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Replace all ocurrences in the file.
The g option is to replace more than one occurrence in the same line. Whitout the g option, it only replace the first occurrence in the line.
This is a simple case of recursing through all directories, adding the '.bak' extension to every file. Of course, the 'cp $file $file.bak' could be any code you need to apply to your recursion, including tests, other functions, creating variables, doing math, etc. Simple and clean recursion.
Useful mainly for debugging or troubleshooting an application or system, such as X11, Apache, Bind, DHCP and others. Another useful switch that can be combined with -mmin, -mtime and so forth is -daystart. For example, to find files that were modified in the /etc directory only yesterday:
sudo find /etc -daystart -mtime 1 -type f
Redirect the local port 2000 to the remote port 3000. The same but UDP:
nc -u -l -p 2000 -c "nc -u example.org 3000"
It may be used to "convert" TCP client to UDP server (or viceversa):
nc -l -p 2000 -c "nc -u example.org 3000"
It allows customizing by means of lesspipe. You need to write a ~/.lessfilter script and put this into your ~/.bashrc:
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Saved my day, when my harddrive got stuck in read-only mode.
Traffic details on the Ethernet interface.
Search the pattern in bzip2 compressed file with out having to unzip.
Gives information about user's home directory and real name and shell user is having.
Get the hard disk information with out shutting down and opening the system.
It gives information on model no., serial no., cylinders/heads/sectors, and the supported features of the hard disk.
To know the OS distro and version, release.
Is same like /etc/redhat-release
This is useful if you have a program which doesn't work well with multicore CPUs. With taskset you can set its CPU affinity to run on only one core.
I use this command to save RTSP video streams over night from one of our national TV stations, so I won't have to squeeze the data through my slow internet connection when I want to watch it the next day.
For ease of use, you might want to put this in a file:
mplayer -dumpstream -dumpfile "$FILE" -playlist "$1"
allows simple C shell access to the power of bc - never could figure out how to do the same thing with Bash - that's why I use tcsh most of the time.
Compares two versions with dpkg. It is not always obvious what version dpkg/apt will consider to be more recent. Operators include the following :
* These treat an empty version as earlier than any version: lt le eq ne ge gt.
* These treat an empty version as later than any version: lt-nl le-nl ge-nl gt-nl.
* These are provided only for compatibility with control file syntax: < > >.
This command doesn't output anything. It only returns with status 0 or 1, hence the echo "y" || echo "n" to get an output.
This command kills all processes with 'SomeCommand' in the process name. There are other more elegant ways to extract the process names from ps but they are hard to remember and not portable across platforms. Use this command with caution as you could accidentally kill other matching processes!
xargs is particularly handy in this case because it makes it easy to feed the process IDs to kill and it also ensures that you don't try to feed too many PIDs to kill at once and overflow the command-line buffer.
Note that if you are attempting to kill many thousands of runaway processes at once you should use 'kill -9'. Otherwise the system will try to bring each process into memory before killing it and you could run out of memory. Typically when you want to kill many processes at once it is because you are already in a low memory situation so if you don't 'kill -9' you will make things worse