Hi dale

In shell scripting nowadays we define and reuse functions. Sections are no longer possible.

I would recommend starting with beginners literature on «bash scripting» and to advance from there.
A quick search brought up: https://linuxhandbook.com/bash/

On 14 Jun 2025, at 05:44, Dale <[email protected]> wrote:

[…]

In the old Basic days with Vic-20 puters, we had goto to
move from one part of a program to another. No idea on bash tho.

[…]

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Hey Dale,

On Fri, 13 Jun 2025 22:44:05 -0500
Dale <[email protected]> wrote:

Howdy,

As most know, I ordered some books about writing scripts.  A couple
things are not making sense to me.  Yet.  This is the basics of a
script I want to write. 

Section one.  See if a encrypted partition is open or not.  I use cryptsetup to open/close.
If open, print that it is open then go to mount part of script in
section two. 
If not open, ask for pass phrase and confirm it is open.  Then go to
section two.
Section one done, or fi.

Section two.  Is unencrypted file system mounted. 
If mounted, print that it is mounted and exit. 
If not mounted, mount and confirm mount and then exit.  If mount
fails, print error. 
Section two done, or fi. 

Here's the thing I can't figure out.  Let's say the I need section one
to go to section two at a certain point, maybe because the encrypted
file system is already open as shown above, how do I tell it to skip
to section two? 

Shell doesn't have 'goto's, but there are many control structures
available instead, the most important being ifs, loops (while, for),
and functions to avoid repeating common code. So try to structure
what you want in terms of those.

In this case, what you wrote above already translates pretty much
exactly to what you would need in a script. Something like:

if <already open>; then # but replace "<already open>", see below
# ...print already open...
else
# ...unlock the partition, check for error...
fi

if mountpoint -q /mnt/foo; then
# ...print already mounted...
else
# ...mount, check for error...
fi

The 'if's already include skipping parts of the code you don't want to
run; they just also enforce that execution continues downward :).

Also, if something goes bad, how do I tell it to print out that
something went wrong and stop? 

echo "Error: Couldn't do X."
exit 1

Every program (e.g. your script) exits with a numeric code 0-255 for
the calling program (e.g. the shell) to inspect. Convention is that 0
means success and any non-zero number indicates some type of error
(which is up to the program itself to decide, so you can pick
whatever). So "exit [some nonzero number]" is how you stop and
indicate failure. "exit 0" would indicate success.

This error code is also how you can check for failure of cryptsetup
and mount. If they return a zero code, great! If not, then we should
abort.

There are a few ways to write this. After each command, the shell
sets a special variable "$?" to the command's exit code. So we could
be explicit about it:

cryptsetup open ...
if [[ $? -ne 0 ]]; then
echo "Error: Couldn't unlock disk."
exit 1
fi

However, we can also write this more directly, because what 'if'
*does* is check whether the command after the 'if' returns zero or not
(and the '!' inverts the check to mean 'run if the command failed',
rather than 'run if the command succeeded'):

if ! cryptsetup open ...; then
echo "Error: Couldn't unlock disk."
exit 1
fi

You can repeat the "is it open" or "is it mounted" checks after the
calls to cryptsetup or mount if you like, but typically one would just
rely on the exit status.

The book I'm reading is Linux command:  Advanced methods and
strategies to shell scripting by William Vance.  I don't know who the
guy is but it is the one with the newest copyright date.  2020.  It's basically the same info as all the other books which still has me
clueless on the above info.  In the old Basic days with Vic-20
puters, we had goto to move from one part of a program to another.
No idea on bash tho. 

Also, someone posted about mountpoint -q.  That will help with section two.  Is there a way to find out if a file system is open using
cryptsetup or some other command that I can put in a script? 

cryptsetup creates a symlink under /dev/mapper with the target name of
the device you opened, so you could check for existence of that device
(e.g. /dev/mapper/sda3_crypt or whatever it's called for you).

if [[ -e /dev/mapper/sda3_crypt ]]; then

Maybe this will get me started.  Then I get to write a lot of scripts
for each drive or drive set.  o_O 

Thanks. 

Dale

:-)  :-) 

Hope this helps,
Bryan

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Am Fri, Jun 13, 2025 at 10:44:05PM -0500 schrieb Dale:

Howdy,

As most know, I ordered some books about writing scripts.  A couple
things are not making sense to me.  Yet.  This is the basics of a script
I want to write. 

If you have a script with many sections that depend on one another, you can write it as one long script, or to make it more digestible when you read it
a few years later, put blocks of code into functions and then call those functions from the main scope, like so:

check_prereqs() {
...
}

do_stuff() {
...
}

cleanup() {
...
}

# main scope: call the above functions
check_prereqs
do_stuff
cleanup


To get flow control, it is common to have early return on error. That means: as soon as you encounter a problem that your script cannot handle, have the script exit. This is preferable over nested if-else-structures.

You can take it to the extrem with the statement `set -e`. This causes the script to terminate as soon as any of its commands returns != 0 unhandled. That means if you want the script to continue, you need to “catch” any possible error case yourself with `if` or a || construct, as in:
mountpoint /some/path || echo "/some/path is not a mountpoint."

The disadvantage: the script becomes more verbose.
The advantage: you might discover bugs that you never thought of and you
make the script safer.

Section one.  See if a encrypted partition is open or not.  I use cryptsetup to open/close.
If open, print that it is open then go to mount part of script in
section two. 

Pseudo code for the first section:

if check_container_is_open then
print "container is open"
else
open_container
if not check_container_is_open then
print "Failed to open container."
exit
fi
print "container is now open"
fi

Note that I did not put the last print into an else. Because if the script encountered the problem case, it would have exited anyways.

