# blkid --uuid 2026-01-19-03-28-45-00
/dev/sdc
Meaning that the block device with that UUID is connected to the system.

When this executes,

destination="2026-01-19-03-28-45-00";
printf "destination=$destination\n";
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then
printf "destination device not connected. Aborting.\n"
else
printf "destination device is connected.\n"
dev="$( blkid --uuid $destination )";
printf "dev=$dev\n";
# FTH;
fi;

this is the output.
destination=2026-01-19-03-28-45-00
destination device not connected. Aborting.

With the device being present, I expect this. destination=2026-01-19-03-28-45-00
destination device is connected.
dev=/dev/sdc

Does this line have a syntax error?
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then

Thanks, ... P.

--
mobile: +1 778 951 5147
VoIP: +1 778 508 0020
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projects: en.wikibooks.org/wiki/User:PeterEasthope

--- PyGate Linux v1.5.5
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

* peter@easthope.ca <peter@easthope.ca> [26-01/24=Sat 21:12 -0700]:

# blkid --uuid 2026-01-19-03-28-45-00
/dev/sdc
Meaning that the block device with that UUID is connected to the system.

When this executes,

destination="2026-01-19-03-28-45-00";
printf "destination=$destination\n";
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then
printf "destination device not connected. Aborting.\n"
else
printf "destination device is connected.\n"
dev="$( blkid --uuid $destination )";
printf "dev=$dev\n";
# FTH;
fi;

this is the output.
destination=2026-01-19-03-28-45-00
destination device not connected. Aborting.

With the device being present, I expect this. destination=2026-01-19-03-28-45-00
destination device is connected.
dev=/dev/sdc

Does this line have a syntax error?
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then

The syntax is correct but the logic is confusing. Try this:

$ PS1='$?\$ '
0$ blkid --uuid 473f5ac6-f392-488c-b51f-1798531db64a
/dev/vda2
0$ blkid --uuid 473f5ac6-f392-488c-b51f-1798531db64aXXXX
2$ isConnectedUUID(){ lsblk -alno UUID|grep "$1" >/dev/null;}
0$ isConnectedUUID 473f5ac6-f392-488c-b51f-1798531db64a
0$ isConnectedUUID 473f5ac6-f392-488c-b51f-1798531db64aXXXX
1$ if isConnectedUUID 473f5ac6-f392-488c-b51f-1798531db64a;then echo OK;else echo OOPS;fi
OK
0$

--- PyGate Linux v1.5.5
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 2026-01-24, peter@easthope.ca wrote:

Does this line have a syntax error?
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then

As say Will you could use a function to clarify your code and it is
better to protect your variables. Also you could use "grep -qs" and
remove "> /dev/null". And you could use only blkid and not lsblk. But
this do not answer your question. I try your code and it works here so
the problem is elsewhere.
Do you run bash or sh ?
Could you provide us
type -a blkid
type -a lsblk
type -a grep

--- PyGate Linux v1.5.5
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

peter@easthope.ca writes:

# blkid --uuid 2026-01-19-03-28-45-00
/dev/sdc

Is this a real uuid or redacted one? Its syntax is strange for me.

Meaning that the block device with that UUID is connected to the system.

When this executes,

destination="2026-01-19-03-28-45-00";
printf "destination=$destination\n";
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then
printf "destination device not connected. Aborting.\n"
else
printf "destination device is connected.\n"
dev="$( blkid --uuid $destination )";
printf "dev=$dev\n";
# FTH;
fi;

this is the output.
destination=2026-01-19-03-28-45-00
destination device not connected. Aborting.

With the device being present, I expect this. destination=2026-01-19-03-28-45-00
destination device is connected.
dev=/dev/sdc

Does this line have a syntax error?
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then

Thanks, ... P.

what returns:
destination="2026-01-19-03-28-45-00";
lsblk -alno UUID | grep $destination
?
KJ

--
http://wolnelektury.pl/wesprzyj/teraz/
EMACS = Each Manual's Audience is Completely Stupified

--- PyGate Linux v1.5.5
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Sat, Jan 24, 2026 at 21:12:48 -0700, peter@easthope.ca wrote:

destination="2026-01-19-03-28-45-00";
printf "destination=$destination\n";

Never put expansions in the first argument of printf. That argument
is interpreted by printf, with characters like % and \ being special.
What you want is:

printf 'destination=%s\n' "$destination"

if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then

Error 1: "$destination" must be quoted.

