Bash Script Linux - combines a QUIET function with other functions without hiding some of them

• Use #!/usr/bin/env bash instead of #!/bin/bash;
• Use only lowercase for your variable names;
• Do not mix echo and printf commands;
• Do not mix $... and %... in printf arguments;
• function fct_name () { ... } is older, use simply syntax fct_name () { ... }
• Do not declare variables in loops;
• To prevent errors in tests, redirect all outputs in trash with >/dev/null 2>&1 like this:

while my_cmd >/dev/null 2>&1; do
  ...do something...
done

• It's not necessary to put your command in [ ... ] or [[ ... ]] blocks to test condition or loop. The return code of command is used. Example:

while ps -p $the_pid >/dev/null 2>&1; do
  ...
done

• Like many commands (ls, find...), put a grep after ps is ugly and dangerous. Try to use command options often as possible
  • With ps command, use -p, --ppid options to filter on process and -o to reduce output to the minimum necessary;
• Use shellcheck tool on command line to improve your programs. If you use Visual Studio Code or VS Codium, install the ShellCheck extension;
• When you often move the cursor with ANSI sequence, hide the cursor. Of course, do not forget to restore the cursor visible;
• Don't forget to restore ANSI modes and cursor if keystoke [CTRL]+[C] signal is used on your program (see trap command).

So, my spinner program result based on your work:

#!/usr/bin/env bash

# ASCII characters

declare -r char_esc=$'\e'

# ANSI sequences

declare -r ansi_csi="${char_esc}["

declare -r normal_mode="${ansi_csi}0m"
declare -r fg_green="${ansi_csi}32m"
declare -r fg_red="${ansi_csi}31m"
declare -r fg_purple="${ansi_csi}35m"
declare -r fg_yellow="${ansi_csi}33m"
declare -r fg_cyan="${ansi_csi}36m"

declare -r cursor_visible="${ansi_csi}?25h"
declare -r cursor_unvisible="${ansi_csi}?25l"

declare -r cursor_save_position="${ansi_csi}s"
declare -r cursor_restore_position="${ansi_csi}u"

declare -r erase_line="${ansi_csi}2K"

# On exit, restore mode and cursor visibility
# Useful when you use [CTRL]+[C]
on_sigint () {
    printf "%s" "$normal_mode$cursor_visible"
    printf "\nBye!\n"
    exit 1
}
trap on_sigint SIGINT

# Run quietly
run_quietly () {
    "$@" > /dev/null 2>&1
}

# Check command status and print something
declare -r text_ok="${fg_green}✔${normal_mode}"
declare -r text_error="${fg_red}🞮${normal_mode}"
check_cmd () {
    local -i pid=$1
    if wait $pid; then
        printf "[%s]\n" "$text_ok"
    else
        printf "[%s]\n" "$text_error"
    fi
}

# Run a spinner on a process
run_spinner () {
    local -i pid=$1
    local delay=0.1
    local spinstr='⠖⠲⠴⠦'
    local text_size=50
    printf "%s" "$cursor_unvisible$cursor_save_position"
    # shellcheck disable=SC2155
    local text=$(ps --ppid $pid -o args= 2>/dev/null)
    # shellcheck disable=SC2181
    while [[ $? -eq 0 ]]; do
        printf "%s[%s] %-*.*s" "$cursor_restore_position$normal_mode" "$fg_yellow${spinstr:0:1}$normal_mode" "$text_size" "$text_size" "$text"
        spinstr="${spinstr#?}${spinstr:0:1}"
        sleep $delay
        text=$(ps --ppid $pid -o args= 2>/dev/null)
    done
    printf "%s" "$erase_line$cursor_restore_position$cursor_visible"
}

# Run a command quietly with a spinner
run_cmd_with_spinner () {
    local -i pid=0
    # Do not forget the "&"
    run_quietly "$@" &
    pid=$!
    run_spinner $pid
    check_cmd $pid
}

# My program
my_long_command () {
    sleep 5
    sleep 2
    sleep 1
    # return 0 # Just for test
    return 1 # Just for test
}

run_cmd_with_spinner my_long_command