LinuxQuestions.org - [SOLVED] defensive Bash scripting

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defensive Bash scripting

Hi guys,

How do i start off my Bash script to check to see if the file im interested in(which is automatically generated by another service) is actually there and if not there how can i tell the it to stop the execution of the rest of the script and echo something like file or directory not found? in BASH.

Thanks in advance!

Code:

-- test (use in a shell script to check to see if a given statement is true) 

-- case ... in .. esac (use in a shell script to perform separate actions for a variety of cases)

-- break (use in a shell script to skip the rest of the commands in the loop and restart at the beggining of the loop

-- sleep 5s (pause for 5 seconds)

-- continue (use in a for, while, until, or select loop to stop the current iteration and start the next one

Code:

if [[ ! -f filename ]]; then

  echo "file not found"

  exit 1

fi

see "man test" also :)

Code:

if [[ -f filename ]]; then

echo "Got it yo!"

else

{

  echo "Not yet dude" 

  exit 1

}

fi

that way you know either way. ;)

That's done your homework for you!!

of course I (we, others) have to take into account you may not know anything about programming whatsoever.

Introduction

Quote:

Originally Posted by Waris (Post 5719398)

Hi Waris and once again welcome to LQ.

You have done some bash scripting, as shown in your other question http://www.linuxquestions.org/questi...9/#post5718425, therefore I urge you to post your code here, or better describe what you have reviewed or tried.

As I mentioned in that other thread, here are a few bash reference links:
Bash Guide for Beginners
Advanced BASH Scripting Guide
My Bash Blog

Note that in Bash Beginners guide will tell you lots about file tests for things like making a determination as to whether a file exists and if it is a regular file or a directory. Please take the time to review these or other references for Bash.

I feel that if you persist with asking open ended questions, you'll possibly get confusing information back with members sometimes attempting to provide you wish some potentially useful code clips.

Quote:

Originally Posted by BW-userx (Post 5719466)

Code:

if [[ -f filename ]]; then

echo "Got it yo!"

else

{

  echo "Not yet dude" 

  exit 1

}

fi

that way you know either way. ;)

I saw that also. But I punted and guessed that suicidaleggroll only gave him "half" on purpose.
I did workup this exercise for shits and giggles.

Code:

touch LQRocks

if [[ ! -f LQRocks ]] ; then echo "Not found"; else echo Exists  ; fi

rm LQRocks

if [[ ! -f LQRocks ]] ; then echo "Not found"; else echo Exists  ; fi

I don't think I said too much because he still needs to figure out what (besides the shebang and whatnot) in order to get that to work in that if statement?

Quote:

Originally Posted by Habitual (Post 5719610)

I saw that also. But I punted and guessed that suicidaleggroll only gave him "half" on purpose.
I did workup this exercise for shits and giggles.

Code:

touch LQRocks

if [[ ! -f LQRocks ]] ; then echo "Not found"; else echo Exists  ; fi

rm LQRocks

if [[ ! -f LQRocks ]] ; then echo "Not found"; else echo Exists  ; fi

yours too can be changed to this.

Code:

[[ ! -f LQRocks ]] && echo "Not found"  || (echo Exists ; rm LQRocks)

or

[[ ! -f LQRocks ]] && echo "Not found" || echo "Exists"

which is not full proof programming in BASH because BASH does not have an ternary operator - but if the coder knows what he is working with he can get away with that. Depending on the circumstances.

Note:
why you got rm LQrocks when it returns that it is not there I do not know. of if it is then what takes place by the way you have it written?

@rtmistler

Oh I didn't realize it was that guy. I just looked at the link you gave to that page to reference his other post .... I don't find myself paying attention to the poster name, I look more at the problem presented.

Thank you guys for your responses. greatly appreciate it. This is a huge community and i am very happy for that. Also, rtMistler, I will post in the right forums. Sorry beginners mistake.

thanks again guys!!!

Quote:

Originally Posted by suicidaleggroll (Post 5719428)

Code:

if [[ ! -f filename ]]; then

  echo "file not found"

  exit 1

fi

This was exactly what i was looking for. Thank you. But what i cant understand is what is the ! and -f for? I am very new to the whole scripting world.:D

Quote:

Originally Posted by Waris (Post 5719658)

This was exactly what i was looking for. Thank you. But what i cant understand is what is the ! and -f for? I am very new to the whole scripting world.:D

Logical Not !
File test operators
Exit and Exit Status

Quote:

Originally Posted by suicidaleggroll (Post 5719428)

Code:

if [[ ! -f filename ]]; then

  echo "file not found"

  exit 1

fi

This was exactly what i was looking for. Thank you. But what i cant understand is what is the ! and -f for? I am very new to the whole scripting world.:D

Quote:

Originally Posted by BW-userx (Post 5719660)

Logical Not !
File test operators
Exit and Exit Status

Thanks! This is pretty straight forward! gracias compadres!