Shell scripting help (bash) - Tilted Forum Project Discussion Community

Silvy · 02-26-2004, 02:55 AM

Hi,

I have the following problem:
I would like a script to decide on a commandline that should be executed.
This descision is based on the arguments passed to the script.
The possibilities for the commandline-to-be-executed are fixed, and declared at the beginning of the script.

script flow:
- declaration of possible command calls (CALL_A and CALL_B , see below)
- case statement on the argument $1 that either sets (CALL=CALL_A or CALL=CALL_B)
- exectute CALL

This works fine in most cases, except when CALL_A or CALL_B use an output re-director.
If I declare CALL_A="ls -al >test.txt"
then ls is executed with "-al" and ">test.txt" as parameters, causing an error because ls can't find the file ">test.txt".

I realize this might sound fuzzy, so I wrote 2 scripts as an example:

Script 1:
(echo's all arguments that were passed to it. this allows you to see how the commandline was interpreted.)

Code:

#!/bin/bash 
#prints the first 4 arguments that are passed to it.  $0 is the name of the script!
#
if [ -n $0 ]
then
   echo "arg 0: $0" 
fi
if [ -n $1 ] then
   echo "arg 1: $1" 
fi 
if [ -n $2 ] then
   echo "arg 2: $2" 
fi 
if [ -n $3 ] then   
  echo "arg 3: $3" 
fi 
if [ -n $4 ] then 
   echo "arg 4: $4" 
fi

Script 2:
(This script is giving me troubles, it runs the above script with normal or redirected output commandlines. The second type should echo into a file and not on screen.)

Code:

## testing script

#command to run:
CALL_A="./arg_check 1st 2nd 3rd 4th"
CALL_B="./arg_check 1st >result.txt"

#select command based on argument, or present helpful message:
if [ -n "$1" ]  #test wether $1 has been initialized
then
  case "$1" in
  "a" ) CALL=$CALL_A ;;
  "b" ) CALL=$CALL_B ;;
  * ) echo "Duh, enter a or b"
      exit 1 ;;
  esac
else
  echo "Enter a or b as an argument please"
  exit 1;
fi

#call the chosen command:
$CALL

If you copy/save these scripts as "arg_check" and "testscript" respectively, you can run "./testscript a" or "./testscript b" to see the results. (remember to chmod +x them both)

You'll notice that the CALL_B commandline if executed directly on the prompt behaves as expected: the output of "arg_check a" is redirected to "result.txt"

I'd REALLY like to know what in the second script I should change to get the expected result: i.e.
./testscript a results in output to screen
./testscript b results in output to file

Note: It's not really an option to remove the declarations and "$CALL" statement, and move the commandlines directly into the case statement (which would work irf you used "backticks": `) as the script this is meant for uses several sources and checks to build and conditionally execute the commands.

2nd note: I'm quite new to shell scripting so if you have any tips, please post them! Also if this code is laughable: any constructive comments are really appreciated!

EDIT: edited because the "submit" button is a lot more attractive than the one for "preview"

mgcloud · 02-26-2004, 07:52 AM

You might like this site if you haven't come across it already: http://tldp.org/LDP/abs/html/

I'm kind of a newbie too (haven't had *any* time to start learning recently), but it seems like you've forgotten the #!/bin/bash on your "testscript" file. That may fix the problem.

Silvy · 02-26-2004, 04:31 PM

That was exactly the site that helped me this far, but for finding a specific answer I think it's a little chaotic...
But to be honest, I haven't read it from the beginning, I just glance at the subjects I need.

I couldn't find an example or answer to my problem in that document, but I realise it's not something you'd come across often.

And yes, I did forget to add the "shabang" line in my script, it was the haste. Adding it made no difference though.

Thanks for the help, but the problem still stands. Anyone?

mgcloud · 02-26-2004, 08:53 PM

Hi,

Try replacing your last line with eval $CALL
(instead of $CALL)

Silvy · 02-27-2004, 12:16 AM

Quote:

Originally posted by mgcloud
Try replacing your last line with eval $CALL
(instead of $CALL)

Thanks a lot! That was exactly it!

Cheers!

