CODEWITHSUNDEEP
linuxbashshell
Hamburml
Hamburml

Reputation: 345

Use bash variables in subsequent bash command

I am writing a bash script which shows me all tcp connections which are important for me. For that I use netstat -atp. It looks like this:

num_haproxy_443_established=$(netstat -atp | grep ESTABLISHED | grep :https | grep haproxy | wc -l)
printf "\n show ESTABLISHED connections port 443 \n"
printf " %s" $num_haproxy_443_established

In the bash script I have some of these calls and now I would like to optimize it and call netstat -atp only once and reuse the results. I tried:

netstat_res=$(netstat -atp)

num_haproxy_443_timewait=$("$netstat_res" | grep TIME_WAIT | grep :https | grep haproxy | wc -l)
printf " %s" $num_haproxy_443_timewait

After executing the script I always get 0: command not found as error message. How can I use a variable inside $(...) ?

Thanks!

Upvotes: 1

Views: 108

Answers (3)

anubhava
anubhava

Reputation: 784958

You can use shell array to store your netstat command:

# your netstat command
netstat_res=(netstat -atp)

# then execute it as
num_haproxy_443_timewait=$("${netstat_res[@]}" |
awk '/TIME_WAIT/ && /:TIME_WAIT/ && /haproxy/{++n} END{print n}')

echo $num_haproxy_443_timewait

Also note how you can avoid multiple grep calls by a single awk call.

Related BASH FAQ: I'm trying to put a command in a variable, but the complex cases always fail!

Upvotes: 1

m13r
m13r

Reputation: 2721

If you have something like A="foo" then $("$A") will be resolved to call the program foo in the subshell.

So you just have to echo the content of the variable and then grep from it:

num_haproxy_443_timewait=$(echo "$netstat_res" | grep TIME_WAIT ...)

Upvotes: 1

Raindy Long
Raindy Long

Reputation: 61

At your case, $netstat_res is the result but not the COMMAND, if you want to save the result and use it not only once, save the result to the file is the better way, such as:

    netstat -atp > /tmp/netstat_status.txt
    num_haproxy_443_timewait=$(cat /tmp/netstat_status.txt | grep TIME_WAIT | grep :https | grep haproxy | wc -l)
    printf " %s" $num_haproxy_443_timewait

Upvotes: 0

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