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Linux basic basch script if-then-else statement


If-then-else statement is quite a helpful statement and definitely helps to make life easier in scripting and other programming languages.

In basch script, the syntax is quite easy to follow and of course the logic is always the same even in other programming languages.

Logic can be followed literally as it is written.

Bash script below assumes that there 4 USB hard drive and is labelled as “USB Week1 Backup”, 
“USB Week2 Backup”, “USB Week3 Backup” and “USB Week4 Backup”.

If  the USB inserted and is mounted on “/media” the script gets the USB name and assigns it to variable name “PathBackup”

In Bash script the if statement is enclosed with open and close brackets, then spaces in between the brackets should be followed or else the script will result to an error.

if [ -d "$W1" ] – this statement checks if the ”-d” directory $W1  is present and assigns the path "/media/USB Week1 Backup" to PathBackup.

Spaces between the if statement , in open and close statement brackets should be followed.

In getting the value assigned to a variable use the dollar sign like “$W1”, in this case theW1 has the string value of ="/media/USB Week1 Backup".

  elif  - is else if (should be written in small letters)

  fi – to end or finish the if-then-else statement

rsync  -av /home/mybackup_data | gzip > "$PathBackup"`date '+%m-%d-%Y'`.zip

Statement above copies the files or data from /home/mybackup_data, and zip the files and filename is the date that it was copied.

Bash script below can be used as a backup utility use it on crontab to automate the backup.
-------------------------------------------------------------- 
   #!/bin/sh
  
   W1="/media/USB Week1 Backup"
   W2="/media/USB Week2 Backup"
   W3="/media/USB Week3 Backup"
   W4="/media/USB Week4 Backup"

         if [ -d "$W1" ]
                 then
                     PathBackup="$W1"

            elif [ -d "$W2" ]
                then
                     PathBackup="$W2"

            elif [ -d "$W3" ]
                 then
                     PathBackup="$W3"

            elif [ -d "$W4" ]
                 then
                      PathBackup="$W4"

          fi



rsync  -av /home/mybackup_data | gzip > "$PathBackup"`date '+%m-%d-%Y'`.zip

#-------------------------------------------------------------- 

As your mileage vary through the years of course, things will get exciting always. But if you are just beginning to grasp the world of bash scripting then start the basic right and understand it thoroughly, then the next will be easy.

Cheers! Hope it helps...Enjoy scripting..

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