If not open, ask for pass phrase and confirm it is open.  Then go to
section two.
Section one done, or fi.

Section two.  Is unencrypted file system mounted. 
If mounted, print that it is mounted and exit. 
If not mounted, mount and confirm mount and then exit.  If mount fails, print error. 
Section two done, or fi. 

Here's the thing I can't figure out.  Let's say the I need section one
to go to section two at a certain point, maybe because the encrypted
file system is already open as shown above, how do I tell it to skip to section two? 

As others mentioned, put the sections into functions, call the functions in sequence and let the functions return early if necessary.

Also, if something goes bad, how do I tell it to print out that
something went wrong and stop? 

I tend to define a function called die in all my scripts that require an
early exit on error:

die() {
print "$@" > /dev/stderr
exit 1
}

Then, instead of a print, you simply put this into the script:
die "LUKS container could not be opened."

The book I'm reading is Linux command:  Advanced methods and strategies
to shell scripting by William Vance.  I don't know who the guy is but it
is the one with the newest copyright date.  2020.  It's basically the
same info as all the other books which still has me clueless on the
above info.  In the old Basic days with Vic-20 puters, we had goto to
move from one part of a program to another.  No idea on bash tho. 

Also, someone posted about mountpoint -q.  That will help with section two.  Is there a way to find out if a file system is open using
cryptsetup or some other command that I can put in a script? 

lsblk comes to mind. I guess it just reads internal data from /sys or /dev
and puts it into a nice readable form.

frank@q ~ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
loop0 7:0 0 102,9M 1 loop /mnt/data/audio/sid/hvsc/C64Music nvme0n1 259:0 0 1,8T 0 disk
├─nvme0n1p1 259:1 0 300M 0 part /boot
├─nvme0n1p2 259:2 0 16M 0 part
├─nvme0n1p3 259:3 0 195,2G 0 part /mnt/windows
└─nvme0n1p4 259:4 0 1,6T 0 part
└─root 253:0 0 1,6T 0 crypt
├─vg-root 253:1 0 50G 0 lvm /
├─vg-home 253:2 0 200G 0 lvm /home
├─vg-gentoo 253:3 0 50G 0 lvm /mnt/gentoo
└─vg-data 253:4 0 1,3T 0 lvm /mnt/data

To make parsing easier, you can define the colums to display yourself. Then only output type and mointpoints, grep for lines beginning with crypt (to
not catch lines that have “crypt” in the mountpoint) and lastly grep for the
mountpoint, if needed:

lsblk --option-for-your-columns | grep ^crypt | grep "$YOUR_MOUNTPOINT"

--
Grüße | Greetings | Salut | Qapla’
Please do not share anything from, with or about me on any social network.

If I wanted to sit in a Mercedes Benz, I’d call for a taxi.

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Am Tue, Jul 01, 2025 at 06:50:40PM -0500 schrieb Dale:

OK.  I got one wrote, sort of.
[…]
This is the script.  Tell me what I did wrong.  Please be kind.  This is the first real script I've ever done. 

I’ll share some of my bash wisdom. Some may be nitpicks, others a matter of personal taste.

#/bin/bash

# Define the mount point
MOUNT_POINT="/home/dale/Desktop/Crypt"
LVM_DEV="/dev/vg.crypt/crypt"

lsblk -o NAME -o LABEL | grep ^crypt-open > /dev/null

-------------------------------------------^^^^^^^^^^^^
grep has a -q option to suppress output, no redirection necessary.

if [ "$?" -eq "0" ] ; then

The `if $?` part is actually kinda nicely readable, but you could of course also do a direct `if lsblk | grep; then`.

    echo "Crypt file system is open"

    else echo "Crypt is not open.  Please enter passphrase."

------^^^^^^^^^
Lol, it never occured to me that `else` may be followed by a command without semicolon, because I’ve always written it on its own line. It is however common practice to put the else on the same level of indentation as its respective `if` and `fi`.

    cryptsetup open $LVM_DEV crypt
fi

# Check if the disk is already mounted
if mountpoint -q "$MOUNT_POINT"; then
    echo "The disk is already mounted at $MOUNT_POINT."
    # mount if not mounted
    else mount $MOUNT_POINT
    exit 0
fi

Same thing here with the `else` indentation. It is not visible on first
sight that there is an if/else/fi structure here. And it’s not immediately clear that the exit also belongs into the else block.

This is simple still but hey, I'm new at this.  It does work on one part
of it at least.  ROFL 

Tool tip: shellcheck. It will give all sorts of feedback on common pitfalls and give suggestions on improvements. For instance, it showed me something I overlooked (you wrote #/bin/bash instead of #!/bin/bash).

--
Grüße | Greetings | Salut | Qapla’
Please do not share anything from, with or about me on any social network.

Electronically yours

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On 7/1/25 8:47 PM, Dale wrote:

Lol, it never occured to me that `else` may be followed by a command without
semicolon, because I’ve always written it on its own line. It is however >> common practice to put the else on the same level of indentation as its
respective `if` and `fi`.

Well, this part of the script may not have been executed yet.  Keep in
mind, the device is open and mounted so it only runs the first bit, I
guess it ignores the rest.  I may be wrong tho.  Does it need to be on
its own line?  I'm learning, trying to anyway.  May as well learn it right.  LOL 

"else" doesn't need to be on its own line but people almost universally
do so because it makes it easier to read.



if [ "$?" -eq "0" ] ; then
echo "Crypt file system is open"
else
echo "Crypt is not open. Please enter passphrase."
cryptsetup open $LVM_DEV crypt
fi


This makes your eyes get drawn to the lines that are aligned left, which
have the "when shall I run it?" logic. You can easily tell that
"cryptsetup open" happens AFTER the "else".


--
Eli Schwartz

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