Cut string from command output

Question

I would like to cut 150.8 from this string temp1: +150.8°F (crit = +197.6°F). Here is my script for logging temperatures with the command sensors:

#!/bin/bash
now=$(date +"%m_%d_%Y")    # get current date
now_excel=$(date +"%D %H:%M")    # get current date & time in excel format

file_dir="/var/www/html/logs"
file="$file_dir/logging_$now.csv"    # backup name and directory

temp=$(sensors -Af | sed -n '2{p;q}')    # temp1:       +150.8°F  (crit = +197.6°F)
#temp_num="$temp" | sed 's/+\(.*\)°/\1/g'

# add line to csv
printf "$now_excel" >> "$file"
printf ", " >> "$file"
printf "$temp" >> "$file"
printf "\n" >> "$file"

find "$file_dir"/* -mtime +3 -exec rm {} \;    # remove any backup files older than 3 days

exit 0

Answer 1

Using sed

Here is one way:

$ sensors -Af | sed -n '2{s/°.*//; s/[^+-]*//; p; q}'
+105.8

Or, using the same command inside command substitution to capture its output in a variable:

temp=$(sensors -Af | sed -n '2{s/°.*//; s/[^+-]*//; p; q}')

s/°.*// removes the first occurrence of the degree symbol, °, and everything after it. s/[^+-]*// removes everything up to but not including the first + or -.

Using awk

$ sensors -Af | awk 'NR==2{print $3+0; exit;}'
105.8

The number that we want is in the third field. Because the third field contains characters, for example +105.8°F, we add 0 to it. This forces awk to convert it to what we want: a number.