Backticks

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November 23rd, 2012, 08:29 AM

ttremain

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Backticks

I have a command I need to run from a script, that requires backticks, but I'm not sure how to do that if I need to use backticks around the command itself too.

So I need to run this mysql query (which REQUIRES the backticks around the word Database):

Code:

show databases WHERE `Database` LIKE "central\_%"

Code:

for database in `mysql -Bse 'show databases WHERE `Database` LIKE "central\_%" OR `Database` LIKE "facebook\_%"`
do
  Something
done

Backticks within backticks don't work too well...

Any suggestions?

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Thomas Tremain

November 23rd, 2012, 10:57 AM

salem

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> So I need to run this mysql query (which REQUIRES the backticks around the word Database):
But backticks are shell magic.

If your shell is bash, then this seems like it should work.

Code:

for database in $(mysql -Bse 'show databases WHERE $(Database) LIKE "central\_%" OR $(Database) LIKE "facebook\_%")
do
  Something
done

But $(Database) gets evaluated twice, which might be a waste of effort.

So perhaps

Code:

mydb=$(Database)
for database in $(mysql -Bse 'show databases WHERE $mydb LIKE "central\_%" OR $mydb LIKE "facebook\_%")
do
  Something
done

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November 23rd, 2012, 12:13 PM

ttremain

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I appreciate your efforts there, but that does not meet the requirements.

The backticks around the word Database are NOT to be evaluated by bash, but need to be passed intact as part of the mysql query.

November 24th, 2012, 12:18 AM

salem

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I see.

Would something like this work?

Code:

function doit {
    mysql -Bse 'show databases WHERE `Database` LIKE "central\_%" OR `Database` LIKE "facebook\_%"'
}

for database in `doit` ; do 
    echo $database
done

Comments on this post

ttremain agrees: Thanks!

November 24th, 2012, 01:13 AM

ttremain

Contributing User

Join Date: Dec 2005

Location: Vancouver, WA, USA

Posts: 364

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Yes, that does work...

So does this workaround:

Code:

for database in `mysql -Bse 'show databases'`
do
  if [[ $database =~ ^(facebook|central)\_ ]]
  then
    do something 
  fi
done

The workaround doesn't solve the requirements, but does change them.

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