Check if a user is logged on

[maff20]

Hello folks,

i am using this piece of code to check if a user is logged on to the system or not;

#! /bin/sh


echo -n "Please enter the username to check->"
read username

if who | grep $username
then
:
else
echo "'$username' is not currently logged in";
fi

exit 0

My problem is that if am to enter a user id of less than 3 characters it is returning a posative result even if that user id does not exist, whats going on? I should mention that i am a total noob.....

[scathefire]

perhaps you should try this instead:

#!/bin/bash
echo -n "User: "
read -e username
TEST=`who | awk '{print $1}' | grep -x $username`
if [ -z "$TEST" ];then
echo "Not here"
else
echo "Here"
fi

[maff20]

cheers for the help, though im not sure i understand the code......

why would my current code be returning false positives? i have tested the program a little further and it would appear to work fine with numbers above 33. When 33 or anything below that number is entered i get a false positive.

[scathefire]

when you run your command in the terminal what does it look like? when you do a grep the way you are doing its going to look for patterns, not exact matches.

[scathefire]

perhaps you should try this instead:

#!/bin/bash
echo -n "User: "
read -e username
TEST=`who | awk '{print $1}' | grep -x $username`
if [ -z "$TEST" ];then
echo "Not here"
else
echo "Here"
fi

Explained by line number

2) echo and do not output trailing newline
3) use readline to place the input into variable called username
4) define a variable whose value is the total output of the commands inside the tick marks.
4a) run who, use awk to grab the first string value it comes to, which is a space separated line, and grep for exact match for the value that is username.
5) if the value of $TEST is null, the we can assume the user is not logged on.
7) else we assume the user is here

[maff20]

Here is my complete code.

Thanks greatly for breaking down your example code, not many would take the time to do that

I shall try to make sense of it after i have my dinner