Shell Scripting Tutorial for Beginners 28 - How to debug a bash script Video Lecture | Complete Linux Course: Become a Linux Professional - Software Development

hey guys welcome to the next video on
shell scripting tutorial for beginners
in this video we will talk about
debugging our script using bash right so
sometimes when things don't go according
to the plan you need to determine what
exactly causes the script to fail and
bash provides extensive debugging
feature the most common is to start up
the sub shell with the minus X option
okay so there are some you know options
we can use to debug our script now this
is the script I have written in the last
video and this is nothing but just
looping around a while loop and printing
the value of count right and if any
error occurs if the error is - and if
the script run successfully
we are trapping this thing right this
signal right so this was the previous
script we were running now normally when
you run the script you can just run it
like this and it will execute you know
perfectly fine and you need don't need
to do anything but sometimes sometimes
you forgot for example this parenthesis
and when I run the script once again I
can see the error right so this time
it's pretty straightforward and it's a
syntax error so it's a syntax error near
unexpected token done which is on line
11 so 11 is here right and the problem
is here but we are pretty close because
the problem is in the while loop right
so it's pretty close so bash will give
you the you know error and even line
number where the problem is coming but
if you want to debug more you
and use this minus X option so you can
run the script with this and then you
just need to give for example bash - X
option right so just write bash - X and
the name of your script and then press
Enter
and now you will be able to you know see
more both operations so you can see what
happens first
the file is declared and then the trap
is set and then the pre ID is created so
PID is printed so whatever you know
steps or commands are executed in
sequence is going to print all of it
right so you can see now we are in the
you know this while loop and then the
sleep of 10 second comes and then you
know the counter is increased and then
the you know value of count is printed
right so whatever steps are happening
it's printing everything so in this way
whenever some problems occurs you will
be straightaway be aware that your
script is not working according to the
plan and the problem is coming from here
okay so this is one option you can use
to debug your script so what is the
option option is let me clear the
terminal and the option is bash - X and
then the name of your script so it will
run your script with this debug option
and it's going to give you step by step
what's happening in your script okay now
there is the similar option in your bash
script also you can apply here so
instead of writing minus X here for
example you want to run this script like
this and you don't want to use in the
command line minus X right so how you
can use this debugging inside your
script so
what you need to do is you need to use
the set option okay
so set option can be given like this so
first of all you can write minus X at
the top here also so after this
hash-bang bin bash when you write minus
X here then when you run the script it
will give you the similar you know
output okay
so you can use minus X option at the top
here also okay so this is one way of
using minus X the other way was using
the terminal right and let me show you
the another way of using this minus X
which is by using the set option so you
can do set minus X and then it will
start your debugging from the point
where you set minus X okay so what is
set minus X so set minus at X activates
debugging from the point it's written
right so from here
activate debugging now there is one more
option which is set loss X so you can
just write set plus X at any point in
the script so just try it like this and
it deactivates or stop your debugging
from this point wherever plus X is set
okay so let me run the script once again
and let's see what happens so you can
see for two lines until the line six we
saw this kind of you know debugging and
then the script is running normally okay
so it's not going to show you the you
know debugging output kind of a thing
okay so this is also how you can debug
your script so there are basically three
ways I have shown you one is by
using Bosch minus X and then the script
name of your script you can directly
give in the terminal debugging option
and then it will run fine other is by
just adding minus X at the top after
shabang bin forward slash bash and then
this option then the editing option will
be activated and by using the set minus
X which starts the debugging from this
point and set plus X which stop the
debugging at the point where it's
written okay so these are some of the
debugging options you can use in your
bash scripting I hope you have enjoyed
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and bye for now