Novice needs Bash help.

manwithaplan · 02-25-2009, 06:09 AM

I cannot seem to figure out why I cant execute "top" or "nano" is this test script. Feedback much welcome.

It seems my value of $C always breaks and doesn't execute my command.

Code:

#!/bin/bash
clear
echo "Testing this script"
echo
echo "1-   top"
echo "2-   nano"
echo
echo "Select either (1-2) and press Enter:"
while read C && test "$C" \!= "1" -a "$C" \!= "2"; do
  case $C in
      1)
           top   
          clear && break ;;
      2)                                                   
           nano
         clear && break ;;       
     *)
         clear && echo "That's not one of the choices, try again"
       echo ;;
  esac
done

Newbie in Training....

acid_kewpie · 02-25-2009, 06:26 AM

what's the point of all that "test" stuff? just remove it.

manwithaplan · 02-25-2009, 06:57 AM

First off, I wanted to test the value of $C, and if its not equal to 1 or 2 then print an error message.

I'm very new too this... using man's and tutorials. So I'm testing 'while' loops in scripts for menus, before I put them into another script.

Then use $C variable further down the script, to wait for an input to execute a command using 'case'.

Is there an alternative to using 'test'?

Again I'm very new to this... so forgive the ignorance

acid_kewpie · 02-25-2009, 07:02 AM

well you've already got a working test in the *) option. that's the point of the case statement, right? I've never seen additional commands between a while and a do, suprised it works at all personally, but if it did work your logic is backwards, that test will only be true if C is NOT 1 or 2, therefore those 1) and 2) clauses can logically never be reached.

bigearsbilly · 02-25-2009, 07:05 AM

Code:

select choice in top nano;
do
    echo $choice
    break
done

Code:

dos?1.sh
1) top
2) nano
#? 2
nano

manwithaplan · 02-25-2009, 07:22 AM

Your right it doesn't work... it seems test doesnt support '*' wildcards, like in a case statement.

I changed it:

Code:

#!/bin/bash
clear
echo "Testing this script"
echo
echo "1-   top"
echo "2-   nano"
echo
echo "Select either (1-2) and press Enter:"
while read C && test "$C" \!= "1" -a "$C" \!= "2"; do
   clear && echo "That's not one of the choices, try again"
done
  case $C in
      1)
           top   
          clear && break ;;
      2)                                                   
           nano
         clear && break ;;       
   esac

It seems I'm way limited to adding additional choices. e.g. 3,4,5,6,7,8,9

bigearsbilly:

Perfect, I changed it too:

Code:

  select choice in top nano;
do
  $choice
    break
done

Though I need to add a menu with extra print

acid_kewpie · 02-25-2009, 07:30 AM

no no, just nuke the test statement, and use a PROPER case statement.

Code:

#!/bin/bash
clear
echo "Testing this script"
echo
echo "1-   top"
echo "2-   nano"
echo
echo "Select either (1-2) and press Enter:"
while read C ; do
  case $C in
      1)
           top   
          clear && break ;;
      2)                                                   
           nano
         clear && break ;;      
     *)
         clear && echo "That's not one of the choices, try again"
         echo ;;
   esac
done

manwithaplan · 02-25-2009, 07:49 AM

Quote:

no no, just nuke the test statement, and use a PROPER case statement.

Bravo, this saves alot of time. Thank you

BTW: What really is 'test' used for?

acid_kewpie · 02-25-2009, 08:49 AM

test is a slightly odd tool, as it is used to evaluate statements, but normally in line with other structured commands, like if and while. test is also called by [ which allows the format of a test query to look much more like a standard logic statement:

if test $a -eq b
then
...
fi

can be changed to

if [ $a -eq b ]
then
...
fi

which probably looks more self explanatory, but here [ is actually a symbolic link to the test command itself. clever little trick basically.

manwithaplan · 02-25-2009, 09:36 AM

acid_kewpie I was looking @ your PROPER case, and noticed that it kept creating a line in my menu as it returned and didnt clear the selected number off the screen

e.g.

Code:

  Testing this script"

    "1-   top"
    "2-   nano"
  
  "Select either (1-2) and press Enter

   1

   2

   4

   etc...

So I used the [ ] "the clever little trick" and tried this to return the menu:

Code:

#!/bin/bash
clear
C=0
while [ $C -eq 0 ]; do
echo "Testing this script"
echo
echo "1-   top"
echo "2-   nano"
echo
read -p "Select either (1-2) and press Enter:  " C
 case $C in
      1)
           top   
          clear && break ;;
      2)                                                   
           nano
         clear && break ;;      
     *)
         clear
           C=0 ;;
   esac
done

This automatically reset C=0 and returns to the menu when an incorrect choice is chosen.

the_ultimate_samurai · 02-25-2009, 02:58 PM

Quote:

Originally Posted by acid_kewpie

test is a slightly odd tool, as it is used to evaluate statements, but normally in line with other structured commands, like if and while. test is also called by [ which allows the format of a test query to look much more like a standard logic statement:

if test $a -eq b
then
...
fi

can be changed to

if [ $a -eq b ]
then
...
fi

which probably looks more self explanatory, but here [ is actually a symbolic link to the test command itself. clever little trick basically.

...wow...

i did not know that the [ was just a link for test...

i had always used the if [...]; fi format with no idea it was the same as if test...

acid_kewpie · 02-25-2009, 03:11 PM

odd isn't it? And you'll find (afair) that you also must match it with ] at the end of the test binary whines for no logical reason, just neatness!

jlinkels · 02-25-2009, 08:29 PM

Believe it or not, Bash even has a formal language description. That is something I never had expected from something which seems so unlogical as bash to humans.

jlinkels