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Old 01-01-2017, 05:14 AM   #1
ShadyThGod
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Is it possible to create a custom command line inside a BASH script?


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.
 
Old 01-01-2017, 06:16 AM   #2
wpeckham
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Quote:
Originally Posted by ShadyThGod View Post
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.
 
Old 01-01-2017, 06:49 AM   #3
nodir
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Registered: May 2016
Posts: 222

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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
 
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Old 01-01-2017, 09:43 AM   #4
ondoho
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Quote:
Originally Posted by ShadyThGod View Post
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.
 
Old 01-01-2017, 11:01 AM   #5
wpeckham
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Quote:
Originally Posted by ondoho View Post
...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!
 
Old 01-03-2017, 04:49 AM   #6
ondoho
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Quote:
Originally Posted by wpeckham View Post
Code:
if ( "$command" == "help" ) then
bash chokes on the missing ';' (or newline) before 'then'...
 
Old 01-03-2017, 05:39 AM   #7
wpeckham
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Registered: Apr 2010
Location: Continental USA
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Quote:
Originally Posted by ondoho View Post
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. ;-)
 
  


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