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1. List open connections of a process

   $ lsof -i -a -p 99340
   

1. Remove .DS_Store files

   Delete recursively starting from current directory.

   $ find . -name .DS_Store -ls -exec rm {} ;
   

   To be used through an alias such as rmDS, for instance.

   If you don't need to print the delete file names:

   $ find . -name ".DS_Store" -delete
   

2. Extract certificates from OS X applications

   $ codesign -dvvvv --extract-certificates /Applications/Mail.app
   

   The certificates are saved in DER format, named codesign0, codesign1, ...

   They can be displayed with OpenSSL :

   $ openssl x509 -inform DER -in codesign0 -text
   

1. Read a huge file line by line

   fileinput reads lines sequentially, but doesn't keep them in memory.

   import fileinput
   
   for line in fileinput.input(['path']):
       print line
   

1. Stop a process

   $ kill -STOP <PID>
   $ kill -CONT <PID>
   

2. Change a byte in a file with direct access

   Set the 4th byte of /tmp/test to 0xFF:

   $ printf '\xFF' | dd bs=1 seek=4 conv=notrunc of=/tmp/test
   

1. Build a dictionary with list comprehension

   >>> dict((k, []) for k in ['a', 'b', 'c'])
   {'a': [], 'c': [], 'b': []}
   

2. Parse NSDate descriptions

   from datetime import datetime
   from dateutil.parser import parse
   
   print parse("Tue, 22 Jul 2008 08:17:41 +0200")
   

   2008-07-22 08:17:41+02:00

   or

   from dateutil.parser import parse
   print parse("Tue, 22 Jul 2008 08:17:41 +0200")
   

   2008-07-22 08:17:41+02:00

3. OS X English Dictionary Lookup

   import DictionaryServices
   s = "love"
   print DictionaryServices.DCSCopyTextDefinition(None, s, (0,len(s)))
   

   love |lʌv| noun 1 a strong feeling of affection: ...

1. Thread safe dispatch once

   Thread safe code to be run only once with all other thread waiting at the barrier:

   static dispatch_once_t onceToken;
   
   dispatch_once (&onceToken, ^{
       // ...    
   });
   

1. Javascript interpreter

   $ /System/Library/Frameworks/JavaScriptCore.framework/Versions/Current/Resources/jsc
   > 1+1
   2
   

2. All the files you downloaded

   $ sqlite3 ~/Library/Preferences/com.apple.LaunchServices.QuarantineEventsV* 'select LSQuarantineDataURLString from LSQuarantineEvent'
   

   you can delete the table with:

   $ sqlite3 ~/Library/Preferences/com.apple.LaunchServices.QuarantineEventsV* 'delete from LSQuarantineEvent'
   

1. Code profiling

   Let the profiler execute the code

   import hotshot
   
   prof = hotshot.Profile("hotshot_stats.prof")
   prof.runcall(my_function)
   prof.close()
   

   Display results

   from hotshot import stats
   
   s = stats.load("hotshot_stats.prof")
   s.strip_dirs()
   s.sort_stats('time', 'calls')
   s.print_stats(20)
   

1. Inline assembly with Intel syntax

   // $ gcc -m32 -fasm-blocks asm.c -o asm
   
   #include <stdio.h>
   
   int main (int argc, char *argv[]) {
   
       int espValue;
   
       _asm {
             mov [espValue], esp;
       }
   
       printf("espValue: %u\n", espValue);
   
       return 0;
   }
   

1. Breaking on a stripped binary with no main function

   (gdb) inf files
   Symbols from "/private/tmp/hello".
   Mac OS X executable:
       /private/tmp/hello, file type mach-o-le.
       Entry point: 0x000000f4
       0x00000000 - 0x00000042 is LC_SEGMENT.__TEXT in /private/tmp/hello
       0x000000e8 - 0x00000128 is LC_SEGMENT.__TEXT.__text in /private/tmp/hello