Getting permission denied error while executing shell command from ruby console. And the same shell command is working from shell.
From Shell..
tests@tests-workstation:~$ "`grep '^datadir=' /etc/mysql/my.cnf | cut -f 2 -d '='`/db_backups"
bash: /db_backups: is a directory
tests@tests-workstation:~$
From ruby console..
>> %x["`grep '^datadir=' /etc/mysql/my.cnf | cut -f 2 -d '='`/db_backups"]
sh: /db_backups: Permission denied
=> ""
Any Idea !
You're trying to execute a directory and the shells are saying no; bash says no by saying "/db_backups: is a directory" whereas sh says "/db_backups: Permission denied". If you just execute the backedticked part:
grep '^datadir=' /etc/mysql/my.cnf | cut -f 2 -d '='
You'll almost certainly see no output at all and the reason is probably that your regular expression is too tight, something like this:
grep '^[ ]*datadir[ ]*=' /etc/mysql/my.cnf | cut -f2 -d'='
Would serve you better; the character classes contain a space and a tab.
Now that you're looking for the right things we can move on to why it still won't work. The %x[] quoter tries to execute its argument using the shell. When you feed the backticked grep stuff:
`grep '^[ ]*datadir[ ]*=' /etc/mysql/my.cnf | cut -f2 -d'='`/db_backups
to the shell, you should get a directory name that ends with /db_backups but you can't execute a directory. I think you want this to produce the directory name:
d = %x[echo `grep '^[ ]*datadir[ ]*=' /etc/mysql/my.cnf | cut -f2 -d'='`/db_backups].strip
Note the leading echo and the .strip call on the returned string. The .strip is necessary to remove the newline from what echo produces.
I think you're going through a lot of trouble for something that could easily be done with just a couple lines of Ruby:
dir = nil
File.open('/etc/mysql/my.cnf').each do |line|
if(m = line.match(/^\s*datadir\s*=\s*(\S+)/))
dir = m[1] + '/db_backups'
break
end
end
You could probably tighten that up a bit if you wanted but I think that that's at least less confusing than putting shell backticks inside Ruby backticks.
It looks like you just want to get field 2 from the file. Then just do it in Ruby using split
File.open("file").each do |line|
if line[/^datadir/]
print line.split("=",2)[0]
end
end
There is no need to specifically shell out to call grep. This is inefficient and non-portable
bash: /db_backups: is a directorysure smells like an error message. What are you trying to accomplish? Why is the entire command in quotes?