set properties file value by key via bash shell

setprop.sh

#!/bin/bash

############################
#script function
############################
setProperty(){
  awk -v pat="^$1=" -v value="$1=$2" '{ if ($0 ~ pat) print value; else print $0; }' $3 > $3.tmp
  mv $3.tmp $3
}
############################
### usage: setProperty $key $value $filename
setProperty "store.folder"              "/opt/current/store"     "env.properties"

@iyerusad Thanks, also can you add a func for add new variable?

You can call "newvar=somevalue" >> file.txt to append new string to file. But no, not updating at this time.

cat << 'EOF' > /usr/local/bin/setProperty

#!/bin/bash
#version: 0.2
### usage: setProperty key value filename

if [ -z "$1" ]; then
  echo "No parameters provided, exiting..."
  exit 1
fi
if [ -z "$2" ]; then
  echo "Key provided, but no value, breaking"
  exit 1
fi
if [ -z "$3" ] && [ -z "$setPropertyFile" ]; then
  echo "No file provided or setPropertyFile is not set, exiting..."
  exit 1
fi

if [ "$setPropertyFile" ] && [ "$3" ]; then
    echo "setPropertyFile variable is set AND filename in comamnd! Use only or the other. Exiting..."
    exit 1
else
  if [ "$3" ] && [ ! -f "$3" ]; then
    echo "File in command NOT FOUND!"
    exit 1
  elif [ "$setPropertyFile" ] && [ ! -f "$setPropertyFile" ]; then
    echo "File in setPropertyFile variable NOT FOUND!"
    exit 1
  fi
fi

if [ "$setPropertyFile" ]; then
  file=$setPropertyFile
else
  file=$3
fi

is_already_exist=`cat $file | grep $1 | cut -d'=' -f2`
if [ "$is_already_exist" ]; then
  awk -v pat="^$1=" -v value="$1=$2" '{ if ($0 ~ pat) print value; else print $0; }' "$file" > "$file".tmp
else
  cat $file > "$file".tmp
  echo "$1=$2" >> "$file".tmp
fi
mv "$file".tmp "$file"

EOF

chmod +x /usr/local/bin/setProperty

I've modified your script to reflect the requirements mentioned above
@iyerusad @Kolyall

Can you explain about the scripts with details