02-26-2004, 02:55 AM	#1 (permalink)
Silvy paranoid Location: The Netherlands	Shell scripting help (bash) Hi, I have the following problem: I would like a script to decide on a commandline that should be executed. This descision is based on the arguments passed to the script. The possibilities for the commandline-to-be-executed are fixed, and declared at the beginning of the script. script flow: - declaration of possible command calls (CALL_A and CALL_B , see below) - case statement on the argument $1 that either sets (CALL=CALL_A or CALL=CALL_B) - exectute CALL This works fine in most cases, except when CALL_A or CALL_B use an output re-director. If I declare CALL_A="ls -al >test.txt" then ls is executed with "-al" and ">test.txt" as parameters, causing an error because ls can't find the file ">test.txt". I realize this might sound fuzzy, so I wrote 2 scripts as an example: Script 1: (echo's all arguments that were passed to it. this allows you to see how the commandline was interpreted.) Code: #!/bin/bash #prints the first 4 arguments that are passed to it. $0 is the name of the script! # if [ -n $0 ] then echo "arg 0: $0" fi if [ -n $1 ] then echo "arg 1: $1" fi if [ -n $2 ] then echo "arg 2: $2" fi if [ -n $3 ] then echo "arg 3: $3" fi if [ -n $4 ] then echo "arg 4: $4" fi Script 2: (This script is giving me troubles, it runs the above script with normal or redirected output commandlines. The second type should echo into a file and not on screen.) Code: ## testing script #command to run: CALL_A="./arg_check 1st 2nd 3rd 4th" CALL_B="./arg_check 1st >result.txt" #select command based on argument, or present helpful message: if [ -n "$1" ] #test wether $1 has been initialized then case "$1" in "a" ) CALL=$CALL_A ;; "b" ) CALL=$CALL_B ;; * ) echo "Duh, enter a or b" exit 1 ;; esac else echo "Enter a or b as an argument please" exit 1; fi #call the chosen command: $CALL If you copy/save these scripts as "arg_check" and "testscript" respectively, you can run "./testscript a" or "./testscript b" to see the results. (remember to chmod +x them both) You'll notice that the CALL_B commandline if executed directly on the prompt behaves as expected: the output of "arg_check a" is redirected to "result.txt" I'd REALLY like to know what in the second script I should change to get the expected result: i.e. ./testscript a results in output to screen ./testscript b results in output to file Note: It's not really an option to remove the declarations and "$CALL" statement, and move the commandlines directly into the case statement (which would work irf you used "backticks": `) as the script this is meant for uses several sources and checks to build and conditionally execute the commands. 2nd note: I'm quite new to shell scripting so if you have any tips, please post them! Also if this code is laughable: any constructive comments are really appreciated! EDIT: edited because the "submit" button is a lot more attractive than the one for "preview" __________________ "Do not kill. Do not rape. Do not steal. These are principles which every man of every faith can embrace. " - Murphy MacManus (Boondock Saints) Last edited by Silvy; 02-26-2004 at 03:00 AM..

02-26-2004, 04:31 PM	#3 (permalink)
Silvy paranoid Location: The Netherlands	That was exactly the site that helped me this far, but for finding a specific answer I think it's a little chaotic... But to be honest, I haven't read it from the beginning, I just glance at the subjects I need. I couldn't find an example or answer to my problem in that document, but I realise it's not something you'd come across often. And yes, I did forget to add the "shabang" line in my script, it was the haste. Adding it made no difference though. Thanks for the help, but the problem still stands. Anyone? __________________ "Do not kill. Do not rape. Do not steal. These are principles which every man of every faith can embrace. " - Murphy MacManus (Boondock Saints)

02-26-2004, 07:52 AM	#2 (permalink)
mgcloud Upright	You might like this site if you haven't come across it already: http://tldp.org/LDP/abs/html/ I'm kind of a newbie too (haven't had any time to start learning recently), but it seems like you've forgotten the #!/bin/bash on your "testscript" file. That may fix the problem.

02-26-2004, 08:53 PM	#4 (permalink)
mgcloud Upright	Hi, Try replacing your last line with eval $CALL (instead of $CALL)