BASH issue, counting variables in an array for FOR loop

Question

I'm having an issue with the following script. Due to my lack of knowledge of BASH, I am not 100% sure how to create a loop that uses "for" to count the amount of variables in an array and loop through each of them. Basically what I am wanting to do is having the script count up the amount of variables in variable $sqldumps, then run a MySQL Dump for each of them (also logging them into a database). The long version of the script is posted at the bottom, but here is a short version below:

#! /usr/bin/env bash
echo -ne '\033]0;World of Clucky - Backup\007'
BINDIR="$(dirname "$(readlink -fn "$0")")"
cd "$BINDIR"
sqldumps=("lwc" "bans" "frisnuk_permissions" "jail" "imonies" "GriefP" "permissions" "showcase" "simpleclans")
#Copy MySQL Databases
echo "[`date '+%H:%M'`] Starting MySQL Backup" >> /home/clucky/MinecraftServers/backup.log
for i in ${#sqldumps[*]}
    do
        echo "     ${sqldumps[i]}" >> /home/clucky/MinecraftServers/backup.log;
        /opt/lampp/bin/mysqldump -u'root' -p'CENSORED' --skip-lock-tables ${sqldumps[i]} > /home/clucky/MinecraftServers/.backups/$timedate/MySQL/${sqldumps[i]}.sql;
    done
echo "     forum";
/opt/lampp/bin/mysqldump -u'root' -p'CENSORED' forum >> /home/clucky/MinecraftServers/.backups/$timedate/MySQL/forum.sql;
echo "[`date '+%H:%M'`] MySQL Backup Complete" >> /home/clucky/MinecraftServers/backup.log

The line in particular that I am having issues with is:

for i in ${#sqldumps[*]}

I am assuming that I am using the wrong syntax for this, so if anyone could give me the correct one, it would be greatly appreciated. Thank you!

#! /usr/bin/env bash
echo -ne '\033]0;World of Clucky - Backup\007'
BINDIR="$(dirname "$(readlink -fn "$0")")"
cd "$BINDIR"
timedate=`date '+%m.%d.%Y-%H:%M'`
sqldumps=("lwc" "bans" "frisnuk_permissions" "jail" "imonies" "GriefP" "permissions" "showcase" "simpleclans")
echo "-------------- `date '+%d-%B-%Y %H:%M'` --------------" >> /home/clucky/MinecraftServers/backup.log
echo "[`date '+%H:%M'`] Starting Minecraft Backup" >> /home/clucky/MinecraftServers/backup.log
mkdir -p /home/clucky/MinecraftServers/.backups/$timedate
mkdir -p /home/clucky/MinecraftServers/.backups/$timedate/MySQL
nice --adjustment=19 tar -zcpf /home/clucky/MinecraftServers/.backups/$timedate/Minecraft.tar.gz \
    --directory /home/clucky/MinecraftServers/ \
    --exclude=SkyBlockkit \
    --exclude=Tekkit \
    --exclude=Vanilla \
    --exclude=test \
    --exclude=Zflocco_LP \
    --exclude=Mortuus/plugins/dynmap/web --exclude=Mortuus/plugins/AutoSaveWorld/backups --exclude Mortuus/CraftBukkitVersion --exclude=Mortuus/orebfuscator_cache --exclude=Mortuus/plugins/#Removed --exclude=Mortuus/server.log \
    --exclude=Frisnuk/plugins/dynmap/web --exclude=Frisnuk/plugins/AutoSaveWorld/backups --exclude Frisnuk/CraftBukkitVersion --exclude=Frisnuk/orebfuscator_cache --exclude=Frisnuk/plugins/#Removed --exclude=Frisnuk/plugins/#AwaitingUpdate --exclude=Frisnuk/server.log --exclude=Frisnuk/Suwako_Moriya100 --exclude=Frisnuk/Uk_Shadow --exclude=Frisnuk/Whiteghost99 --exclude=Frisnuk/greenrangermatt \
    --exclude=dailybackup.log \
    --exclude=.backups \
    --exclude=backup.log \
    --exclude=backups.log \
    --exclude=backupscript.sh \
    --exclude=dailybackup.sh \
    --exclude=.keptbackups .
echo "[`date '+%H:%M'`] Minecraft Backup Complete" >> /home/clucky/MinecraftServers/backup.log
#Purge files 3 days old
echo "[`date '+%H:%M'`] Purging Old Backups" >> /home/clucky/MinecraftServers/backup.log
find /home/clucky/MinecraftServers/.backups* -mmin +4320 -exec rm --recursive {} \;
echo "[`date '+%H:%M'`] Purging Complete" >> /home/clucky/MinecraftServers/backup.log
#Copy MySQL Databases
echo "[`date '+%H:%M'`] Starting MySQL Backup" >> /home/clucky/MinecraftServers/backup.log
for i in ${#sqldumps[*]}
    do
        echo "     ${sqldumps[i]}" >> /home/clucky/MinecraftServers/backup.log;
        /opt/lampp/bin/mysqldump -u'root' -p'CENSORED' --skip-lock-tables ${sqldumps[i]} > /home/clucky/MinecraftServers/.backups/$timedate/MySQL/${sqldumps[i]}.sql;
    done
echo "     forum";
/opt/lampp/bin/mysqldump -u'root' -p'CENSORED' forum >> /home/clucky/MinecraftServers/.backups/$timedate/MySQL/forum.sql;
echo "[`date '+%H:%M'`] MySQL Backup Complete" >> /home/clucky/MinecraftServers/backup.log
echo "[`date '+%H:%M'`] Daily Backup Complete" >> /home/clucky/MinecraftServers/backup.log
#Read back file size
filesize=$(ls -lah /home/clucky/MinecraftServers/.backups/$timedate | awk '{ print $5}')
echo "     Total Compression Size: $filesize\n" >> /home/clucky/MinecraftServers/backup.log

Thank you for your assistance!

