Copy file, backing up the destination file if its different form the source.

copy-file.sh

#!/bin/bash
#!/bin/bash

function copy-file {
    SRC=$1
    DEST=$2

    # Make sure DEST is a file
    if  [ ! -f "$SRC" ]; then
        echo "Source file does not exist"
        return 1;
    fi

    # Make sure DEST is a file
    if [ -d "$DEST" ]; then
        $DEST="$DEST/$(basename $SRC)"
    else
        if [ ! -d "$(dirname "${DEST}")" ]; then
            echo "Dest folder does not exist"
            return 1;
        fi
    fi

    if [ ! -f "$DEST" ]; then
        cp $SRC $DEST
        return 0;
    fi

    STATUS="$(cmp -s $SRC $DEST; echo $?)"  # "$?" gives exit status for each comparison
    if [[ $STATUS -eq 0 ]]; then  # if status isn't equal to 0, then execute code
        return 0;
    fi

    BACKUP_BASE="$DEST.bak"
    BACKUP_FILE=$BACKUP_BASE
    BACKUP_NUM=1
    until [ ! -f $BACKUP_FILE ] ; do
        BACKUP_FILE=$BACKUP_BASE"."$BACKUP_NUM
        ((BACKUP_NUM=BACKUP_NUM+1))
    done

    mv $DEST $BACKUP_FILE
    cp $SRC $DEST
}

function copy-folder {
    SRC=$1
    DEST=$2

    ## https://unix.stackexchange.com/a/139381/332745
    while IFS= read -r -d '' -u 9
    do
        echo "copy-file $REPLY $DEST$REPLY"
    done 9< <( find $SRC -type f -exec printf '%s\0' {} + )
}