how to display text when no output is available

[sidebrake]

I am running this command in my script to display the current logged in user:

data8=$(who | grep 'tty' | awk '{print $1,$2,$3,$4}')
label8='Current User :'
echo "${label8} ${data8}"

is there a way to display "no user" as the output if theres no current user logged in when i run this script?

[Cabhan]

Yes indeed.

Bash includes support for default values for a variable. They follow the format of:

${parameter:-default_value}

What this will do is return the value of $parameter if it is not blank, and default_value otherwise. Let's try it out:

tanya:~ alex$ msg=Hello; echo ${msg:-Goodbye}
Hello
tanya:~ alex$ msg=; echo ${msg:-Goodbye}
Goodbye

Do you see how to use this to solve your problem?

Also, if you're looking for more cool things to do in Bash, this is the best guide I have ever found:
http://tldp.org/LDP/abs/html/

This default value trick is found at:
http://tldp.org/LDP/abs/html/paramet...stitution.html

[sidebrake]

Yes indeed.

Bash includes support for default values for a variable. They follow the format of:

${parameter:-default_value}

What this will do is return the value of $parameter if it is not blank, and default_value otherwise. Let's try it out:

tanya:~ alex$ msg=Hello; echo ${msg:-Goodbye}
Hello
tanya:~ alex$ msg=; echo ${msg:-Goodbye}
Goodbye

Do you see how to use this to solve your problem?

I am not sure exactly how to incorporate this into the lines that I already have. Which is this:

data8=$(who | grep 'tty' | awk '{print $1,$2,$3,$4}')
label8='Current User :'
echo "${label8} ${data8}"

This is my output:

"Current User : john tty7 2008-09-16 08:25"

I just need whatever behind "Current User :" to say "no user" if there is no output to be display. Please advice, thanks.

[sidebrake]

so this is what i ended up using and it works:

data8=$(who | grep 'tty' | awk '{print $1,$2,$3,$4}')
label8='Current User :'
echo "${label8} ${data8:-no user}"

output:

"Current User : no user"

thanks for your help Cabhan