spinning-waiting-stick.sh

spinning-waiting-stick

#!/usr/bin/env bash
#
# Provides two different methods that can be used to display a spinning stick that will
# continue to spin until a specific process is finished running.
#
# NOTE: 'method_two' is notiblely faster than 'method_one'. Despite this, it does not
#       speak for the method's actual speed. That is dependent on how you use and
#       implement the methods. For the case of the examples that I provided, 'method_one'
#       is slower because I have it check if the incremented number is greater than or
#       equal to the specified stopping number, for every iteration of the for loop.
#       Though this might be obvious, checking during every iteration is not efficient
#       and should not be implemented in an actual program, unelss you have a good
#       reason. The only reason that I have 'method_one' do this, is because it allows
#       me to provide a simple example of situations in which either method could be
#       used.
#
########################################################################################
#### [ Variables ]


## Change the color of the output text.
green="$(printf '\033[0;32m')"
blue="$(printf '\033[0;34m')"
nc="$(printf '\033[0m')"
clrln="$(printf '\r\033[K')"


#### End of [ Variables ]
########################################################################################
#### [ Functions ]
#### Below are the two different methods (that I personally use) that can be used to
#### display a spinning stick.

########################################################################################
#### [[ method_one ]]
#### Using 'method_one' is ideal in all situations, with an exception of one. In a
#### situation where a variable is modified with the intent to be used later in the
#### code, 'method_two' is much more ideal. The reason for this is because when a
#### variable is modified orcreated inside of a subprocess/subshell, the changes to that
#### variable will be lost once the subprocess exits. For more information, refer to the
#### following link: https://github.com/koalaman/shellcheck/wiki/SC2031


method_one() {
    # Variable to be incremented.
    local var=0
    # The integer to stop itterating at.
    local stop_at=1000000

    ####
    # Function Info: Until a specified process is finished running, a spinning stick
    #                will output to the terminal, in place.
    #
    # Parameters:
    #   $1 - required
    #       Process ID of some command/function.
    ####
    waiting() {
        local spin="-\|/"
        local i=0

        ## If the process $1 exists, continuously output a new character inside of $spin
        ## to create the illusion of a spinning stick.
        while ps -p "$1" &>/dev/null; do
            i=$(( (i+1) %4 ))
            # NOTE: Here is a labeled version, describing how the below variable
            #       expansion works: '${parameter:offset:length} -> ${spin:$i:1}'
            #       You can find more information at the following link:
            #       https://mywiki.wooledge.org/BashGuide/Parameters#Parameter_Expansion
            printf "%sPerforming action: %s" "$clrln" "${spin:$i:1}"
            sleep .1
        done
    }

    ## Recursively store the new value of $i, into $var.
    ## NOTE: This for statement is executed as a background process.
    ## NOTE 2: This for statement represents the actions to be performed and waited
    ##         upon.
    for ((i = 0; i < (stop_at + 1); i++)); do
        var="$i"

        ## Once $i is greater than or equal to the value of $stop_at, output the value
        ## of $var.
        if ((i >= stop_at)); then
            # Output the new value of $var.
            printf "%sOutput of 'var': %s\n" "$clrln" "${green}${var}${nc}"
        fi
    done &

    # Execute the 'waiting' method, passing along the Process ID of the for statement.
    waiting "$!"
    echo -e "${green}==>${nc} Done with 'method_one'\n"
}


### End of [[ method_one ]]
########################################################################################
#### [[ method_two ]]
#### As mentioned in the description of 'method_one', 'method_two' is ideal in
#### situations were a variable is being modified with the intent of being used later in
#### the code.


method_two() {
    # Variable to be incremented.
    local var=0

    ####
    # Function Info: Until a specified process is finished running, a spinning stick
    #                will output to the terminal, in place.
    ####
    waiting() {
        local spin="-\|/"
        local i=0

        ## While true, continuously output a new character inside of $spin to create the
        ## illusion of a spinning stick.
        while true; do
            i=$(( (i+1) %4 ))
            # NOTE: Here is a labeled version, describing how the below variable
            #       expansion works: '${parameter:offset:length} -> ${spin:$i:1}'
            #       You can find more information at the following link:
            #       https://mywiki.wooledge.org/BashGuide/Parameters#Parameter_Expansion
            printf "%sPerforming action: %s" "$clrln" "${spin:$i:1}"
            sleep .1
        done
    }

    # Execute the 'waiting' method as a background process.
    waiting &
    # Save the Process ID of the executed function ('waiting').
    local _PID=$!

    ## Recursively store the new value of $i, into $var.
    ## NOTE: This represents the actions to be performed and waited upon.
    for i in {1..1000000}; do
        var="$i"
    done

    # Once the for loop has finished, kill the process executing the 'waiting' method.
    kill -9 $_PID &>/dev/null
    # Output the new value of $var.
    printf "%sOutput of 'var': %s\n" "$clrln" "${green}${var}"
    echo -e "==>$nc Done with 'method_two'\n"
}


#### End of [[ method_two ]]
########################################################################################
#### [ Main ]
#### Below puts both methods/examples to use.


echo -e "$blue==>$nc Executing 'method_one'"
method_one

echo ""

echo -e "$blue==>$nc Executing 'method_two'"
method_two


#### End of [ Main ]
########################################################################################