Extracting a substring from a variable using bash script - bash

Question

I have a bash variable with value something like this:
10:3.0,16:4.0,32:4.0,39:2.0,65:3.0,95:4.0,110:4.0,111:4.0,2312:1.0
There are no spaces within value. This value can be very long or very short. Here pairs such as 65:3.0 exist. I know the value of a number from the first part of pair, say 65. I want to extract the number 3.0 or pair 65:3.0. I am not aware of the position (offset) of 65.
I will be grateful for a bash-script that can do such extraction. Thanks.

Answer 1

Probably awk is the most straight-forward approach:
awk -F: -v RS=',' '$1==65{print $2}' <<< "$var"
3.0
Or to get the pair:
$ awk -F: -v RS=',' '$1==65' <<< "$var"
65:3.0

Answer 2

Here's a pure Bash solution:
var=10:3.0,16:4.0,32:4.0,39:2.0,65:3.0,95:4.0,110:4.0,111:4.0,2312:1.0
while read -r -d, i; do
[[ $i = 65:* ]] || continue
echo "$i"
done <<< "$var,"
You may use break after echo "$i" if there's only one 65:... in var, or if you only want the first one.
To get the value 3.0: echo "${i#*:}".
Other (pure Bash) approach, without parsing the string explicitly. I'm assuming you're only looking for the first 65 in the string, and that it is present in the string:
var=10:3.0,16:4.0,32:4.0,39:2.0,65:3.0,95:4.0,110:4.0,111:4.0,2312:1.0
value=${var#*,65:}
value=${value%%,*}
echo "$value"
This will be very slow for long strings!
Same as above, but will output all the values corresponding to 65 (or none if there are none):
var=10:3.0,16:4.0,32:4.0,39:2.0,65:3.0,95:4.0,110:4.0,111:4.0,2312:1.0
tmpvar=,$var
while [[ $tmpvar = *,65:* ]]; do
tmpvar=${tmpvar#*,65:}
echo "${tmpvar%%,*}"
done
Same thing, this will be slow for long strings!
The fastest I can obtain in pure Bash is my original answer (and it's fine with 10000 fields):
var=10:3.0,16:4.0,32:4.0,39:2.0,65:3.0,95:4.0,110:4.0,111:4.0,2312:1.0
IFS=, read -ra ary <<< "$var"
for i in "${ary[#]}"; do
[[ $i = 65:* ]] || continue
echo "$i"
done
In fact, no, the fastest I can obtain in pure Bash is with this regex:
var=10:3.0,16:4.0,32:4.0,39:2.0,65:3.0,95:4.0,110:4.0,111:4.0,2312:1.0
[[ ,$var, =~ ,65:([^,]+), ]] && echo "${BASH_REMATCH[1]}"
Test of this vs awk,
where the 65:3.0 is at the end:
printf -v var '%s:3.0,' {100..11000}
var+=65:42.0
time awk -F: -v RS=',' '$1==65{print $2}' <<< "$var"
shows 0m0.020s (rough average) whereas:
time { [[ ,$var, =~ ,65:([^,]+), ]] && echo "${BASH_REMATCH[1]}"; }
shows 0m0.008s (rough average too).
where the 65:3.0 is not at the end:
printf -v var '%s:3.0,' {1..10000}
time awk -F: -v RS=',' '$1==65{print $2}' <<< "$var"
shows 0m0.020s (rough average) and with early exit:
time awk -F: -v RS=',' '$1==65{print $2;exit}' <<< "$var"
shows 0m0.010s (rough average) whereas:
time { [[ ,$var, =~ ,65:([^,]+), ]] && echo "${BASH_REMATCH[1]}"; }
shows 0m0.002s (rough average).

Answer 3

With grep:
grep -o '\b65\b[^,]*' <<<"$var"
65:3.0
Or
grep -oP '\b65\b:\K[^,]*' <<<"$var"
3.0
\K option ignores everything before matched pattern and ignore pattern itself. It's Perl-compatibility(-P) for grep command .

Answer 4

Here is an gnu awk
awk -vRS="(^|,)65:" -F, 'NR>1{print $1}' <<< "$var"
3.0

Answer 5

try
echo $var | tr , '\n' | awk '/65/'
where
tr , '\n' turn comma to new line
awk '/65/' pick the line with 65
or
echo $var | tr , '\n' | awk -F: '$1 == 65 {print $2}'
where
-F: use : as separator
$1 == 65 pick line with 65 as first field
{ print $2} print second field

Answer 6

Using sed
sed -e 's/^.*,\(65:[0-9.]*\),.*$/\1/' <<<",$var,"
output:
65:3.0
There are two different ways to protect against 65:3.0 being the first-in-line or last-in-line. Above, commas are added to surround the variable providing for an occurrence regardless. Below, the Gnu extension \? is used to specify zero-or-one occurrence.
sed -e 's/^.*,\?\(65:[0-9.]*\),\?.*$/\1/' <<<$var
Both handle 65:3.0 regardless of where it appears in the string.

Answer 7

Try egrep like below:
echo $myvar | egrep -o '\b65:[0-9]+.[0-9]+' |