Bash - Counting substrings in a string

Feel free to try this to get the number:

echo "$CommandResult" | tr " " "\n" | grep -c "$InstanceID"

I'd use grep -o to extract the desired string from the output:

#!/bin/bashCommandResult="Interface    Chipset     Driver     mon0    Unknown      iwlwifi - [phy0]wlan0       Unknown     iwlwifi - [phy0]Interface    Chipset     Driver     mon12    Unknown      iwlwifi - [phy0]wlan0       Unknown     iwlwifi - [phy0]"for InstanceId in $(grep -o 'mon[0-9]\+' <<< "$CommandResult") ; do    echo "found $InstanceId "$(grep -c "$InstanceId" <<< "$CommandResult")' times'done

Wanted to share another solution. 3,5 years later, but better late than never I guess. ;)

I was working on a script that had to do the same, that is get the number of substrings in a string, and I was using count=$(echo '$string' | grep -o ... | wc -l) at first.
I got what I wanted, but when looping through ~1500 files with 0...8000 lines in each the performance was just terrible: the script took about 49 minutes to complete.
So, I went and searched for alternative approaches and eventually found this:

InstanceId="mon0";tmp="${CommandResult//$InstanceId}"count=$(((${#CommandResult} - ${#tmp}) / ${#InstanceId}))

Got the same result but waaaay quicker, in 8-9 minutes.

Explained:

tmp="${CommandResult//$InstanceId}"

This removes all occurrences of $InstanceId from $CommandResult and places it in tmp.
Actually we're using substring replacement here with replacement string missing. Syntax for substring replacement is ${string//substring/replacement} (this replaces all occurrences of substring with replacement).

count=$(((${#CommandResult} - ${#tmp}) / ${#InstanceId}))

This gives us the number of occurrences of $InstanceId in $CommandResult.
${#string} gives string length so (${#CommandResult} - ${#tmp]) is length of all occurrences of $InstanceId (remember, we removed all occurrences of $InstanceId from $CommandResult and placed the result in $tmp).
Then we just divide the substraction with length of $InstanceId to get the number of $InstanceId occurrences.

For further info about substring replacement and string length, see e.g. https://www.tldp.org/LDP/abs/html/string-manipulation.html.