Linux Oneliners

• URL encode a string

perl -pe 'chomp ; s/(.)/sprintf(\"%%%02X\", ord($1))/seg;'

e.g. echo "hello" | perl -pe 'chomp ; s/(.)/sprintf("%%%02X", ord($1))/seg;'
will give: %68%65%6C%6C%6F

• URL decode a string

perl  -pe 's/\%([A-Fa-f0-9]{2})/pack('C', hex($1))/seg;'

e.g. echo "%68%65%6C%6C%6F" | perl  -pe 's/\%([A-Fa-f0-9]{2})/pack('C', hex($1))/seg;'
will give: hello

• base64 encode a string

perl -MMIME::Base64 -ne "print encode_base64($_)"

e.g.
echo "hallo een twee" | perl -MMIME::Base64 -ne 'print encode_base64($_)'
will give: aGFsbG8gZWVuIHR3ZWUK

• base64 decode a string

perl -MMIME::Base64 -ne "print decode_base64($_)"

e.g.
echo "aGFsbG8gZWVuIHR3ZWU" | perl -MMIME::Base64 -ne 'print decode_base64($_)'
will give: hallo een twee

• Make a screendump and save to a unique file name

xwd | convert - `date "+%Y%m%d:%H%M"`.jpg

Actually, you can also use the import command, both convert and import come from the indispensable ImageMagick tools. The syntax for import would be:

import `date "+%Y%m%d:%H%M"`.jpg

e.g. if you execute the command you get a crosshair cursor,
click on the window you want the screenshot of, and this will
produce a file something like: 20060821:1820.jpg

• list every perl module that is outdated

perl -MCPAN -e 'CPAN::Shell->r;'

e.g.
# perl -MCPAN -e 'CPAN::Shell->r;'
CPAN: Storable loaded ok
Going to read /root/.cpan/Metadata
  Database was generated on Mon, 21 Aug 2006 11:32:38 GMT

Package namespace         installed    latest  in CPAN file
Apache::SOAP                  undef      0.60  BYRNE/SOAP/SOAP-Lite-0.60a.tar.gz
Archive::Tar                   1.28      1.30  KANE/Archive-Tar-1.30.tar.gz
Archive::Zip                   1.12      1.16  SMPETERS/Archive-Zip-1.16.tar.gz
etc....

• update every perl module that is outdated on my disk:

perl -MCPAN -e 'CPAN::Shell->install(CPAN::Shell->r)'

• convert a unix timestamp in a file to human readable format

perl -pe 's/(\d{5,20})/localtime$1/eg' < filename

e.g.
# echo "1197206684 logging of some action" | perl -pe 's/(\d{5,20})/localtime$1/eg'
Sun Dec  9 14:24:44 2007 logging of some action

What's the UNIX timestamp? Have a look at:
www.unixtimestamp.com

• check an SSL enabled site from the commandline

openssl s_client -connect hostname:443

This will show you the certificate chain (the CA and the X.509 cert of the site itself) and also which cyphers are user in the connection. Use :443 for an https:// website and :993 for an imaps connection, and so on.

e.g.
[ ~]> openssl s_client -connect webmail.xs4all.nl:443
CONNECTED(00000003)
depth=0 /C=NL/O=*.xs4all.nl/OU=https://services.choicepoint.net/get.jsp?GT59386789/OU=See www.rapidssl.com/cps (c)05/OU=Domain Control Validated - RapidSSL(TM)/CN=*.xs4all.nl
...
New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA
Server public key is 1024 bit
SSL-Session:
    Protocol  : TLSv1
    Cipher    : DHE-RSA-AES256-SHA
etc...

• get an overview of which programs are listening on the network

netstat -tupan

This will show you whether it's an UDP or TCP service, the portnumber it's listening on and the Proccess ID plus Program name.


e.g.
[~]# netstat -tupan
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name
tcp        0      0 0.0.0.0:800                 0.0.0.0:*                   LISTEN      23517/rpc.mountd
tcp        0      0 0.0.0.0:2049                0.0.0.0:*                   LISTEN      -
tcp        0      0 0.0.0.0:111                 0.0.0.0:*                   LISTEN      1964/portmap
tcp        0      0 0.0.0.0:784                 0.0.0.0:*                   LISTEN      23500/rpc.rquotad
tcp        0      0 127.0.0.1:50000             0.0.0.0:*                   LISTEN      2208/hpiod
udp        0      0 0.0.0.0:781                 0.0.0.0:*                               23500/rpc.rquotad
udp        0      0 0.0.0.0:797                 0.0.0.0:*                               23517/rpc.mountd
udp        0      0 0.0.0.0:68                  0.0.0.0:*                               1901/dhclient
udp        0      0 0.0.0.0:111                 0.0.0.0:*                               1964/portmap
etc...

Use netstat -tupa to get service names instead of numbers
You can also use lsof -i
N.B.Even if a daemon is listening on a port number, connections from the outside might be blocked off by iptables firewalling.
check with iptables -nL
• Extract one file from an RPM package

rpm2cpio package.rpm |cpio -ivd path_without_leading_slash/filename

e.g.
[~]# rpm2cpio logrotate-1.0-1.i386.rpm |cpio -ivd usr/man/man8/logrotate.8
usr/man/man8/logrotate.8
14 blocks
[~]#

If you want to extract all files, just end with cpio -ivd and leave out the filename.
If you only want to look what's in the package, use rpm -qlp ;-)
or:

rpm2cpio package.rpm | cpio -tv

• Search and Replace a string on all files in a directory

perl -p -i -e 's/oldstring/newstring/g' *

You can also do this recursively on all files in the directory and the subdirectories beneath it with:


perl -p -i -e 's/oldstring/newstring/g' `find ./ -name *.html`

• Wake a machine through a wake-on-LAN packet

perl -MNet::Wake -e 'Net::Wake::by_udp(undef,"00:13:72:15:b8:87" ) '

Of course you need the perl Module Net::Wake installed. If you don't have it, install it from CPAN with:


perl -MCPAN -e 'install Net::Wake'

• print a file without configuring the printer

netcat 192.168.10.10 9100 < file.ps

Netcat connects to the printer (in this example with ip-address 192.168.10.10) on port 9100 and then just forwards the postscript file over that connection.
This trick should work with most HP Jetdirect printers.
• save a (video) stream to disk

mplayer -dumpstream -dumpfile whatever.rm rtsp://url-to-stream

You can have a look with another instance of mplayer while the first one is still downloading:

mplayer whatever.rm

An easy utility to find out de stream URL's (they are often hidden inside a lot of HTML and javascript) is:
streamsniff
just run streamsniff as root while connecting with your browser to the video stream.

dd if=/dev/hda1 | gzip -c | split -b 2000m - /somewhere/backup.img.gz.

cat /somewhere/backup.img.gz.* | gzip -dc | dd of=/dev/hda1

/usr/lib/sendmail -L sm-msp-queue -Ac -v -q