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Umount: target is busy to variable

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0

I want to check if a USB is busy and store the result in a variable:

$ foo=$(umount /dev/sdb1)

$ umount: /path/mounted: target is busy.

But when I want to print $foo, I get an empty variable

$ echo $foo

$

My final goal is to umount the USB. If the target is busy, issue a warning to the user, using whiptail. So:

$ [[ -z $foo ]] || whiptail --msbox "Cancel the operation that is maintaining your USB busy" 0 0

Is it possible to store the error target is busy on a variable, or should I use another kind of technique?

shell-script variable variable-substitution error-handling unmounting

share|improve this question

edited 12 mins ago

G-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

asked 42 mins ago

guillermo chamorroguillermo chamorro

71611 silver badge1313 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  umount /dev/sdb1 || whiptail should work.
  
  – jordanm
  35 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @jordanm Thanks, it seems that works
  
  – guillermo chamorro
  30 mins ago
  

  
  
  
  

add a comment | 

0

I want to check if a USB is busy and store the result in a variable:

$ foo=$(umount /dev/sdb1)

$ umount: /path/mounted: target is busy.

But when I want to print $foo, I get an empty variable

$ echo $foo

$

My final goal is to umount the USB. If the target is busy, issue a warning to the user, using whiptail. So:

$ [[ -z $foo ]] || whiptail --msbox "Cancel the operation that is maintaining your USB busy" 0 0

Is it possible to store the error target is busy on a variable, or should I use another kind of technique?

shell-script variable variable-substitution error-handling unmounting

share|improve this question

edited 12 mins ago

G-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

asked 42 mins ago

guillermo chamorroguillermo chamorro

71611 silver badge1313 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  umount /dev/sdb1 || whiptail should work.
  
  – jordanm
  35 mins ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @jordanm Thanks, it seems that works
  
  – guillermo chamorro
  30 mins ago
  

  
  
  
  

add a comment | 

I want to check if a USB is busy and store the result in a variable:

$ foo=$(umount /dev/sdb1)

$ umount: /path/mounted: target is busy.

But when I want to print $foo, I get an empty variable

$ echo $foo

$

My final goal is to umount the USB. If the target is busy, issue a warning to the user, using whiptail. So:

$ [[ -z $foo ]] || whiptail --msbox "Cancel the operation that is maintaining your USB busy" 0 0

Is it possible to store the error target is busy on a variable, or should I use another kind of technique?

shell-script variable variable-substitution error-handling unmounting

share|improve this question

edited 12 mins ago

G-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

asked 42 mins ago

guillermo chamorroguillermo chamorro

71611 silver badge1313 bronze badges

$ foo=$(umount /dev/sdb1)

$ umount: /path/mounted: target is busy.

$ echo $foo

$

$ [[ -z $foo ]] || whiptail --msbox "Cancel the operation that is maintaining your USB busy" 0 0

share|improve this question

edited 12 mins ago

G-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

asked 42 mins ago

guillermo chamorroguillermo chamorro

71611 silver badge1313 bronze badges

share|improve this question

edited 12 mins ago

G-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

asked 42 mins ago

guillermo chamorroguillermo chamorro

71611 silver badge1313 bronze badges

edited 12 mins ago

G-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

edited 12 mins ago

G-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

asked 42 mins ago

guillermo chamorroguillermo chamorro

71611 silver badge1313 bronze badges

asked 42 mins ago

guillermo chamorroguillermo chamorro

71611 silver badge1313 bronze badges

1 Answer
1

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oldest

votes

1

Programs commonly write error messages to the “standard error” I/O stream;
“stderr” for short. 
If you search for that term, you’ll gets millions of results;
the short explanation is that stderr exists so error messages can and will
go to the screen when the “standard output” (“stdout”) is redirected,
as in a hypothetical command like

umount /dev/sdb1 > um.result.txt

And you can see this happening; the error message appears on your screen
even though you are trying to capture it in a variable.

The equally short answer is to use 2>&1
to merge the stderr stream into the stdout stream, so

foo=$(umount /dev/sdb1 2>&1)

will capture the error message in the variable.

