Csdrhrt

I need to compare a command output with a string.
This is the scenario:

pvs_var=$(pvs | grep "sdb1") 

so pvs var is: /dev/sdb1 vg_name lvm2 a-- 100.00g 0

if [[ $($pvs_var | awk '{ print $2 }') = vg_name ]]; then

    do something

fi

The issue is that the output of the if statement is

-bash: /dev/sdb1: Permission denied

I don't understand this behavior.
Thank you

You are attempting to execute the contents of $pvs_var as a command, rather than passing the string to awk.

To fix this, add an echo or printf in your if statement:

if [[ $(echo "$pvs_var" | awk '{ print $2 }') = vg_name ]]; then

    do something

fi

Get the output in JSON format, and then you'll be able to extract information in a more reliable way:

pv_info=$(pvs -o pv_all,vg_all --unit b --nosuffix --reportformat json)

sdb1_vg=$(

  printf '%sn' "$pv_info" |

   jq -r '.report.pv|select(.pv_name == "/dev/sdb1").vg_name'

)



if [ "$sdb1_vg" = vg_name ]; then...

Or use a proper programming language with a JSON library instead of a shell (ksh93 does have JSON support though in its upcoming version).

If it's just that one query you want to do, pvs can also do all the work for you:

sdb1_vg=$(

  pvs -o vg_name -S pv_name=/dev/sdb1 --no-heading --config 'log{prefix=""}'

)

Also remember to quote your variables and avoid echo.

If you want to compare the VG from the output, then it might be easier to pre-process that:

# if you still need it

pvs_var=$(pvs | grep "sdb1") 

vg_name=$(pvs | grep "sdb1" | awk '{print $2}')

if [ "$vg_name" = "vg_name" ]; then

  echo do something

fi

What you were doing with

$($pvs_var | awk '{ print $2 }')

was initiating a command substitution $( ... ) whose first command was $pvs_var. Bash dutifully substituted the value of the variable and then attempted to execute it. That's not what you wanted.

Another alternative would be to send the variable as a here-string to the awk command:

# ...

if [ $(awk '{print $2}' <<< "$pvs_var") = "vg_name" ]; then

# ...

Here, the command substitution is calling awk and passing it input on stdin -- the contents of the $pvs_var variable.

You can try only with awk :

pvs | awk -v search='vg_name' '/sdb1/&&$2==search{exit 1}' || echo "ok"