Commands by ynedelchev (4)

  • If you want to create fast a very big file for testing purposes and you do not care about its content, then you can use this command to create a file of arbitrary size within less than a second. Content of file will be all zero bytes. The trick is that the content is just not written to the disk, instead the space for it is somehow reserved on operating system level and file system level. It would be filled when first accessed/written (not sure about the mechanism that lies below, but it makes the file creation super fast). Instead of '1G' as in the example, you could use other modifiers like 200K for kilobytes (1024 bytes), 500M for megabytes (1024 * 1024 bytes), 20G for Gigabytes (1024*1024*1024 bytes), 30T for Terabytes (1024^4 bytes). Also P for Penta, etc... Command tested under Linux. Show Sample Output

    truncate --size 1G bigfile.txt
    ynedelchev · 2015-02-26 11:56:27 0
  • If you have a client that connects to a server via plain text protocol such as HTTP or FTP, with this command you can monitor the messages that the client sends to the server. Application level text stream will be dumped on the command line as well as saved in a file called proxy.txt. You have to change 8080 to the local port where you want your client to connect to. Change also to the IP address of the destination server and 80 to the port of the destination server. Then simply point your client to localhost 8080 (or whatever you changed it to). The traffic will be redirected to host on port 80 (or whatever you changed them to). Any requests from the client to the server will be dumped on the console as well as in the file "proxy.txt". Unfortunately the responses from the server will not be dumped. Show Sample Output

    mkfifo fifo; while true ; do echo "Waiting for new event"; nc -l 8080 < fifo | tee -a proxy.txt /dev/stderr | nc 80 > fifo ; done
    ynedelchev · 2015-01-14 09:26:54 2
  • This command will execute 1000 requests to the http URL handlink 100 concurent connections at a time. Then it will display statistics about the time that have been taken. Show Sample Output

    ab -n 1000 -c 100
    ynedelchev · 2014-02-18 09:32:01 0
  • This command will traverse all of the folders and subfolders under current working directory. For every file inside it, it will do a search inside the content of the file for a specific term 'what'. Then it will print a list of the lines that contain that term (and match that pattern). Each matching line will be preceded with the path and name to the file and then the line number iside taht file wehre the pattern was found. Then the actual content of the matching lien will be printed. The output will be piped throug less, so that the user can scroll through it if it goes beyond the limits of the current display window. Show Sample Output

    find . -exec grep -Hn what \{\} \; | less
    ynedelchev · 2014-02-17 09:59:01 0

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Import SQL into MySQL with a progress meter
This uses PV to monitor the progress of the MySQL import and displays it though Zenity. You could also do this pv ~/database.sql | mysql -u root -pPASSWORD -D database_name and get a display in the CLI that looks like this 2.19MB 0:00:06 [ 160kB/s] [> ] 5% ETA 0:01:40 My Nautalus script using this command is here

Selecting a random file/folder of a folder
I used only shuf command.

Find duplicate UID in /etc/passwd
You can use only awk

Combine all .mpeg files in current directory into one big one.
Good old cat & output redirection. Using this method you can combine all kinds of things - even mpeg files. My video camera makes a series of .mpeg files that are broken into 4gb chunks. Using this command I can easily join them together. Even better, combined with the cp command the files can be copied and joined in one step.

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seq can produce the same thing as Perl's ... operator.
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list block devices
Shows all block devices in a tree with descruptions of what they are.

Find common lines between two files

list and sort files by size in reverse order (file size in human readable output)
This command list and sort files by size and in reverse order, the reverse order is very helpful when you have a very long list and wish to have the biggest files at the bottom so you don't have scrool up. The file size info is in human readable output, so ex. 1K..234M...3G Tested with Linux (Red Hat Enterprise Edition)

bash or tcsh redirect both to stdout and to a file
When plumbers use pipes, they sometimes need a T-joint. The Unix equivalent to this is 'tee'. The -a flag tells 'tee' to append to the file, rather than clobbering it. Tested on bash and tcsh.

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