Is there a awk command for searching if a user is logged on?

#! /bin/sh -

is_logged_in() {
  who | USER=$1 awk -v ret=1 '
    $1"" == ENVIRON["USER"]"" {ret = 0; exit}
    END {exit(ret)}'
}

if is_logged_in root; then
  echo root is logged in
fi

That defines a is_logged_in shell function, that takes a user name as argument. We feed the output of who to awk to which we've passed the function argument in the USER environment variable.

The awk code processes each record in turn. If the first field in the record is equal to the value of that environment variable (here appending "" to operands to force a string comparison), then we exit with a 0 (success) exit status.

That function can then be used in if statements to check whether a user is logged in.

Just an example of one of the possible ways to use awk and external commands:

is_logged($1) { print $1, "is present!"}

function is_logged(x,a){                     ## a local var
  "who|grep -w " x | getline a
  return a
}

And then:

$ awk -f test
abc
Darunia

--> Darunia is present!