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Thread: How to insert a variable into a complex CLI command using Bash script?

  1. #1
    Join Date
    May 2020
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    Distro
    Ubuntu 20.04 Focal Fossa

    How to insert a variable into a complex CLI command using Bash script?

    Hi Ubuntu users,

    I'm a newbie when it comes to Bash/Shell-scripting. So I have tried to simplify the issue where I'm stuck at with this uname -a example script. What I'm trying to do is to insert a variable containing the flag -a into the command uname with Bash scripting.

    The reason for dumbing it down like this, is because I have a much more complex and longer Nmap command containing a mix of double and single quotes, which I'm working on but can't understand and make it work. I will have to create a separate thread for that Nmap command if I get that far with my understanding.

    I also used this Shell-script analysis tool, to the best of my abilities which somebody at StackOverflow mentioned. I read a couple of those threads and various Bash tutorials on the Internet. But I couldn't understand how to proceed with this problem.
    https://www.shellcheck.net/


    concat_3.sh
    PHP Code:
    #!/usr/bin/bash

    endpoint=' -a'

    # myvar=`whoami`
    # myvar=$(uname -a)
    # myvar=$(uname "$1")
    myvar=$(uname $1)

    # Example 1
    echo ""
    echo "=== Example 1 ==="
    script_1="Argument 1 is: $myvar"
    echo "$script_1"
    echo ""

    # Example 2
    echo "=== Example 2 ==="
    script_2="Argument 1 is: $1"
    echo "$script_2" "$myvar"
    echo ""

    # Print $myvar and $endpoint
    echo '=== Print $myvar and $endpoint ==='
    echo "$myvar" "$endpoint"
    echo ""

    # Example 3
    endpoint3=' -a'

    echo "=== Example 3 ==="
    script_3="uname $1"
    echo "$script_3" "$endpoint3"
    echo "" 
    output
    Code:
    $ bash concat_3.sh
    
    === Example 1 ===
    Argument 1 is: Linux
    
    === Example 2 ===
    Argument 1 is:  Linux
    
    === Print $myvar and $endpoint ===
    Linux  -a
    
    === Example 3 ===
    uname   -a

  2. #2
    Join Date
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    Re: How to insert a variable into a complex CLI command using Bash script?

    Try:

    Code:
    echo $( uname -a )
    Google for "ABSG bash" to get to the advanced bash scripting guide. If you don't already know how to program, there's a "beginners bash scripting guide", but the advanced one has all the beginning stuff, intermediate stuff AND the advanced stuff, so I usually just use it.

    If you want to pass in arguments from the command line, there are many ways to accomplish that. If there's more than 1 possible argument, using the getopts built-in bash function is probably best. For just 1 argument and a script that only you will use, you can hard-code something like this:
    Code:
    #!/bin/bash
    
    SEARCH="$1"
    if [ "$SEARCH" == "-u" ] ; then  
       # do some things for that option
    fi
    
    # do other stuff whether the option was provided or not.
    This is the bash method to run external programs:
    $( call other commands with options here )

    The safest way to reference variables is to use "${variable_name}", including the quotes. It is common to build a path to a file ... using different parts.
    Code:
    total_filename="${TOP_DIR}/etc/config"
    With that, we can use ${total_filename} to refer to where ever it points elsewhere in the script.

  3. #3
    Join Date
    May 2020
    Location
    Earthrealm
    Beans
    27
    Distro
    Ubuntu 20.04 Focal Fossa

    Re: How to insert a variable into a complex CLI command using Bash script?

    Thanks for the ABSG (Adv. Bash-Scripting Guide), I'll be back!
    https://tldp.org/LDP/abs/html/

    Misc.
    https://tldp.org/guides.html
    https://tldp.org/LDP/Bash-Beginners-...tml/index.html

    Thanks!
    Last edited by mortalkorona; August 27th, 2023 at 09:33 AM.

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