Do you need to know the number of variables in the array or could you just use the array "map" method? — Four_lo
– Four_lo, Commented Mar 13, 2013 at 23:16
Truely, i really dont know. I just need a way for the script to loop through all of the variables in the array $sqldumps and run a MySQL dump for each. — Clucky
– Clucky, Commented Mar 13, 2013 at 23:25

danfuzz · Accepted Answer · 2013-03-14 00:07:02Z

2

The syntax ${#varname[*]} returns the size of the array, but the for syntax you use wants to be given a list of elements. So, either you want:

for elem in "${varname[@]}"; do
    ... something with ${elem} ...
done

or

for (( i = 0; i < ${#varname[@]}; i++ )); do
    ... something with ${varname[$i]} ...
done

Note, I use @ instead of * as that's generally a good prophylactic against elements that contain spaces (even though it may not strictly be necessary in this case).

edited Mar 14, 2013 at 0:07

answered Mar 13, 2013 at 23:24

danfuzz

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1 Comment

Clucky Over a year ago

WORKED GREAT! THANKS! I tried the second one, and it worked exactly as I needed it to. Also, thanks for the tip about the * and @ as I was wondering what the difference was. :)

William Pursell · Accepted Answer · 2013-03-13 23:24:03Z

2

Don't index over the array, just use the values:

for value in "${sqldumps[@]}"; do echo $value; done

answered Mar 13, 2013 at 23:24

William Pursell

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2 Comments

Clucky Over a year ago

I do need the variable i to increment by 1 each time though, right? so how would I specify this?

Gordon Davisson Over a year ago

@JesseAaronBellas: With this form, you don't need i at all. The only thing you needed it for was to fetch the i'th element of the array, and this form gives you the elements directly. Just replace ${sqldumps[i]} with $value inside the loop, and you're set.

John Kugelman · Accepted Answer · 2013-03-13 23:37:48Z

I've taken the liberty of reorganizing your script a bit to make it more readable.

#!/usr/bin/env bash

# Script starts here.
main() {
    backup_dir=~clucky/MinecraftServers
    dbs=(lwc bans frisnuk_permissions jail imonies GriefP permissions showcase simpleclans forum)

    echo -ne '\033]0;World of Clucky - Backup\007'

    log 'Starting MySQL Backup'
    dump_dbs "${dbs[@]}"
    log 'MySQL Backup Complete'
}

# Write a timestamped message to the log file.
log() {
    echo "[$(date '+%H:%M')] $*" >> "$backup_dir/backup.log"
}

# Dump each of the databases passed as an argument. The list of databases is "$@".
dump_dbs() {
    for db in "$@"; do
        # Use --skip-lock-tables for every database except "forum".
        local options=(--skip-lock-tables)
        [[ $db = forum ]] && options=()

        log "     $db"
        /opt/lampp/bin/mysqldump -u root -p CENSORED "${options[@]}" "$db" \
            > "$backup_dir/.backups/$timedate/MySQL/$db.sql"
    done
}

main "$@"

Here are some of the things I did:

Rather than iterating over the array indices, a loop like this will iterate over each value directly:
```
for value in "${array[@]}"; do ...; done
```
It's shorter to use ~user to refer to a user's home directory. It's also safer as users' home directories aren't necessarily under /home.
Breaking up the code into separate functions helps eliminate some of the redundancies such as writing the full path to backup.log repeatedly. The log() function puts the timestamped message line in one place.
The forum table doesn't get the --skip-lock-tables option so I made that more explicit which made it possible to get rid of the duplicate mysqldump line.
I removed quotes from places they weren't needed.

cinelli · Accepted Answer · 2013-03-13 23:44:39Z

0

$i will hold each item in an array incrementing itself until it reaches the end. So you don't have to reference the array each time you need it within the for loop. I also, don't like to hard code echo, this is a personal preference, so I swapped it out with printf.

for i in ${#sqldumps[@]}
  do
    printf "     %s" "$i" >> /home/clucky/MinecraftServers/backup.log;
    /opt/lampp/bin/mysqldump -u'root' -p'CENSORED' --skip-lock-tables $i > /home/clucky/MinecraftServers/.backups/$timedate/MySQL/${sqldumps[i]}.sql;
done

If you would just like to find the size of an array you could use.

Length=${#sqldumps[@]}

And $Length would then equal the number of places in the array

answered Mar 13, 2013 at 23:44

cinelli

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