How to debug shell script?

George2 · 02-19-2006, 11:22 PM

Hello everyone,

I am using RedHat Shrike 9.0. I am wondering how to debug shell script, for example, step-by-step debug to watch the outputs of each line of command.

thanks in advance,
George

alunduil · 02-20-2006, 12:13 AM

It's as simple as adding this line to the beginning of your file:

Code:

set -x

Regards,

Alunduil

alienDog · 02-20-2006, 07:09 AM

or changing

Code:

#!/bin/bash

to

Code:

#!/bin/bash -x

provided it's bash script.

You can also run the script with:

Code:

bash -x [yourscript]

from the commandline.

George2 · 02-20-2006, 08:48 PM

Alunduil,

Quote:

Originally Posted by alunduil

It's as simple as adding this line to the beginning of your file:

Code:

set -x

Regards,

Alunduil

Do you mean this command can enable shell script to run step-by-step (like the step-next feature of an IDE, for example, F6 in Eclipse in debug mode)? I have tried and it only prints out the commands (including output of command) contained in the script file and a sign '+' before each command.

regards,
George

George2 · 02-20-2006, 08:53 PM

alienDog,

Quote:

Originally Posted by alienDog

or changing

Code:

#!/bin/bash

to

Code:

#!/bin/bash -x

provided it's bash script.

You can also run the script with:

Code:

bash -x [yourscript]

from the commandline.

I have tried both methods you mentioned. Do you mean this command can enable shell script to run step-by-step (like the step-next feature of an IDE, for example, F6 in Eclipse in debug mode)? I have tried and it only prints out the commands (including output of command) contained in the script file and a sign '+' before each command.

regards,
George

alienDog · 02-21-2006, 08:08 AM

Quote:

Originally Posted by George2

alienDog,
I have tried both methods you mentioned. Do you mean this command can enable shell script to run step-by-step (like the step-next feature of an IDE, for example, F6 in Eclipse in debug mode)? I have tried and it only prints out the commands (including output of command) contained in the script file and a sign '+' before each command.
regards,
George

Yes, printing them is what it does. I don't think it's possible to run commands "step by step" with bash, but I'll look into it and get back to you.

alienDog · 02-21-2006, 08:36 AM

Yep. It not possible with default bash. What I'd suggest is placing a 'read' command to the points where you want the execution to pause. This way the execution stops at that point until you hit enter. You could also consider echoing something appropriate to screen at the certain points of the screen.

Code:

command1
command2
...
echo "Debug message #1 [hit enter to continue]"
read
command3
command3
...
echo "Debug message #2 [hit enter to continue]"
read

It will ease finding errors, though it's not the same as being able to execute the scripts step by step. More help on debugging here:

http://www.tldp.org/LDP/Bash-Beginne...ect_02_03.html

You might also want to take a look at separate bashdb debugger:

http://bashdb.sourceforge.net/bashdb.html

For that you will need bash 3.0 or later (you probably have that already, bash --version will tell).

George2 · 02-21-2006, 10:24 PM

alienDog,

Quote:

Originally Posted by alienDog

Yep. It not possible with default bash. What I'd suggest is placing a 'read' command to the points where you want the execution to pause. This way the execution stops at that point until you hit enter. You could also consider echoing something appropriate to screen at the certain points of the screen.

Code:

command1
command2
...
echo "Debug message #1 [hit enter to continue]"
read
command3
command3
...
echo "Debug message #2 [hit enter to continue]"
read

It will ease finding errors, though it's not the same as being able to execute the scripts step by step. More help on debugging here:

http://www.tldp.org/LDP/Bash-Beginne...ect_02_03.html

You might also want to take a look at separate bashdb debugger:

http://bashdb.sourceforge.net/bashdb.html

For that you will need bash 3.0 or later (you probably have that already, bash --version will tell).

Your method works cool on my Linux desktop! But I can not open the first link you recommended. Can you open it now?

regards,
George

chrism01 · 02-21-2006, 10:32 PM

Personally I also use the -v switch like so:
set -xv
v => verbose

George2 · 02-21-2006, 11:49 PM

chrism01,

Quote:

Originally Posted by chrism01

Personally I also use the -v switch like so:
set -xv
v => verbose

I have tried your method and it works very cool!

regards,
George

trickykid · 02-22-2006, 12:44 AM

sh -x ./scriptname # also works..

alienDog · 02-22-2006, 09:09 AM

Quote:

Originally Posted by George2

alienDog,
Your method works cool on my Linux desktop! But I can not open the first link you recommended. Can you open it now?
regards,
George

Strange, it works fine for me? It's one of the linux documentation project pages, so it should work.

George2 · 02-22-2006, 07:30 PM

trickykid,

Quote:

Originally Posted by trickykid

sh -x ./scriptname # also works..

I have tried that your method works. Cool!

regards,
George

George2 · 02-22-2006, 07:32 PM

alienDog,

Quote:

Originally Posted by alienDog

Strange, it works fine for me? It's one of the linux documentation project pages, so it should work.

I have tried again but still can not access this URL. Too strange.

regards,
George

alienDog · 02-23-2006, 05:48 AM

Maybe contact your ISP?