Commands by quintic (4)

  • Suppose you have 11 marbles, 4 of which are red, the rest being blue. The marbles are indistinguishable, apart from colour. How many different ways are there to arrange the marbles in a line? And how many ways are there to arrange them so that no two red marbles are adjacent? There are simple mathematical solutions to these questions, but it's also possible to generate and count all possibilities directly on the command line, using little more than brace expansion, grep and wc! The answer to the question posed above is that there are 330 ways of arranging the marbles in a line, 70 of which have no two red marbles adjacent. See the sample output. To follow the call to marbles 11 4: after c=''; for i in $(seq $1); do c+='{b,r}'; done;, $c equals {b,r}{b,r}{b,r}{b,r}{b,r}{b,r}{b,r}{b,r}{b,r}{b,r}{b,r} After x=$(eval echo $c), and brace expansion, $x equals bbbbbbbbbbb bbbbbbbbbbr ... rrrrrrrrrrb rrrrrrrrrrr, which is all 2^11 = 2048 strings of 11 b's and r's. After p=''; for i in $(seq $2); do p+='b*r'; done;, $p equals b*rb*rb*rb*r Next, after y=$(grep -wo "${p}b*" Finally, grep -vc 'rr' Show Sample Output

    marbles () { c=''; for i in $(seq $1); do c+='{b,r}'; done; x=$(eval echo $c); p=''; for i in $(seq $2); do p+='b*r'; done; y=$(grep -wo "${p}b*" <<< $x); wc -l <<< "$y"; grep -vc 'rr' <<< "$y"; }
    quintic · 2010-08-27 23:04:33 0
  • If the return code from the last command was greater than zero, colour part of your prompt red. The commands give a prompt like this: [user current_directory]$ After an error, the "[user" part is automatically coloured red. Tested using bash on xterm and terminal. Place in your .bashrc or .bash_profile.

    export PROMPT_COMMAND='if (($? > 0)); then echo -ne "\033[1;31m"; fi'; export PS1='[\[\]\u\[\033[0m\] \[\033[1;34m\]\w\[\033[0m\]]\$ '
    quintic · 2010-08-25 21:19:30 0
  • tail -c 1 "$1" returns the last byte in the file. Command substitution deletes any trailing newlines, so if the file ended in a newline $(tail -c 1 "$1") is now empty, and the -z test succeeds. However, $a will also be empty for an empty file, so we add -s "$1" to check that the file has a size greater than zero. Finally, -f "$1" checks that the file is a regular file -- not a directory or a socket, etc. Show Sample Output

    endnl () { [[ -f "$1" && -s "$1" && -z $(tail -c 1 "$1") ]]; }
    quintic · 2010-08-25 12:06:10 0

  • -3
    (cd /bin; set -- *; x=$((1+($RANDOM % $#))); man ${!x})
    quintic · 2010-08-20 17:19:56 0

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Password Generation
Produces secure passwords that satisfy most rules for secure passwords and can be customized for correct output as needed. See "man pwgen" for details.

List your largest installed packages.
Calculates the size on disk for each package installed on the filesystem (or removed but not purged). This is missing the $ | sort -rn which would put the biggest packges on top. That was purposely left out as the command is slightly on the slow side Also you may need to run this as root as some files can only be checked by du if you can read them ;)

Scroll up (or Down (PgDn)) in any terminal session (except KDE)

Show drive names next to their full serial number (and disk info)
As of this writing, this requires a fairly recent version of util-linux, but is much simpler than the previous alternatives. Basically, lsblk gives a nice, human readable interface to all the blkid stuff. (Of course, I wouldn't recommend this if you're going to be parsing the output.) This command takes all the fun out of the previous nifty pipelines, but I felt I ought to at least mention it as an alternative since it is the most practical.

Find all folder in /var that contains log in their path and have more than 10 files inside them, print the folder and the count
-L is for following symbolic links, it can be omitted and then you can find in your whole / dir

Batch Convert SVG to PNG (in parallel)
Convert some SVG files into PNG using ImageMagick's convert command. Run the conversions in parallel to save time. This is safer than robinro's forkbomb approach :-) xargs runs four processes at a time -P4

Convert CSV to JSON
Replace 'csv_file.csv' with your filename.

To find the uptime of each process-id of particular service or process

Get AWS temporary credentials ready to export based on a MFA virtual appliance
You might want to secure your AWS operations requiring to use a MFA token. But then to use API or tools, you need to pass credentials generated with a MFA token. This commands asks you for the MFA code and retrieves these credentials using AWS Cli. To print the exports, you can use: `awk '{ print "export AWS_ACCESS_KEY_ID=\"" $1 "\"\n" "export AWS_SECRET_ACCESS_KEY=\"" $2 "\"\n" "export AWS_SESSION_TOKEN=\"" $3 "\"" }'` You must adapt the command line to include: * $MFA_IDis ARN of the virtual MFA or serial number of the physical one * TTL for the credentials

Set laptop display brightness
Run as root. Path may vary depending on laptop model and video card (this was tested on an Acer laptop with ATI HD3200 video). $ cat /proc/acpi/video/VGA/LCD/brightness to discover the possible values for your display.

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