Another approach, as suggested by jordanm in a comment,
is to look at the exit status. 
Variations on this theme include:

umount /dev/sdb1  ||  complain to user

if ! umount /dev/sdb1

then

    complain to user

fi

umount /dev/sdb1 2> /dev/null  ||  complain to user

 foo=$(umount /dev/sdb1 2>&1)  ||  complain to user using "$foo"

share|improve this answer

edited 16 mins ago

answered 27 mins ago

G-ManG-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

add a comment | 

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1

Programs commonly write error messages to the “standard error” I/O stream;
“stderr” for short. 
If you search for that term, you’ll gets millions of results;
the short explanation is that stderr exists so error messages can and will
go to the screen when the “standard output” (“stdout”) is redirected,
as in a hypothetical command like

umount /dev/sdb1 > um.result.txt

And you can see this happening; the error message appears on your screen
even though you are trying to capture it in a variable.

The equally short answer is to use 2>&1
to merge the stderr stream into the stdout stream, so

foo=$(umount /dev/sdb1 2>&1)

will capture the error message in the variable.

Another approach, as suggested by jordanm in a comment,
is to look at the exit status. 
Variations on this theme include:

umount /dev/sdb1  ||  complain to user

if ! umount /dev/sdb1

then

    complain to user

fi

umount /dev/sdb1 2> /dev/null  ||  complain to user

 foo=$(umount /dev/sdb1 2>&1)  ||  complain to user using "$foo"

share|improve this answer

edited 16 mins ago

answered 27 mins ago

G-ManG-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

add a comment | 

1

Programs commonly write error messages to the “standard error” I/O stream;
“stderr” for short. 
If you search for that term, you’ll gets millions of results;
the short explanation is that stderr exists so error messages can and will
go to the screen when the “standard output” (“stdout”) is redirected,
as in a hypothetical command like

umount /dev/sdb1 > um.result.txt

And you can see this happening; the error message appears on your screen
even though you are trying to capture it in a variable.

The equally short answer is to use 2>&1
to merge the stderr stream into the stdout stream, so

foo=$(umount /dev/sdb1 2>&1)

will capture the error message in the variable.

Another approach, as suggested by jordanm in a comment,
is to look at the exit status. 
Variations on this theme include:

umount /dev/sdb1  ||  complain to user

if ! umount /dev/sdb1

then

    complain to user

fi

umount /dev/sdb1 2> /dev/null  ||  complain to user

 foo=$(umount /dev/sdb1 2>&1)  ||  complain to user using "$foo"

share|improve this answer

edited 16 mins ago

answered 27 mins ago

G-ManG-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

add a comment | 

Programs commonly write error messages to the “standard error” I/O stream;
“stderr” for short. 
If you search for that term, you’ll gets millions of results;
the short explanation is that stderr exists so error messages can and will
go to the screen when the “standard output” (“stdout”) is redirected,
as in a hypothetical command like

umount /dev/sdb1 > um.result.txt

And you can see this happening; the error message appears on your screen
even though you are trying to capture it in a variable.

The equally short answer is to use 2>&1
to merge the stderr stream into the stdout stream, so

foo=$(umount /dev/sdb1 2>&1)

will capture the error message in the variable.

Another approach, as suggested by jordanm in a comment,
is to look at the exit status. 
Variations on this theme include:

umount /dev/sdb1  ||  complain to user

if ! umount /dev/sdb1

then

    complain to user

fi

umount /dev/sdb1 2> /dev/null  ||  complain to user

 foo=$(umount /dev/sdb1 2>&1)  ||  complain to user using "$foo"

share|improve this answer

edited 16 mins ago

answered 27 mins ago

G-ManG-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

umount /dev/sdb1 > um.result.txt

foo=$(umount /dev/sdb1 2>&1)

umount /dev/sdb1  ||  complain to user

if ! umount /dev/sdb1

then

    complain to user

fi

umount /dev/sdb1 2> /dev/null  ||  complain to user

 foo=$(umount /dev/sdb1 2>&1)  ||  complain to user using "$foo"

share|improve this answer

edited 16 mins ago

answered 27 mins ago

G-ManG-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

answered 27 mins ago

G-ManG-Man

15.3k99 gold badges4444 silver badges8484 bronze badges

answered 27 mins ago

G-ManG-Man

15.3k99 gold badges4444 silver badges8484 bronze badges