Bash “Rotating” MySQL backup

I'm quite a novice in shell scripting so far, but i'm learning and getting quite comfortable in writing shell scripts, but i have a lot to learn.

The snippet at the bottom of the page creates backups of a certain users databases.

The script checks first if there is more than 7 compressed .gz files in a folder.

Fetches oldest gz archive and removes it.

Checks for latest .sql backup and compresses it with gzip

Creates a new .sql dump

The script is run once a day

How would you write this differently?

#!/bin/bash

BACKUPPATH=/var/mysql_backup/
mkdir -p $BACKUPPATH
if [ $(ls -l $BACKUPPATH*.gz 2>/dev/null | wc -l) -gt 7 ]; then
        OLD=$(find $BACKUPPATH -type f -name '*.gz' -printf '%T+ %p\n' | sort | head -n 1 | awk '{print $2}')
        rm $OLD # Removing oldest compressed archive
fi

if [ $(ls -l $BACKUPPATH*.sql 2>/dev/null | wc -l) -eq 1 ]; then
        LATESTLOG=$(find $BACKUPPATH -type f -name '*.sql' -printf '%p\n' | head -n 1)
        gzip $LATESTLOG
fi

/usr/bin/mysqldump -u db_user -p'password' --single-transaction  --all-databases > $BACKUPPATH$(date "+%Y.%m.%d-%H.%M.%S")_dump.sql

I'd do this:

#!/bin/bash

backuppath=/var/mysql_backup
mkdir -p "$backuppath"

shopt -s nullglob

# Remove old compressed archive
backups=( "$backuppath"/*.gz )
if [[ ${#backups[@]} -gt 0 ]]; then
stat -c "%Y %n" "${backups[@]}" |
sort -rn |
sed -e '1,7d' -e 's/^[0-9]\+ //' |
xargs -r rm
fi

# Compress all the logs
logs=( "$backuppath"/*.sql )
if [[ ${#logs[@]} -gt 0 ]]; then
gzip "${logs[@]}"
fi

/usr/bin/mysqldump -u db_user -p'password' --single-transaction --all-databases \
> "$backuppath/"$(date "+%Y.%m.%d-%H.%M.%S")_dump.sql


Notes:

• don't use ALLCAPSVARS -- leave those for the shell. I've seen people accidentally do PATH=... and then wonder why their script is broken.

• don't parse ls -- I'm using arrays to hold the results of the glob expansion, and checking how many elements are in the array.

• always quote variables, except when you know exactly why not. See https://unix.stackexchange.com/q/171346/4667

• I'm assuming you want to compress any log.sql file, not just the first found

• I'm assuming you want to keep 7 compressed logs and remove any older ones.

• I'm assuming you have the GNU coreutils (xargs -r, those stat options)

StackExchange Code Review Q#119118, answer score: 8