dev.chom.pl

There's one less-than-expected thing about TCP: even if you provide a small buffer to recv() and the other side sends exactly the same amount of data in the send() call, there's no guarantee that the data is received in one call.

Take for example Python:

# sock is a socket.socket(), already connected data = socket.recv(4) length = struct.unpack('=l', data)[0] # this might fail!

There are two ways to mitigate it:

really portable way: receive in a loop, until all data are received -- but beware of recv() returning b'' - this means there's an error in the communication

Python's fnmatch library makes it easy to convert human-readable glob pattern to re.match()-compatible regexps:

Python splits string via str.split() and str.rsplit() as well, the latter of which starts splitting from the end of the string. This can be useful when using the second parameter, maxsplit.

For example:

>>> "string with multiple spaces".split(" ", maxsplit=1) ['string', 'with multiple spaces']

NetworkManager usually puts "127.0.1.1" in /etc/resolv.conf. To get currently used DNS servers, type:

To summarise syscalls by time or count, use strace -c. To include child processed, add -f switch. For example:

To quickly in-/decrement number under cursor in Vim, use (in Normal):

to increment: Ctrl-A

When running a for-loop in zsh, you can skip do-done part, leaving only command, for example:

% for day in Mon Tue Wed Thu; date -d "next $day" Mon Apr 25 00:00:00 CEST 2016 Tue Apr 26 00:00:00 CEST 2016 Wed Apr 27 00:00:00 CEST 2016 Thu Apr 28 00:00:00 CEST 2016

In Normal mode, use ~ to switch case of letter under cursor. Similar commands are:

gU – to switch to upper-case

gu – to switch to lower-case

You can list mountpoints by file system type using mount -tTYPE. Example:

For those Debian-inclined, this may be surprising. You can install RPMs by providing an URL to either yum or rpm -i:

When logging on multiple machines with synchronized ~/.bashrc / ~/.zshrc you probably don't want to set PS1 on each machine separately. Solution based on hostname will be handy.

To derive user@hostname (or any other host-identifying command) into uniformly-distributed colours, use:

_host_colour=$(echo $(whoami)@$(hostname -f) | sum | awk "{print \$1 % 256 }")

GNU tool sum generates simple, short checksum which are then shortened down to 256 (the default Xterm colour count). Now add the variable to your PS1:

# Bash export PS1="\[\033[38;5;\${_host_colour}m\]\u@\h\[\033[0m\] % " # Zsh (requires module colors) export PS1="%F{\${_host_colour}}%n@%m%f %% "

Bash traps override rather than stack. Example:

You can use regular expressions in aptitude search. Example:

^node$

You can use variable names without $ in bash:

a=3 echo $(( a - 1 ))