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COMMON SHELL COMMANDS cat [filename] | Display file’s contents to the standard output device (usually your monitor). |
cd /directorypath | Change to directory. |
chmod [options] mode filename | Change a file’s permissions. |
chown [options] filename | Change who owns a file. |
clear | Clear a command line screen/window for a fresh start. |
cp [options] source destination | Copy files and directories. |
date [options] | Display or set the system date and time. |
df [options] | Display used and available disk space. |
du [options] | Show how much space each file takes up. |
file [options] filename | Determine what type of data is within a file. |
find [pathname] [expression] | Search for files matching a provided pattern. |
grep [options] pattern [filesname] | Search files or output for a particular pattern. |
kill [options] pid | Stop a process. If the process refuses to stop, use kill -9 pid. |
less [options] [filename] | View the contents of a file one page at a time. |
ln [options] source [destination] | Create a shortcut. |
locate filename | Search a copy of your filesystem for the specified filename. |
lpr [options] | Send a print job. |
ls [options] | List directory contents. |
man [command] | Display the help information for the specified command. |
mkdir [options] directory | Create a new directory. |
mv [options] source destination | Rename or move file(s) or directories. |
passwd [name [password]] | Change the password or allow (for the system administrator) to change any password. |
ps [options] | Display a snapshot of the currently running processes. |
pwd | Display the pathname for the current directory. |
rm [options] directory | Remove (delete) file(s) and/or directories. |
rmdir [options] directory | Delete empty directories. |
ssh [options] user@machine | Remotely log in to another Linux machine, over the network. Leave an ssh session by typing exit. |
su [options] [user [arguments]] | Switch to another user account. |
tail [options] [filename] | Display the last n lines of a file (the default is 10). |
tar [options] filename | Store and extract files from a tarfile (.tar) or tarball (.tar.gz or .tgz). |
top | Displays the resources being used on your system. Press q to exit. |
touch filename | Create an empty file with the specified name. |
who [options] | Display who is logged on. http://www.caffeinecodes.com |
x ? y : z --> [z, y][bool(x)]
x
is already a boolean type (or an integer of value 0 or 1), you can omit the bool()
function, of course.)y
does not contain a boolean False equivalent:x ? y : z --> bool(x) and y or z
import sys
if not hasattr(sys, "hexversion") or sys.hexversion < 0x020300f0:
sys.stderr.write("Sorry, your Python is too old.\n")
sys.stderr.write("Please upgrade at least to 2.3.\n")
sys.exit(1)
import
statements. The variable hexversion
is only available since Python 1.5.2, so we first check if it is there, just in case someone has an even older version. The format of the variable is 0x
<maj><min><rev><rel> (major, minor and revision number, and an indication of the release status, which is f0
for official final releases). Each of the four parts is two hexadecimal digits.cgitb
" module (available since Python 2.2) is extremely helpful when debugging CGI programs. Whenever a run-time error (i.e. exception) occurs, a nicely formatted HTML fragment will be produced, containing the backtrace with source context, line numbers and even contents of the variables involved. To use this module, put this line somewhere at the top of your CGI program:import cgitb; cgitb.enable()
data = zip(list1, list2)
data.sort()
list1, list2 = map(lambda t: list(t), zip(*data))
tuple1, tuple2 = zip(*data)
mac = ":".join([i.zfill(2) for i in mac.split(":")]).lower()
zfill
method of string objects is available since Python 2.2.2.)for i in range(len(ips)):
ips[i] = "%3s.%3s.%3s.%3s" % tuple(ips[i].split("."))
ips.sort()
for i in range(len(ips)):
ips[i] = ips[i].replace(" ", "")
getopt
module) in a sophisticated way. In this example, the program accepts three options (both as one-letter options and as long options) and requires at least two arguments.import sys, getopt, os.path
me = os.path.basename(sys.argv[0])
debug = False
really = True
verbose = False
my_options = (
("d", "debug", "debug = True", "Enable debug mode."),
("n", "notreally", "really = False", "No action, display only."),
("v", "verbose", "verbose = True", "Increase verbosity.")
)
short_opts = reduce(lambda a, b: a + b[0], my_options, "")
long_opts = map(lambda x: x[1], my_options)
def usage ():
args = "[-%s] <dir1> <dir2> [...]" % short_opts
print >> sys.stderr, "Usage: ", me, args, "\nOptions:"
for opt in my_options:
print >> sys.stderr, "-" + opt[0], opt[3]
sys.exit(1)
try:
opts, args = getopt.getopt(sys.argv[1:], short_opts, long_opts)
except getopt.GetoptError:
usage()
for o, p in opts:
for shrt, lng, action in my_options:
if o[1:] in shrt or o[2:] == lng:
exec action
break
else:
usage()
if len(args) < 2:
usage()
#!/bin/sh
line). The embedded shell commands check if Python is installed. If not, a useful error message is displayed and the script exits. Otherwise, if Python is found, the script is re-executed with it. Python ignores the triple-quoted doc string and executes the rest like a normal Python program.#!/bin/sh
"""":
if which python >/dev/null; then
exec python "$0" "$@"
else
echo "${0##*/}: Python not found. Please install Python." >&2
exit 1
fi
"""
__doc__ = """
Demonstrate how to mix Python + shell script.
"""
import sys
print "Hello World!"
print "This is Python", sys.version
print "This is my argument vector:", sys.argv
print "This is my doc string:", __doc__
sys.exit (0)
import signal
def signal_numtoname (num):
name = []
for key in signal.__dict__.keys():
if key.startswith("SIG") and getattr(signal, key) == num:
name.append (key)
if len(name) == 1:
return name[0]
else:
return str(num)
rvm
on an Ubuntu 14.04 VPS, and use it to install a stable version of Ruby and Rails. Although you can go through these procedures as the root user, we'll assume you're operating using an unprivileged user as shown in steps 1-4 in this guide.rvm
is to run the following commands as a regular user:gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
\curl -sSL https://get.rvm.io | bash -s stable --rails
gpg
command contacts a public key server and requests a key associated with the given ID. In this case we are requesting the RVM project's key which is used to sign each RVM release. Having the RVM project's public key allows us to verify the legitimacy of the RVM release we will be downloading, which is signed with the matching private key.\curl
portion uses the curl
web grabbing utility to grab a script file from the rvm
website. The backslash that leads the command ensures that we are using the regular curl
command and not any altered, aliased version.-s
flag indicates that the utility should operate in silent mode, the -S
flag overrides some of this to allow curl
to output errors if it fails. The -L
flag tells the utility to follow redirects.bash
for processing. The -s
flag indicates that the input is coming from standard in. We then specify that we want the latest stable version of rvm
, and that we also want to install the latest stable Rails version, which will pull in the associated Ruby.rvm
scripts by typing:source ~/.rvm/scripts/rvm
rvm
like this:rvm install ruby_version
rvm list
rvm use ruby_version
gemsets
and then installing Rails within those using the normal gem
commands:rvm gemset create gemset_name # create a gemset rvm ruby_version@gemset_name # specify Ruby version and our new gemset gem install rails -v rails_version # install specific Rails version