Cannot run "taskkill" on a bash script, but can run from cygwin

Question

I have a very simple Bash Script. The goal of this bash script is to take in a parameter of a port number, and kill all processes running on that port.

#!/bin/bash
PID_NUMBER=$(netstat -a -n -b -o | grep $1 | sed -e "s/[[:space:]]\+/ /g" | cut -d ' ' -f5)
echo "$PID_NUMBER"
taskkill /F /PID "$PID_NUMBER"

However, running the bash script in Cygwin echoes the PID_NUMBER, correctly, but throws an "ERROR: Invalid query" for taskkill

Output:

$ ./KillProcessesAtPort.sh 546
1540
ERROR: Invalid query

If I run "taskkill /F /PID 1540" in Cygwin, the process is sucessfully terminated.

$ taskkill /F /PID 1540
SUCCESS: The process with PID 1540 has been terminated.

I am running this script in Windows 10 on Cygwin terminal. Why does my script throw an ERROR for taskkill whereas just executing taskkill in Cygwin works?

Answer 1

Here's what worked for me:

#!/bin/bash
PID_NUMBER=$(netstat -a -n -b -o | grep $1 | sed -e "s/[[:space:]]\+/ /g" | cut -d ' ' -f6 | head -1)
echo "$PID_NUMBER"
taskkill /F /PID "$PID_NUMBER"

Note1: I had to replace -f5 with -f6 because otherwise I'd get a different column.
Note2: taskkill would fail with ERROR: Invalid query when more than one pid was returned. Solved by adding | head -1.

Conclusion1: Be aware that your solution is not robust: since netstat can output e.g. LISTENING before the pid you cannot reliably split the way you did.
Conclusion2: You should always pass a single value to taskkill, not a multiline string.

Suggestion: Differentiate for UDP and TCP, since TCP connections have a STATUS column:

PID_NUMBER=$(netstat -a -n -o | grep :$1 | awk '/UDP/{a=$4} /TCP/{a=$5} END{print a}')