Error 2: With no options, grep will treat the first non-option
argument as a Basic Regular Expression, which I don't think is what
you want. Use the -F option to treat it as a plain string.

Error 3: Use the -- option terminator in case the argument begins with
a "-" character.

Also, you may replace "grep >/dev/null" with grep -q.

Finally, the parentheses are not needed.

Thus:

if ! lsblk -alno UUID | grep -qF -- "$destination"; then
printf 'not connected...'

You could also use "case" (sh) or "[[" (bash) to get rid of the grep altogether. With case, you would need to reverse the order of the
checks, with the positive (connected) case first:

#!/bin/sh
case $(lsblk -alno UUID) in
*"$destination"*) printf 'connected...' ;;
*) printf 'not connected...' ;;
esac

With [[ you may continue checking for the negative first:

#!/bin/bash
if [[ $(lsblk -alno UUID) != *"$destination"* ]]; then
printf "not connected..."

My personal preference would be to check the positive case first,
regardless of which approach you use, because it removes a negation,
making the code easier to read and understand.

dev="$( blkid --uuid $destination )";

The quotes you've used are optional. The quotes around "$destination"
are required.

dev=$( blkid --uuid "$destination" )

or

dev="$( blkid --uuid "$destination" )"

printf "dev=$dev\n";

Same as before: use %s in the format argument and "$dev" (quoted!) as
a second argument. That's the only way to print the content *exactly*
as is, with no interpretation.

this is the output.
destination=2026-01-19-03-28-45-00
destination device not connected. Aborting.

With the device being present, I expect this. destination=2026-01-19-03-28-45-00
destination device is connected.
dev=/dev/sdc

Without seeing the output of lsblk -alno UUID we can't help any further.

Does this line have a syntax error?
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then

No, just the 3 errors that I listed earlier.

--- PyGate Linux v1.5.5
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

Hello again,

From a private message,
I modified your script slightly and it works for me.

Thanks.

The drive isn't formatted and has a UUID such as
2026-01-19-03-28-45-00. Shorter than a UUID for a file system.

After reading the reply I noticed that the UUID had changed. It's
revised periodically. After writing? Elapsed time is involved? I
don't understand in detail.

UUID isn't a time-invariant identity for the drive. Two external
drives here are the same model. Serial number might identify.

Revised the code listed yesterday. Now similar to this.

printf "destination is the serial number of a LaCie HDD connected by USB.\n"; destination="10000E000D959403";
printf 'destination=%s\n' "$destination";
if ! lsblk -o SERIAL | grep -F -- "$destination" > /dev/null ;
then
printf "destination device not connected ";
printf "or the serial number is wrong. Aborting.\n";
else
printf "destination device is connected.\n"
dev= lsblk --nodeps -o name,serial | grep -F -- "$destination" | cut -d ' ' -f1 ;
printf 'dev=%s is ready to receive backup.\n' "$dev";
printf "Press any key to continue.\n";
read -n 1 c;
FTH;
fi;

OK in a simple test. Suggestions always welcome. Something may be
more efficient than the long pipeline.
lsblk --nodeps -o name,serial | grep -F -- "$destination" | cut -d ' ' -f1

As happens too often, I was looking in the wrong place. Thanks for
the reply.

Thx, ... P.


--
mobile: +1 778 951 5147
VoIP: +1 778 508 0020
Bcc: peter at e a s t h o p e dot c a
projects: en.wikibooks.org/wiki/User:PeterEasthope

--- PyGate Linux v1.5.5
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Sun, Jan 25, 2026 at 11:54:37 -0700, peter@easthope.ca wrote:

The drive isn't formatted

What?

and has a UUID such as
2026-01-19-03-28-45-00. Shorter than a UUID for a file system.

This looks like a timestamp.

