mjhjmtu

Ubuntu 18.04 server + LXDE. I can't get the hang of this bash scripting.

This is my script "start" (with line numbering):

#!/bin/bash
reply=sudo mount 192.168.0.2:/home/dk/NFS /home/dk/NFS
if $reply == 0
then 
 echo "NFS mounted OK"
else 
 echo "Mounting NFS failed: $reply"
fi

reply=sudo mount LABEL="60GB" /home/dk/60GB
if $reply == 0
then 
 echo "60GB mounted OK"
else 
 echo "Mounting 60GB failed: $reply"
fi
exit 0

This is the result of running it:

$ ./scripts/start
mount: only root can do that
./start: line 3: ==: command not found
Mounting NFS failed: 
mount: only root can do that
./start: line 11: ==: command not found
Mounting 60GB failed: 
$ 

• Why did it ignore the sudo before mount?


• Why did it not consider if to be a command ?


• Why did it not print the (non-zero) value of $reply?

Well you're assigning output of a command incorrectly. Should be:

reply=$(sudo mount 192.168.0.2:/home/dk/NFS /home/dk/NFS)

That's called command substitution. Sometimes you see it in old Bourne shell syntax with backquotes instead of $(...), but that's not recommended nowadays because backquotes can't be nested easily, while you can do nested $( cmd1 $(cmd2))

Why did it not consider "if" to be a command?

If statements operate on commands, but what you give is variable $reply, which only exists temporarily ( see later in the answer about that) so it exists only for mount command's environment, but the shell running the script knows nothing of it - it doesn't exist. To compare strings use [, and yes it's a command also known as test. So do

if test "$reply" == 0

See quotes? That's important, otherwise if there's spaces, shell will expand variable to two or more separate entities not one.

But if you want to check exit status of command, just do

if mount 192.168.0.2:/home/dk/NFS /home/dk/NFS

See no sudo? That's because it's usually redundant to use sudo in script multiple times. Just call script itself with sudo and all commands will have root privilege.

I'd also say echo is redundant because mount command already can print errors to terminal, but if you want custom message, you can do

if mount 192.168.0.2:/home/dk/NFS /home/dk/NFS 1> /dev/null
then
 echo "Success"
else
 echo "Fail"
fi

Because of 1> normal output is suppressed (actually redirected to /dev/null especially for that purpose) but errors will show if anything goes wrong.

Why did it ignore the "sudo" before "mount" ?

As for why you're getting error message that's because the form

reply=sudo mount 192.168.0.2:/home/dk/NFS /home/dk/NFS

is treated as envvariable=value command arg1 arg2, i.e. you're putting variable result with value sudo into environment of mount command. The command will know about it, but after command exits - the variable is gone too.

Why did it not print the (non-zero) value of $reply?

Because reply doesn't store exit status as explained before. There's actually a variable for that provided by shell already, $? so use that as

if [ $? -eq 0 ] 

Rinse and repeat the suggestions for other statements in your script.

Good luck