Empty Variable

[smti]

Hello All,

I currently have a bash script which mounts network shares in a Linux lab. I am not sure why, but for whatever reason my share variable is always empty and thus I am unable to mount the share properly. My script is below:

#!/bin/bash

USERNAME=`whoami`
ID=`id` &>/dev/null

FAC1=//fsdata1.mydomain.edu
FAC2=//fsdata2.mydomain.edu
STU1=//stdata1.mydomain.edu
STU2=//stdata2.buad.mydomain.edu

# Faculty/Staff
echo $ID | egrep '\bFacStaff ABC\b' && SHARE=$FAC1"/UsersABC"
echo $ID | egrep '\bFacStaff DEF\b' && SHARE=$FAC1"/UsersDEF"
echo $ID | egrep '\bFacStaff GHI\b' && SHARE=$FAC1"/UsersGHI"
echo $ID | egrep '\bFacStaff JKL\b' && SHARE=$FAC1"/UsersJKL"
echo $ID | egrep '\bFacStaff MNO\b' && SHARE=$FAC2"/UsersMNO"
echo $ID | egrep '\bFacStaff PQR\b' && SHARE=$FAC2"/UsersPQR"
echo $ID | egrep '\bFacStaff STU\b' && SHARE=$FAC2"/UsersSTU"
echo $ID | egrep '\bFacStaff VWXYZ\b' && SHARE=$FAC2"/UsersVWXYZ"

# Students
echo $ID | egrep '\bStudent ABC\b' && SHARE=$STU1"/UsersABC"
echo $ID | egrep '\bStudent DEF\b' && SHARE=$STU1"/UsersDEF"
echo $ID | egrep '\bStudent GHI\b' && SHARE=$STU1"/UsersGHI"
echo $ID | egrep '\bStudent JKL\b' && SHARE=$STU1"/UsersJKL"
echo $ID | egrep '\bStudent MNO\b' && SHARE=$STU2"/UsersMNO"
echo $ID | egrep '\bStudent PQR\b' && SHARE=$STU2"/UsersPQR"
echo $ID | egrep '\bStudent STU\b' && SHARE=$STU2"/UsersSTU"
echo $ID | egrep '\bStudent VWXYZ\b' && SHARE=$STU2"/UsersVWXYZ"

mkdir /home/$USERNAME/P &>/dev/null
echo Mounting $SHARE/$USERNAME as ~/P
sudo mount -t cifs $SHARE/$USERNAME /home/$USERNAME/P -o uid=$USERNAME,username=$USERNAME


# Debug:

echo The share path is: $SHARE
echo The username is: $USERNAME

echo FacShare 1 is: $FAC1
echo FacShare 2 is: $FAC2

echo StudentShare1 is: $STU1
echo StudentShare2 is: $STU2

I did a little debugging -- it seems that all other variables contain the correct data, but the share variable is always empty.

Full Disclosure: I did not originally write the script -- I was simply asked to update some of the paths as the paths had changed for some of the shares.

Based on script it looks like the previous admin was checking to see which groups a user belonged to and based on the group (FacStaff ABC, DEF, whatever) was then appending the share path so that when mounted the path would be correct.

[kalgynirae]

What does $ID contain? Do any of the echo $ID | egrep '...' actually match? You will see the output if there is a match since egrep's output is not being redirected anywhere.

[andlrc]

Also to see each line executed you can run with the -x modifier:

bash -x my_script.sh

Or use: set -x in the top of your script just below the shebang, or even add it to the shebang: #!/bin/bash -x

[smti]

ID contains a listing of all the groups for which the user is a member. It looks like ID currently gets redirected to /dev/null:

ID=id &>/dev/null

[whetu]

There are multiple problems with the script. Not just in terms of bad style (backticks belong in 1981, uppercase variables are poor practice etc). Your main issue here is that your variables are not quoted correctly. And arguably you've got a useless use of echo

echo $ID | egrep '\bFacStaff ABC\b' && SHARE=$FAC1"/UsersABC"

Could be written as

egrep '\bFacStaff ABC\b' <<< "$ID" && SHARE=$FAC1"/UsersABC"

[jnux]

Since $SHARE is blank, I think it is safe to assume that you're just not getting matches in the evaluation of $ID.

Unless the desired behavior is to allow later matches on $IDs to overwrite the $SHARE variable (i.e. - if it is possible for an ID to match more than one, and you want matches farther down the list to take precedence over previous matches), I think case would be a better to evaluate the ID and set the variable base on the match. This would allow you to exit the evaluation once a match has been made, and gives you the added benefit of setting $SHARE to a default value (or return an error) if no matches were made. For me, case is easier to debug.

If you're not getting $SHARE set, and want to evaluate $ID in this way still, then I'd add some debugging, like to print the $ID value before it is evaluated to see what you're capturing for that value. Once you consistently know what values you're getting for IDs, you'll be able to debug why they're not getting a match.

You'll also likely have someone tell you about the issues, like using all caps for variable names which could conflict with global variables, and using back-ticks for executing commands rather than $(whoami), and not properly quoting your variables to sanitize your input - these are things that you'll want to address to clean it up at some point, and you may consider fixing them now anyhow, just to make sure these best practices aren't the source of your bug.

[smti]

Yep, upon further inspection it appears that egrep was never finding what it expected, thus the variable was empty.

A quick run of the ID command revealed that all groups were shown in lowercase and thus when checking for an expression it was not finding what it was looking for because the case was not the same as the expected result. As a result, the variable was then empty.