OK in a simple test. Suggestions always welcome. Something may be
more efficient than the long pipeline.
lsblk --nodeps -o name,serial | grep -F -- "$destination" | cut -d ' ' -f1

It would help if we knew what the output looks like. On my system:

hobbit:~$ sudo lsblk --nodeps -o name,serial
[sudo] password for greg:
NAME SERIAL
nvme0n1 UPJQD01ZTJ03L4

So... you *have* the serial number (somehow) and you *want* the "name"
field? The obvious way would be to use awk:

lsblk --nodeps -o name,serial |
awk -v serial="$serial" '$2 == serial {print $1}'

On my system:

hobbit:~$ serial=UPJQD01ZTJ03L4
hobbit:~$ sudo lsblk --nodeps -o name,serial | awk -v serial="$serial" '$2 == serial {print $1}'
nvme0n1

awk -v isn't 100% safe with all inputs, but if your serial number is
reasonable (alphanumeric, maybe with some basic punctuation, but no
backslashes or control characters) it should be OK.

--- PyGate Linux v1.5.5
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Sun, Jan 25, 2026 at 11:54:37AM -0700, peter@easthope.ca wrote:

Hello again,

From a private message,
I modified your script slightly and it works for me.

Thanks.

The drive isn't formatted and has a UUID such as
2026-01-19-03-28-45-00. Shorter than a UUID for a file system.

After reading the reply I noticed that the UUID had changed. It's
revised periodically. After writing? Elapsed time is involved? I
don't understand in detail.

UUID isn't a time-invariant identity for the drive. Two external
drives here are the same model. Serial number might identify.

Revised the code listed yesterday. Now similar to this.

OK, since you asked for them, some stylistic comments
(I didn't reply in the first round since I couldn't come
up with an idea on what was actually failing and didn't
want to distract from the main question)
Comments inline:

printf "destination is the serial number of a LaCie HDD connected by USB.\n"; destination="10000E000D959403";
printf 'destination=%s\n' "$destination";

# You quoted "$destination" and moved it to the right spot in printf: good

if ! lsblk -o SERIAL | grep -F -- "$destination" > /dev/null ;
then
printf "destination device not connected ";
printf "or the serial number is wrong. Aborting.\n";
else
printf "destination device is connected.\n"
dev= lsblk --nodeps -o name,serial | grep -F -- "$destination" | cut -d ' ' -f1 ;
printf 'dev=%s is ready to receive backup.\n' "$dev";
printf "Press any key to continue.\n";
read -n 1 c;
FTH;
fi;

You worked in the suggestions elsethread, that's good. Especially the
quoting of "$destination" was a timebomb -- once the string contains
a space the script would stop working mysteriously, years after it
had been working. That "--" is similar: once $destination starta with
a dash, things go south. And so on.
One difficult thing in shells, when you come from other languages,
is to wrap one head's around variable substitution (and the other
expansions). The variable is expanded textually in place, it is not
a "placeholder". So
if ! lsblk -o SERIAL | grep -F -- $destination > /dev/null
(without the quotes) is first converted into
if ! lsblk -o SERIAL | grep -F -- 10000E000D959403 > /dev/null
Then, the command lsblk is invoked, and its result piped to
"grep -F -- $10000E000D959403 > /dev/null", for "if" to act on its
exit code. This would work, mind you. Now, if the value of destination
suddenly changes to
destination="1000 0E00 0D95 9403", the "if" line is first expanded
to
if ! lsblk -o SERIAL | grep -F -- 1000 0E00 0D95 9403 > /dev/null
...and the grep would see those unexpected arguments 0E00, 0D95 and
9403 (unexpected for us: for grep they would be just extra file names
to work on), so in the best case you'd get:
grep: 0E00: No such file or directory
grep: 0D95: No such file or directory
grep: 9403: No such file or directory
I wrote "best case" because, of course, you might have some files
named like that lying around: then, your script's behaviour starts
to get /really/ strange :-)
Another suggestion, more aesthetic: the semicolons at the end of
the lines are unnecessary. You only need one when putting two
lines together (as a replacement for a newline). For a reader of
your script they are confusing.
(A place where you might see it is in the construction
if <condition> ; then
do this
...
But you already separated the "if" and "then" by a newline, which
is perfectly fine, too.
Cheers
--
tom s


--- PyGate Linux v1.5.6
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Sun, Jan 25, 2026 at 12:30?AM <peter@easthope.ca> wrote:

# blkid --uuid 2026-01-19-03-28-45-00
/dev/sdc
Meaning that the block device with that UUID is connected to the system.

When this executes,

destination="2026-01-19-03-28-45-00";
printf "destination=$destination\n";
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then
printf "destination device not connected. Aborting.\n"
else
printf "destination device is connected.\n"
dev="$( blkid --uuid $destination )";
printf "dev=$dev\n";
# FTH;
fi;

this is the output.
destination=2026-01-19-03-28-45-00
destination device not connected. Aborting.

