Jul 192014
Jul 192014
After last night’s photo posting, another couple from Southsea/Old Portsmouth :-
The Railings
The Railings
The Empty Seat
The Empty Seat
Jul 182014
No, I’m not not intending to get rid of the Leica. It’s just that I’d recently been using an old 4Gbyte SD card (which turned out to be somewhat flaky and required more effort than usual to extract from), and run out of power – resulting in the camera thinking it was 1970! So the following are not dated correctly, but that isn’t the most interesting part of a photo :-
1943
1943
Just goes to show that the council may not get around to clearing up rubbish for a while!
The Kiss
The Kiss
The Race
The Race
Three Boats
Three Boats
Too many boats!
Jul 042014
Well, relatively safely anyway.
The other day I felt the urge to knock up some SQL to clean up a MySQL table I’m responsible for. So I got the SQL prepared, but then needed to find out how to run this as a cron job (or batch file if you prefer). This was because I wanted to run the job on a regular and frequent basis; and I’m too lazy to sit around with a stopwatch running the same command every 15 minute.
I came up with a method that I knew wasn’t recommended – as it said so in the manual. The method involved passing the contents of a file to the command line (i.e. mysql -u root -p$(cat somefile). And today I decided to have a look around to see if there was a better way.
It turns out that much of the most visible advice on the Internet is wrong. It all suggests using the -p option where the account password is visible in the process table (i.e. you can read it with ps aux). If you can guarantee that no rogue person will be able to login to your server and read the process table, then you are safe; and I would like to ask how you can achieve the impossible.
Putting a password in a file (as suggested below) is at least somewhat better, but it would be nice if MySQL were to offer something a bit more sophisticated.
However, on to the method.
The first step is to create an options file, and make sure that it is readable only by the current user :-
$ touch mysql-options-root.cnf $ chmod go= mysql-options-root.cnf
Once securely created, you can edit the file and add the relevant options :-
[client] password=do-you-really-think-i-would-tell-the-internet-what-my-mysql-root-password-is?
That list of options is fairly minimal; it only specifies the password to use. You can add additional options – just use the normal command-line options without the hyphens.
To use this options file, add the command-line option –defaults-extra-file=${filename}. A full example follows :-
$ mysql --defaults-extra-file=mysql-options-root.cnf --user=root --host=polio <use misc; heredoc> select count(*) from films; heredoc> END
The output is not included (it’s none of your business how many films I’ve watched). And yes this does work for what I intended it to.
As has been pointed out, it is also possible to schedule batch jobs within MySQL itself which may be a better answer in most cases.
Jul 032014
It is nice to make a shell environment more pleasant to use in many ways, but it is also helpful to ensure that the process degrades gracefully …
For example, I have a section in my .zshrc which creates an ls alias to use human-readable values, and to colourise the output :-
ls --color=auto > /dev/null 2>&1 # Just collect the exit status ... if [ "$?" = 0 ] then # If there is no error then use the --color option alias ls='ls -h --color=auto' else alias ls='ls -h' fi
Thus when logging into a system that has an ls command that lacks the –color option, the alias will not create an ls command that immediately fails. Now whilst such systems are getting rather more rare than in the past, this graceful degradation is still useful as a principle. Whether creating shell aliases, or more generally.
As another example, I have a shell alias (page or also pg) that I use to invoke a “pager” like more, less, pg, or my preferred choice, most. The relevant section within the zshrc file is :-
for candidate in more less most
do
p=$(which $candidate)
if [ "$?" = "0" ]
then
alias pg=$candidate
alias page=$candidate
PAGER=$candidate
fi
done
This repeatedly sets up the two aliases (and sets the PAGER environment variable) if the candidate pager is available; otherwise the aliases are left alone. In other words, this works through a list of candidates in order from most available to least available (but preferred) to select one. Once used to using page as a command, I no longer need to worry about if most is installed on a system.
A very similar loop is used to generate an alias called vim which will always work (at least when vi is available).