How to match an exact string of digits with bash regular expression?

I'm trying to match and exact number with regex but It's only matching the first digit.

Here's a sample of the text I'm working with:

0x03600007  0 1206   km-Inspiron-3593 ~ : bash — Konsole
0x04c00002  0 15610  km-Inspiron-3593 Minecraft 1.7.10

And here's my code:

regex="^0x[0-9a-z]{8}[[:space:]]+-?[0-9][[:space:]]15610"
[[ $string =~ $regex ]] && echo "${BASH_REMATCH}"

I'm trying to get the value in the first column where the third column is a known value (15610 in this case). So the expression should match 0x04c00002 0 15610 (and I would capture first value from that) but it's only matching 0x03600007 0 1 (the remaining 4 digits are ignored).

For additional context, this text is the output of wmctrl -lp, first column is a window ID, second column is PID. So what I'm looking to extract is the window ID given a known PID.

I've tried things like \b (AFAIK this is for exact alphabetic word matches), brackets, quotes, no quotes.

Using awk

awk '$3 == 15610{print $1}' file
0x04c00002

Updated after OP's latest update:

regex="(0x[0-9a-z]{8})[ ]+0[ ]+15610[ ]+"

while read -r line; do echo "###### $line"; [[ "$line" =~ $regex ]] && typeset -p BASH_REMATCH; done < file

###### 0x03600007  0 1206   km-Inspiron-3593 ~ : bash — Konsole
###### 0x04c00002  0 15610  km-Inspiron-3593 Minecraft 1.7.10
declare -ar BASH_REMATCH=([0]="0x04c00002  0 15610  " [1]="0x04c00002")
                                                      ^^^^^^^^^^^^^^^^

Where:

• for the matching row we see BASH_REMATCH[0] matches the entire regex while ...
• BASH_REMATCH[1] matches the desired substring (ie, 1st column)

Or if we want to make sure the hex string is at the start of the line (and filter out the rest of the line):

regex="^(0x[0-9a-z]{8})[ ]+0[ ]+15610[ ]+.*$"                                                             

while read -r line; do echo "###### $line"; [[ "$line" =~ $regex ]] && typeset -p BASH_REMATCH; done < file

###### 0x03600007  0 1206   km-Inspiron-3593 ~ : bash — Konsole
###### 0x04c00002  0 15610  km-Inspiron-3593 Minecraft 1.7.10
declare -ar BASH_REMATCH=([0]="0x04c00002  0 15610  km-Inspiron-3593 Minecraft 1.7.10" [1]="0x04c00002")
                                                                                       ^^^^^^^^^^^^^^^^

Replacing the BASH_REMATCH approach with a comparison of columns:

regex="0x[0-9a-z]{8}"

while read -r line
do 
    echo "####### $line"
    read -r c1 c2 c3 rest_of_line <<< "$line"
    [[ "$c1" =~ $regex && "$c3" = "15610" ]] && echo "$c1"
done < file

####### 0x03600007  0 1206   km-Inspiron-3593 ~ : bash — Konsole
####### 0x04c00002  0 15610  km-Inspiron-3593 Minecraft 1.7.10
0x04c00002

# or

while read -r c1 c2 c3 rest_of_line
do   
    echo "####### $c1 $c2 $c3 $rest_of_line"
    [[ "$c1" =~ $regex && "$c3" = "15610" ]] && echo "$c1"
done < file

####### 0x03600007 0 1206 km-Inspiron-3593 ~ : bash — Konsole
####### 0x04c00002 0 15610 km-Inspiron-3593 Minecraft 1.7.10
0x04c00002

I think you've missed a repetition pattern. Using the first example:

0x03600007 0 1206 km-Inspiron-3593 ~ : bash — Konsole

with the provided regex:

original: `^0x[0-9a-z]{8}[[:space:]]+-?[0-9][[:space:]]`

first step: `^0x[0-9a-z]{8}[[:space:]]+` -> `0x03600007  `

second step: `-?` -> matches empty

third step: `[0-9][[:space:]]` -> `0 `

I'm guessing the extra digit came from the end of the regex, namely, the literal 15610.

If you want the full number, this regex might be better suited:

^0x[0-9a-z]{8}[[:space:]0-9]+[[:space:]]

Note the section [[:space:]0-9]+. If you only want the second number, you can probably make [0-9] be the only repetition. The regex I'm suggesting would allow you to continue your capture of the remaining of the text

regex="^0x[0-9a-z]{8}[[:space:]0-9]+[[:space:]]"
[[ "0x03600007  0 1206   km-Inspiron-3593 ~ : bash — Konsole" =~ $regex ]] && echo "${BASH_REMATCH}"