Is it possible to create a custom command line inside a BASH script?

ShadyThGod · 01-01-2017, 05:14 AM

I was wondering if it was possible to create a custom command-line in BASH script. I tried using the read command to take input and use IF/ELIF statements to compare the input and run functions according to them but I can only use real bash commands. For eg -
This is what i'm currently trying to work with:

Code:

read $command
if ( "$command" == "help" ) then
    echo "Welcome to the Help Page"
elif ( "$command" == "clear" ) then
    clear
elif ( "$command" == "exit" ) then
    exit
fi

The clear and exit work properly but help starts the bash help command instead of echo-ing what i asked.

wpeckham · 01-01-2017, 06:16 AM

Quote:

Originally Posted by ShadyThGod

I was wondering if it was possible to create a custom command-line in BASH script. I tried using the read command to take input and use IF/ELIF statements to compare the input and run functions according to them but I can only use real bash commands. For eg -
This is what i'm currently trying to work with:

Code:

read $command
if ( "$command" == "help" ) then
    echo "Welcome to the Help Page"
elif ( "$command" == "clear" ) then
    clear
elif ( "$command" == "exit" ) then
    exit
fi

The clear and exit work properly but help starts the bash help command instead of echo-ing what i asked.

Bash troubleshooting is an art, but not one difficult to learn.
I assume these lines are in a script. If they are not, put them in one.
1. Check the command

Code:

 set -x

or use the #! line with options -xv to bash. You will want to revert these after you fix your issues. The output of the script when using this option needs to be captured to a file for later examination. The output will contain the commands, parameters, and output all together: lending itself to proper analysis.
2. Using commands that are bash internal makes your scripts more prone to issues. There are more conditions where internals are detected and executed, though there are ways to avoid this. Just a thought.
3. You may want to read about the

Code:

case

statement. It should be well covered in the bash documentation.

Let us see if that much gets you started.

nodir · 01-01-2017, 06:49 AM

There are a couple of things not doing what you expect them to do.
Look here, third example
http://mywiki.wooledge.org/BashGuide..._and_.5B.5B.29

Round the lines of this should be good:

Code:

#!/bin/bash
read command

if [[ "$command" = "help" ]]; then
    echo "Welcome to the Help Page"
elif [[ "$command" = "clear" ]]; then
    clear
elif [[ "$command" = "exit" ]]; then
    exit
fi

ondoho · 01-01-2017, 09:43 AM

Quote:

Originally Posted by ShadyThGod

Code:

read $command
if ( "$command" == "help" ) then
    echo "Welcome to the Help Page"
elif ( "$command" == "clear" ) then
    clear
elif ( "$command" == "exit" ) then
    exit
fi

...in other words, this is not a bash script.

wpeckham · 01-01-2017, 11:01 AM

Quote:

Originally Posted by ondoho

...in other words, this is not a bash script.

In fact, if I remember correctly this line run in a bash script

Code:

if ( "$command" == "help" ) then

will execute the command

Code:

"$command" == "help"

in a subshell and return the exit code to if to determine what to do next. I strongly suspect that is not your intent.

I could be wrong, but I believe you need to spend a lot more time looking at the man pages and examples available using google!

ondoho · 01-03-2017, 04:49 AM

Quote:

Originally Posted by wpeckham

Code:

if ( "$command" == "help" ) then

bash chokes on the missing ';' (or newline) before 'then'...

wpeckham · 01-03-2017, 05:39 AM

Quote:

Originally Posted by ondoho

bash chokes on the missing ';' (or newline) before 'then'...

I liked your comment

Quote:

...in other words, this is not a bash script.

better. There is nothing wrong there except the syntax and the logic. ;-)