Hi,

This shell function is a prototype.

Test() { \
workingVolume=40d81969-8f9d-4964-b214-87bcf273192a
echo "working volume asigned a value; now try blkid."
if ! blkid -t UUID="$workingVolume" > /dev/null; then
printf "workingVolume not found.\n"
else
printf "workingVolume found.\n"
fi
echo "Now try to catch the name of the device."
blkid -t UUID="$workingVolume" | cut -d':'
}

The if statement gives the result I expect.

I miss the syntax to make the last statement work.

Thx, ... P.



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--- PyGate Linux v1.5.18
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 01 Jul 2026 08:58:08 -0700
peter@easthope.ca wrote:

I miss the syntax to make the last statement work.

You might do better with lsblk. See the --list-columns and --output
options for ideas on how to do it.

--
Does anybody read signatures any more?

https://charlescurley.com
https://charlescurley.com/blog/

--- PyGate Linux v1.5.18
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Wed, Jul 01, 2026 at 08:58:08 -0700, peter@easthope.ca wrote:

Hi,

This shell function is a prototype.

Test() { \
workingVolume=40d81969-8f9d-4964-b214-87bcf273192a
echo "working volume asigned a value; now try blkid."
if ! blkid -t UUID="$workingVolume" > /dev/null; then
printf "workingVolume not found.\n"
else
printf "workingVolume found.\n"
fi
echo "Now try to catch the name of the device."
blkid -t UUID="$workingVolume" | cut -d':'
}

The if statement gives the result I expect.

I miss the syntax to make the last statement work.

Move the last two commands inside the "else ... fi" block, so they aren't executed when the working volume is not found.

hobbit:~$ blkid
hobbit:~$ sudo blkid
[sudo] password for greg:
/dev/nvme0n1p3: UUID="afdc7260-5289-4014-bc89-0fa3e843e334" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="599cd65f-67f9-400c-ad22-1c3ee95f5341"
/dev/nvme0n1p1: LABEL_FATBOOT="SYSTEM" LABEL="SYSTEM" UUID="2E5D-D8D4" BLOCK_SIZE="512" TYPE="vfat" PARTLABEL="EFI system partition" PARTUUID="3d23b4eb-5477-417b-9bc9-c2a6d263c2ed"
/dev/nvme0n1p4: LABEL="Windows RE Tools" BLOCK_SIZE="512" UUID="D47AB7687AB74650" TYPE="ntfs" PARTLABEL="Basic data partition" PARTUUID="bd4e5997-6d42-4f64-9c8b-812355b573bb"
/dev/nvme0n1p2: PARTLABEL="Microsoft reserved partition" PARTUUID="9ca2c59a-85fe-4602-9e1e-1937a59834a5"

It looks like what you were trying for was cut -d: -f1

--- PyGate Linux v1.5.18
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 01/07/26 at 19:16, Greg Wooledge wrote:

It looks like what you were trying for was cut -d: -f1

In addiction I'd suggest to use the so called "exit status variable: $?"
in the "if ; then" statement:

...
echo "working volume assigned a value; now try blkid."
blkid -t UUID="$workingVolume" >/dev/null 2>&1
if [ $? -ne 0 ] ; then
printf "workingVolume not found.\n"
else
...

it makes the code more readable, IMHO.

--
Franco Martelli

--- PyGate Linux v1.5.18
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Wed, Jul 01, 2026 at 20:40:30 +0200, Franco Martelli wrote:

In addiction I'd suggest to use the so called "exit status variable: $?" in the "if ; then" statement:

...
echo "working volume assigned a value; now try blkid."
blkid -t UUID="$workingVolume" >/dev/null 2>&1
if [ $? -ne 0 ] ; then
printf "workingVolume not found.\n"
else
...

it makes the code more readable, IMHO.

I disagree, but of course this is an opinion, and you're entitled to
feel this way.

In the general case where you want to run a command, and print an error
message of your own if it fails, inside of a function, I would probably
use this format:

checkvolume() {
local workingVolume=...
blkid -t UUID="$workingVolume" >/dev/null 2>&1 || {
echo "working volume not found" >&2
return 1
}
...
}

However, in this *specific* example, the OP is actually calling blkid
twice -- once to check whether it succeeds, then again to get the output
and parse it. I would reduce that to a single call instead. Then it
becomes more "interesting" to extract the exit status. Assuming we're
using bash, and not sh, we can use pipefail:

checkvolume() {
local workingVolume=...
local device
device=$(set -o pipefail;
blkid -t UUID="$workingVolume" 2>/dev/null | cut -d: -f1) || {
echo "working volume not found" >&2
return 1
}
printf "working volume found: device is '%s'\n" "$device"
...
}

Otherwise, if we're using sh, the best solution is probably to store
the full output of lsblk, and then parse it in a second pass. In fact,
this may even be preferred in bash.

checkvolume() {
# use local if your shell has it
workingVolume=...
device=$(blkid -t UUID="$workingVolume" 2>/dev/null) || {
echo "working volume not found" >&2
return 1
}
device=${device%%:*}
printf "working volume found: device is '%s'\n" "$device"
...
}

That's probably the cleanest version.

--- PyGate Linux v1.5.18
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)