Commands by acavagni (11)

  • 0
    date | md5sum | sed -r 's/(..){3}/\1:/g;s/\s+-$//'
    acavagni · 2019-07-13 10:39:21 0
  • This is a slightly modified version of the knoppix5 user oneliner ( Show Sample Output

    seq -s '*' 40 | tr -dc '[*\n]'
    acavagni · 2019-07-01 07:24:47 0

  • 0
    eval "unset $(printenv | grep -ioP '(?:https?|no)_proxy' | tr '\n' ' ')"
    acavagni · 2019-06-28 10:40:41 0
  • I use it after a clean CentOS 7 minimal server installation to automatically populate the /etc/hosts file. Not sure why the installation does not add this entry by itself. Tested on CentOS 7 with the simplest use case: 1 static ip address and the hostname provided during installation. Show Sample Output

    echo "$(ip addr show dev $(ip r | grep -oP 'default.*dev \K\S*') | grep -oP '(?<=inet )[^/]*(?=/)') $(hostname -f) $(hostname -s)"
    acavagni · 2019-06-15 16:40:38 1
  • The vaule is expressed in megabytes Show Sample Output

    echo $[ ($(dpkg-query -s $(dpkg --get-selections | grep -oP '^.*(?=\binstall)') | grep -oP '(?<=Installed-Size: )\d+' | tr '\n' '+' | sed 's/+$//')) / 1024 ]
    acavagni · 2019-06-02 16:35:34 1
  • I put this command on my ~/.bashrc in order to learn something new about installed packages on my Debian/Ubuntu system each time I open a new terminal Show Sample Output

    dpkg-query --status $(dpkg --get-selections | awk '{print NR,$1}' | grep -oP "^$( echo $[ ( ${RANDOM} % $(dpkg --get-selections| wc -l) + 1 ) ] ) \K.*")
    acavagni · 2019-06-01 13:24:07 0
  • It uses the following GNU grep options: "-o" which shows only the matching part of the line and "-P" which allows the use of Perl regular expressions. Show Sample Output

    ip a | grep -oP '(?<=inet |addr:)(?:\d+\.){3}\d+'
    acavagni · 2019-03-21 20:53:06 0
  • This command could seem pretty pointless especially when you can get the same result more easily using the rpm builtin queryformat, like: rpm -qa --qf "%{NAME} %{VERSION} %{RELEASE}.%{ARCH}\n" | sort | column -t but nonetheless I've learned that sometimes it can be quite interesting trying to explore alternative ways to accomplish the same task (as Perl folks like to say: There's more than one way to do it!) Show Sample Output

    rpm -qa | sed 's/^\(.*\)-\([^-]\{1,\}\)-\([^-]\{1,\}\)$/\1 \2 \3/' | sort | column -t
    acavagni · 2019-03-14 21:11:45 0
  • It can be used to pinpoint the path(s) where the largest number of files resides when running out of free i-nodes Show Sample Output

    find / -type f ! -regex '^/\(dev\|proc\|run\|sys\).*' | sed 's@^\(.*\)/[^/]*$@\1@' | sort | uniq -c | sort -n | tail -n 10
    acavagni · 2019-03-06 20:36:14 0
  • useful for discarding even those comments which start with blanks or those empty lines which contain blanks Show Sample Output

    grep -vE '^\s*(#|$)' textfile
    acavagni · 2019-03-05 21:40:02 0
  • Useful to see at glance which directory under the root file is using most space Show Sample Output

    find / -maxdepth 1 -type d | xargs -I {} sh -c "mountpoint -q {} || du -sk {}" | sort -n
    acavagni · 2019-03-04 11:59:10 0

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Find default gateway

Remove duplicate entries in a file without sorting.
Using awk, find duplicates in a file without sorting, which reorders the contents. awk will not reorder them, and still find and remove duplicates which you can then redirect into another file.

Rename file to same name plus datestamp of last modification.
Note that the -i will not help in a script. Proper error checking is required.

search ubuntu packages to find which package contains the executable program programname
search ubuntu's remote package source repositories for a specific program to see which package contains it

listen to ram

Silently ensures that a FS is mounted on the given mount point (checks if it's OK, otherwise unmount, create dir and mount)
In my example, the mount point is /media/mpdr1 and the FS is /dev/sdd1 /mountpoint-path = /media/mpdr1 filesystem=/dev/sdd1 Why this command ? Well, in fact, with some external devices I used to face some issues : during data transfer from the device to the internal drive, some errors occurred and the device was unmounted and remounted again in a different folder. In such situations, the command mountpoint gave a positive result even if the FS wasn't properly mounted, that's why I added the df part. And if the device is not properly mounted, the command tries to unmount, to create the folder (if it exists already it will also work) and finally mount the FS on the given mount point.

Detect illegal access to kernel space, potentially useful for Meltdown detection
Based on capsule8 agent examples, not rigorously tested

Alias TAIL for automatic smart output
Run the alias command, then issue $ps aux | tail and resize your terminal window (putty/console/hyperterm/xterm/etc) then issue the same command and you'll understand. $ ${LINES:-`tput lines 2>/dev/null||echo -n 12`} Insructs the shell that if LINES is not set or null to use the output from `tput lines` ( ncurses based terminal access ) to get the number of lines in your terminal. But furthermore, in case that doesn't work either, it will default to using the default of 80. The default for TAIL is to output the last 10 lines, this alias changes the default to output the last x lines instead, where x is the number of lines currently displayed on your terminal - 7. The -7 is there so that the top line displayed is the command you ran that used TAIL, ie the prompt. Depending on whether your PS1 and/or PROMPT_COMMAND output more than 1 line (mine is 3) you will want to increase from -2. So with my prompt being the following, I need -7, or - 5 if I only want to display the commandline at the top. ( ) 275MB/748MB [7995:7993 - 0:186] 06:26:49 Thu Apr 08 [askapache@n1-backbone5:/dev/pts/0 +1] ~ $ In most shells the LINES variable is created automatically at login and updated when the terminal is resized (28 linux, 23/20 others for SIGWINCH) to contain the number of vertical lines that can fit in your terminal window. Because the alias doesn't hard-code the current LINES but relys on the $LINES variable, this is a dynamic alias that will always work on a tty device.

Running a command at a specific time

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

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