Horray... Its time to some shell script tips. In this article I'm going to use the "/bin/bash" interpreter, that is present in the vast majority of Linux installations, and even Unix or MacOS.

Let's see some isolated tips and at the end we'll put them together.

PID of your own Process

There are some variables that bash already give to us, like these:

• $$ ↣ The PID of the running process
• $PPID ↣ The Parent PID of the running process

#!/bin/bash
echo "My PID is " $$
echo "My Parent PID is " $PPID

Create a temp file

Use the "mktemp" command to create a temp file. Remember to remove it at the end of the execution of your shell script.

#!/bin/bash

# Create a temp file
FILE=`mktemp`
echo $FILE

# Dont forget to remove the file
rm -f $FILE

UpperCase or LowerCase

An easy way to transform your variable in UpperCase or LowerCase. Its not necessary any complex command with "awk", "sed", "regex", or other, just the built-in power of bash.

#!/bin/bash
VALUE="This Monday is very Hot"

echo "In Uppercase: ${VALUE^^}"
echo "In Lowercase: ${VALUE,,}"

Ask the user for some input

Lets use the "read" command to accomplish this.

#!/bin/bash
read -p "Do you want to continue? [Y/n]" A
if [ ! "${A}" == "Y" ]; then
  echo "Stopping now"
  exit 1
fi
exit 0

Echo with Colors? Yes, we can!

#!/bin/bash
# COLORS
red='\e[1;31m'
green='\e[1;32m'
yellow='\e[1;33m'
blue='\e[1;34m'
magenta='\e[1;35m'
cyan='\e[1;36m'
# NoColor
NC='\e[0m\033[0m'

echo_color() {
  echo -n -e "${1} ${NC}\n"
}

# Indicate the color that you want here
echo_color "${red}ERROR"
echo_color "${yellow}WARNING"
echo_color "${green}OK"

Script... Assemble!

#!/bin/bash
# Declare some colors
RED='\e[1;31m'
GREEN='\e[1;32m'
YELLOW='\e[1;33m'
BLUE='\e[1;34m'
MAGENTA='\e[1;35m'
CYAN='\e[1;36m'
# NoColor
NC='\e[0m\033[0m'

# Define the echo with color function
echo_color() {
  echo -n -e "${1} ${NC}\n"

}

# Use this function to exit your script
# It centralizes the exit and removes the temp file
close() {
  rm -f $FILE
  exit $1
}

FILE=`mktemp`

# Lets save our PID in the temp FILE
echo "$$" > $FILE

read -p "Do you want to print the value in the $FILE? [Y/n]" A
if [[ "${A}" == "Y" || "${A}" == "" ]]; then
	echo_color "${MAGENTA}`cat $FILE`"
else
	echo_color "${YELLOW}Not showing own PID value"
fi

read -p "Do you want to save the Parent PID? [yes/no]" A
if [ "${A,,}" == "yes" ]; then
	echo "$PPID" > $FILE
	echo_color "${RED}`cat $FILE`"
else
	echo_color "${YELLOW}Not showing Parent PID value"
fi

close 0