command misinterpreted by bash

Question

I'm wring a script that I plan to schedule by cron for 1AM each morning to backup a mySql DB.

Normally I use this to dump the database:

mysqldump --no-create-db --single-transaction myDB | gzip > ~/my_backup.sql.gz

In my head what I have written should:

Dump the DB, Write any errors to database.err
Pipe the output to gzip which then zips it up and writes to disk
Read the return code, assuming success write the file to a S3 bucket
For the purposes of testing writes current state to the shell

#!/bin/bash

# This script will run each night to backup
# the mySql DB then will upload to Amazon S3

DB_NAME="myDB"

S3_BUCKET="my.s3.bucket"

BACKUP_PATH="~/backups/${DB_NAME}.sql.gz"

mysqldump --no-create-db --single-transaction ${DB_NAME} 2> database.err | gzip > ${BACKUP_PATH}
if [ "$?" -eq 0 ]
then
    echo "Database dump complted sucessuflly... wtiting to S3"
    aws s3 cp ${BACKUP_PATH} s3://${S3_BUCKET}/
    if [ "$?" -eq 0 ]
    then
        echo "Backup sucessfully written to S3"
    else
        echo "Error writing to S3"
    fi
else
    echo "Mysqldump encountered a problem look in database.err for information"
fi

What it looks like the script is doing is getting to the mysqldump line, but is unable to differentiate between the parameter where i specify the DB and the 2> (file descriptor I think is the term?). This is the error:

./backup-script: line 12: ~/backups/myDB.sql.gz: No such file or directory
mysqldump: Got error: 1049: Unknown database 'myDB 2' when selecting the database
Mysqldump encountered a problem look in database.err for information

Can anyone suggest what is happening here/what I'm doing wrong.

In other words, use BACKUP_PATH=~/"backups/${DB_NAME}.sql.gz" or, better yet, BACKUP_PATH="$HOME/backups/${DB_NAME}.sql.gz" — John1024
– John1024, Commented Aug 29, 2017 at 23:37
One possibility for the cause of Unknown database 'myDB 2' is the space between ${DB_NAME} and 2> being something other than a standard ASCII space. Problems of this type happen if one creates scripts in a word processor instead of a programmer's editor. This is more common that you might think. — John1024
– John1024, Commented Aug 29, 2017 at 23:40
I have got myself into a habit or re-typing code that doesn't work. I have found copying from stackoverflow in some cases puts a zero-length space on the clipboard, and copying from hipchat to PhpStorm has given me some issues before as well. I can't remember if I have done it in this instance but will give that a try see if it let me put the command in the order I normally do for the sake of consistencey. — Craig
– Craig, Commented Aug 29, 2017 at 23:47

Kamran · Accepted Answer · 2017-08-29 23:21:56Z

1

Try putting the database name first

mysqldump "${DB_NAME}" --no-create-db --single-transaction

answered Aug 29, 2017 at 23:21

Kamran

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1 Comment

Craig Over a year ago

Also thanks to Kevin and John1024 for explaining about ~ and suggesting $HOME. Now whit is working I have realised I have captured the exit code of gzip but found this stackoverflow.com/questions/1221833/… to help me out. Thanks all!

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