simple bash script erro

[jmd9qs]

hi all,

recently started learning how to create scripts. while messing around with a "script" i've made, i have run into a simple error. here's the script:


#! /bin/bash
who | wc -l >$users;
echo "There are currently $users users logged in"
~

i get this error:


{03-01-09 - 07:51 PM User: j}~$ nusers
/home/j/bin/nusers: line 2: $users: ambiguous redirect
There are currently users logged in
{03-01-09 - 07:51 PM User: j}~$

i know i'm overlooking something really simple here... any help? i've googled the "ambiguous redirect" and haven't found much to go off of...

[asmoore82]

you can't assign variable values with the `$` structure - that's only for getting the values they hold.

assign them with a `=` structure and no `$` at all

the other missing link you need is how to capture the output of the commands in the variable;
`>` is only for redirecting output to files.

For variables and assignment statements, this ability is called command substitution
and there are 2 forms of it that do exactly the same thing.
1. the single backquotes - this is the old fashioned way that is more widely
supported by different shells - you will see more often, especially in system startup scripts:

variable=`cmd arg1`
2. modern BASH style - this is easier on the eyes but will not work in older versions of shells:

variable="$( cmd arg1 )"

so, your corrected code would look like this:

#!/bin/bash
users="$( who | wc -l )"
echo "There are currently $users users logged in."

[Omnios]

I just ran that it said there are two users logged in.

Umm?

[jmd9qs]

wow... quick and precise. thank you for clearing that up!

[asmoore82]

I just ran that it said there are two users logged in.

Umm?

it counted you twice:


~$ who | wc -l
2
~$ who
asmoore tty7 2009-02-26 16:59 (:0)
asmoore pts/0 2009-03-01 22:07 (:0.0)

if we really wanted to be fancy and not count ppl more than once:

who | cut -d" " -f1 | sort | uniq | wc -l

[asmoore82]

super-duper shell scripting fun:
http://ubuntuforums.org/showthread.php?t=1078472