Computing

2023-01-25 Backup a file using Bash

I keep most of my stuff under source control, but sometimes I need to keep an actual backup of a file because of the circumstances in which it is created or used.

I have a bash script that I use for this which keeps a rolling 3 backup copies of the file, so each time it is run providing the file has changed it moves copy 2 to copy 3 and copy 1 to copy 2 copy and then copies the actual file to copy 1 etc.

#!/bin/bash

if [ -z "${1}" ]
    then echo "Please input something"
    exit 1
fi

fileExists(){
    if   [ -d "${1}" ]
        then echo "${1} is a directory"
        return 1
    elif [ -f "${1}" ]
        then return 0
    else echo "${1} is not valid"
        return 1
    fi
}

FILENAME=${1}

if fileExists ${FILENAME}
    then echo "Backing up file ${FILENAME}"
else echo cannot backup ${FILENAME}
    exit 1 
fi

echo Checking if file is same as existing backup
if [ -e "${FILENAME}" ]; then
    if [ -e "${FILENAME}-1" ]; then
        SHA1=`sha1sum ${FILENAME} | awk '{print $1;}'`
        SHA1BK1=`sha1sum ${FILENAME}-1 | awk '{print $1;}'`
        if [ "${SHA1}" = "${SHA1BK1}" ]; then
                echo "Nothing has changed ${SHA1} versus ${SHA1BK1}"
                exit 1
        fi
    fi
fi

# archive existing tars
if [ -e "${FILENAME}" ]; then
   for a in 2 1
   do
     let b="${a}+1"
     if [ -e "${FILENAME}-${b}" ]; then
        rm "${FILENAME}-${b}"
     fi
     if [ -e "${FILENAME}-${a}" ]; then
        mv "$FILENAME-${a}" "$FILENAME-${b}"
     fi
    done
    cp "${FILENAME}" "${FILENAME}-1"
fi


echo "backup completed"
exit 0

The script first checks (top of script) to see that a file name was specified on the input line.

Then we have defined a fileExists function that checks a file is a valid file.

It checks we have a valid file by calling the above fileExists function using the filename passed in when the script is run.

It then compares using a checksum to see if the file is different from current latest backup.

If it is different then it loops through moving previous copies to a later version and finally copying the file to the latest backup.