With the device being present, I expect this. destination=2026-01-19-03-28-45-00
destination device is connected.
dev=/dev/sdc

Does this line have a syntax error?
if ! ( lsblk -alno UUID | grep $destination > /dev/null ); then

You should run your script through Shellcheck. It will tell you about the obvious problems, like quoting variables.
Jeff


--- PyGate Linux v1.5.6
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Sunday, January 25, 2026 5:12:48 AM CET, peter@easthope.ca wrote:

# blkid --uuid 2026-01-19-03-28-45-00
/dev/sdc
Meaning that the block device with that UUID is connected to the system.

why not just do something like:

dev="$( blkid --uuid "$destination" )"
if [[ $? -eq 0 ]]
then
echo "destination device is connected."
echo "dev=$dev"
else
echo "destination device not connected. Aborting."
fi

am i missing something?

greetings...

--- PyGate Linux v1.5.6
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

From: Jeffrey Walton <noloader@gmail.com>
Date: Mon, 26 Jan 2026 07:37:31 -0500

You should run your script through Shellcheck. It will tell you about the obvious problems, like quoting variables.

Thanks Jeffrey. Wasn't aware of Shellcheck and will look.

Several functions are declared in a file invoked with ". file" at the end of .bashrc.

Thx, ... P.

--
mobile: +1 778 951 5147
VoIP: +1 778 508 0020
Bcc: peter at e a s t h o p e dot c a
projects: en.wikibooks.org/wiki/User:PeterEasthope

--- PyGate Linux v1.5.6
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Mon 26 Jan 2026 at 08:02:34 (+0100), tomas@tuxteam.de wrote:

Another suggestion, more aesthetic: the semicolons at the end of
the lines are unnecessary. You only need one when putting two
lines together (as a replacement for a newline). For a reader of
your script they are confusing.

I agree with the aesthetics, but readers might as well get used to
at least /seeing/ them, as type-ing a function adds them back in.

(A place where you might see it is in the construction

if <condition> ; then
do this
...

But you already separated the "if" and "then" by a newline, which
is perfectly fine, too.

And as it happens, type will turn:

if <condition>
then

into:

if <condition>; then

anyway. Ah well.

Cheers,
David.

--- PyGate Linux v1.5.6
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

From: Greg Wooledge <greg@wooledge.org>
Date: Sun, 25 Jan 2026 15:26:19 -0500

What?

My knowledge of ISO 9660 is cursory but note the first sentence
in https://en.wikipedia.org/wiki/Optical_disk_image ,
"... disk image ... written to an optical disk, disk sector by disc sector ...".
Not directly comparable to ext4.

2026-01-19-03-28-45-00. Shorter than a UUID for a file system.

This looks like a timestamp.

Explained by Thomas Schmitt in <16912500410373272277@scdbackup.webframe.org>

lsblk --nodeps -o name,serial | grep -F -- "$destination" | cut -d ' ' -f1

So... you *have* the serial number (somehow) ...

As you did.
# lsblk --nodeps -o name,serial

The obvious way would be to use awk: ...

OK, thanks. cut, awk and others. cut seemed straightforward.

awk -v isn't 100% safe with all inputs, but if your serial number is reasonable (alphanumeric, maybe with some basic punctuation, but no backslashes or control characters) it should be OK.

The cut I used relied only on blank separation.

Thanks, ... P.

--
mobile: +1 778 951 5147
VoIP: +1 778 508 0020
Bcc: peter at e a s t h o p e dot c a
projects: en.wikibooks.org/wiki/User:PeterEasthope

--- PyGate Linux v1.5.6
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)