measure_temp | tr -cd '[[:digit:]]')"

This simply deletes (-d) all characters that are not (-c) a member of the character class digit.

answered Jan 13, 2018 at 14:08

William Pursell

214k49 gold badges279 silver badges317 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user9156891 Over a year ago

Wow that works... However, In place of 65.9, I'm getting 659! That shows the red color!! That's 10 times higher! What should I do?

William Pursell Over a year ago

If you want to keep decimal points, include them in the list of characters that you don't want deleted. tr -cd '[[:digit:]].'

Cole Tierney · Accepted Answer · 2018-01-13 17:52:50Z

3

You could use a builtin string operation to print just the digits and periods in a variable. The following is a global substring replacement of any character that is not a digit or period with an empty string:

echo "${temp//[^0-9.]/}"

edited Jan 13, 2018 at 17:52

answered Jan 13, 2018 at 14:34

Cole Tierney

10.4k2 gold badges31 silver badges38 bronze badges

Collectives™ on Stack Overflow

How to filter only digits from a string in bash shell scripting?

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related