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Scripting with Pharo

17 May 2015

A couple of links to set the scene, one from 2004, the other from 2005. Their titles relate to this post, although their content doesn't really.

While Pharo is an immersive interactive programming environment, it can also be used for operating system command line-oriented scripting. Take a freshly downloaded standard Pharo 4 image, here renamed p4cli.image:

% pharo -vm-display-null p4cli.image --list
Currently installed Command Line Handlers:
Fuel            Loads fuel files
config          Install and inspect Metacello Configurations from the command line
save            Rename the image and changes file
update          Load updates
printVersion    Print image version
st              Loads and executes .st source files
test            A command line test runner
clean           Run image cleanup
eval            Directly evaluates passed in one line scripts

Let's see how to use NBSQLite3's online backup functionality to back up a live SQLite database through a Pharo script.

Firstly, install the current bleedingEdge version of NBSQLite3.

% pharo -vm-display-null p4cli.image config \
      http://www.smalltalkhub.com/mc/Pharo/MetaRepoForPharo40/main \
      ConfigurationOfNBSQLite3 --install=bleedingEdge
'Installing ConfigurationOfNBSQLite3 bleedingEdge'

Loading 1.2 of ConfigurationOfNBSQLite3...
Fetched -> NBSQLite3-Core-PierceNg.7 --- ...
...finished 1.2%

Now make a script of the backup code snippet seen in my previous blog post, changing the database file names. In this case, I am using the script to make a copy of my server's firewall log database, which is live and constantly updated by the logging daemon. The script is named 'sqlitebackup.st'.

| srcDB dstDB backup |
srcDB := NBSQLite3Connection openOn: '/var/log/ulog/ulogd.db'.
dstDB := NBSQLite3Connection openOn: '/tmp/ulogd-backup.db'.
[   backup := NBSQLite3Backup new.
    srcDB asBackupSource: backup.
    dstDB asBackupDestination: backup.
    backup prepare.
    [ [ backup completed ] whileFalse: [ backup step ] ] ensure: [ backup finish ]
] ensure: [ srcDB close. dstDB close. ]

Run the script under Unix "time":

% time pharo -vm-display-null p4cli.image st --quit sqlitebackup.st
pharo -vm-display-null p4cli.image st --quit sqlitebackup.st 
0.26s user 0.10s system 53% cpu 0.675 total

% ls -l /var/log/ulog/ulogd.db* /tmp/*.db
-rw-r--r-- 1 pierce pierce 11636736 May 17 20:49 /tmp/ulogd-backup.db
-rw-r--r-- 1 ulog   ulog   11643904 May 17 20:50 /var/log/ulog/ulogd.db

The database files aren't identical, because the logging daemon has written yet more data since the backup was taken.

Tags: scripting, SQLite