Tag Archives: unix

Split a file on any character in Python

I need to split a big text file on a certain character. I expect I am being thick about this, but [`split`][split] doesn’t quite do what I want because it includes the matching line, whereas I want to split right on the matching character.

My Python answer:

def readlines(filename, endings, chunksize=4096):
“””Returns a generator that splits on lines in a file with the given
line = ”
while True:
buf = filename.read(chunksize)
if not buf:
yield line

line = line + buf

while endings in line:
idx = line.index(endings) + len(endings)
yield line[:idx]
line = line[idx:]

if __name__ == “__main__”:
import sys, os

FORMFEED = chr(12) # ASCII 12
basename = os.path.basename(sys.argv[1])
for num, data in enumerate(readlines(open(sys.argv[1]), endings=FORMFEED)):
filename = basename + ‘-‘ + str(num)
open(filename, ‘wb’).write(data)

This is also useful when reading data exported from some old-fashioned Mac application like [Filemaker 5][filemaker] where the line-endings are ASCII 13 not ASCII 10.

This post was inspired by [Lotus Notes][lotus] version 8.5, which is so advanced that to save a message in a file on disk you have to export it as structured text. And if you want to save a whole bunch of messages as individual files you must forget that [drag-and-drop was introduced with System 7][mactech], that would be too obvious.

[filemaker]: http://www.filemaker.com/support/downloads/downloads_prev_versions.html
[split]: http://developer.apple.com/Mac/library/documentation/Darwin/Reference/ManPages/man1/split.1.html
[lotus]: http://www-01.ibm.com/software/lotus/products/notes/
[mactech]: http://www.mactech.com/articles/mactech/Vol.10/10.06/DragAndDrop/index.html

Removing printing restrictions in 10.5

I am trying to write a good one-liner for removing all restrictions on printing for Mac OS X 10.5. I had thought that [`sed`][sed] would be perfect for this, but I can’t arrive at a simple syntax for appending new lines that works well when pasted into a terminal window. Here’s what I ended up with:

perl -p -0 -i ‘.bak’ -e ‘s/(Policy default).*(Policy)/$1>\n\nOrder deny,allow\nAllow from all\n<\/Limit>\n<$2/s' /private/etc/cups/cupsd.conf Rather brutal, it just guts the default policy and replaces it with the following:

Order deny,allow
Allow from all

Greg Neagle has [a useful article about printing in the enterprise][mactech]. Apple suggests [adding the network group to the local lpadmin group][ht3511], but points out that mobile users would need to be added individually. In my case most accounts are mobile accounts and we trust everyone to manage print queues on a Mac, so removing all restrictions is acceptable.

[mactech]: http://www.mactech.com/articles/mactech/Vol.24/24.06/2406MacEnterprise-LeopardPrinting/index.html
[ht3511]: http://support.apple.com/kb/HT3511
[sed]: http://developer.apple.com/mac/library/documentation/Darwin/Reference/ManPages/man1/sed.1.html

Using screen to log a terminal session

Note to self: [use screen][1] when doing a bunch of remote administration stuff over an SSH connection. You can tell it to log the session to a separate file, and can detach the session and log off without having the remote shell be terminated. Then later you can resume the session and haven’t lost anything.

To start a shell and log everything to a file, do

screen -L -S mysession

That drops you into a new shell, and lets you refer to that session later (in case you are ambitious and have many screen sessions running simultaneously). To detach the session type `CTRL+a` then `d`. From there you can exit cleanly. To resume the session later, type

screen -r mysession

The session history will be saved to a file named `screenlog.0` or similar in the directory where screen was first invoked.

[screen man page online][2] (Hmmm… looks like the hmug man pages have renamed themselves.)

I should use `screen` more often. I should also get in the habit of going through the contents of $PATH every time Mac OS X gets updated.

[1]: http://www.gnu.org/software/screen/
[2]: http://www.manpagez.com/man/1/screen/