Commands by alperyilmaz (22)

  • Limit memory usage per script/program

    When I'm testing some scripts or programs, they end up using more memory than anticipated. In that case, computer nearly halts due to swap space usage, and sometimes I have to press Magic SysRq+REISUB to reboot. So, I was looking for a way to limit memory usage per script and found out that ulimit can limit memory. If you run it this way: $ ulimit -v 1000000 . $ scriptname Then the new memory limit will be valid for that shell. I think changing the limit within a subshell is much more flexible and it won't interfere with your current shell ulimit settings. note: -v 1000000 corresponds to approximately 1GB of RAM


    2
    (ulimit -v 1000000; scriptname)
    alperyilmaz · 2011-01-27 21:30:59 6
  • Set laptop display brightness

    An alternative which does not require to be root


    2
    echo <percentage> | sudo dd of=/proc/acpi/video/VGA/LCD/brightness
    alperyilmaz · 2011-01-05 03:57:58 6
  • strip non-constant number of directories from tar archive while decompressing

    If you want to decompress the files from an archive to current directory by stripping all directory paths, use --transform option to strip path information. Unfortunately, --strip-components option is good if the target files have same and constant depth of folders. The idea was taken from http://www.unix.com/solaris/145941-how-extract-files-tar-file-without-creating-directories.html Show Sample Output


    1
    tar --transform 's#.*/\([^/]*\)$#\1#' -xzvf test-archive.tar.gz
    alperyilmaz · 2010-11-29 23:16:57 5
  • paste one file at a time instead of in parallel

    paste one file at a time instead of in parallel Show Sample Output


    2
    paste --serial file1 file2 file3
    alperyilmaz · 2010-10-27 08:17:41 5
  • Analyse writing style of writing style of a document

    Style analyses the surface characteristics of the writing style of a document. It prints various readability grades, length of words, sentences and paragraphs. It can further locate sentences with certain characteristics. If no files are given, the document is read from standard input. style is part of "diction" package Show Sample Output


    2
    style TEXT-FILE
    alperyilmaz · 2010-10-27 08:07:04 31
  • prevent accidents and test your command with echo

    if you're using wildcards * or ? in your command, and if you're deleting, moving multiple files, it's always safe to see how those wildcards will expand. if you put "echo" in front of your command, the expanded form of your command will be printed. It's better safe than sorry. Show Sample Output


    11
    echo rm *.txt
    alperyilmaz · 2010-10-27 07:26:26 6
  • exclude a column with cut

    Show all columns except 5th. This might help you save some typing if you are trying to exclude some columns from the output.


    24
    cut -f5 --complement
    alperyilmaz · 2010-10-21 20:21:07 14
  • most used commands in history (comprehensive)

    Most of the "most used commands" approaches does not consider pipes and other complexities. This approach considers pipes, process substitution by backticks or $() and multiple commands separated by ; Perl regular expression breaks up each line using | or < ( or ; or ` or $( and picks the first word (excluding "do" in case of for loops) note: if you are using lots of perl one-liners, the perl commands will be counted as well in this approach, since semicolon is used as a separator Show Sample Output


    4
    history | perl -F"\||<\(|;|\`|\\$\(" -alne 'foreach (@F) { print $1 if /\b((?!do)[a-z]+)\b/i }' | sort | uniq -c | sort -nr | head
    alperyilmaz · 2010-04-08 13:46:09 4
  • statistics in one line

    In this example, file contains five columns where first column is text. Variance is calculated for columns 2 - 5 by using perl module Statistics::Descriptive. There are many more statistical functions available in the module. Show Sample Output


    1
    perl -MStatistics::Descriptive -alne 'my $stat = Statistics::Descriptive::Full->new; $stat->add_data(@F[1..4]); print $stat->variance' filename
    alperyilmaz · 2010-04-02 21:16:12 6
  • Test speaker channels

    Useful tool to test if all speaker channels are working properly. speaker-test is part of alsa-utils package Show Sample Output


    5
    speaker-test -D plug:surround51 -c 6 -l 1 -t wav
    alperyilmaz · 2009-11-05 02:57:46 3
  • remove the last of all html files in a directory

    sed can be used deleting the last line and with -i option, there's no need to for temp files, the change is made on the actual file


    1
    for f in *.html; do sed '$d' -i "$f"; done
    alperyilmaz · 2009-10-12 14:46:43 4
  • count occurences of each word in novel David Copperfield

    This command might not be useful for most of us, I just wanted to share it to show power of command line. Download simple text version of novel David Copperfield from Poject Gutenberg and then generate a single column of words after which occurences of each word is counted by sort | uniq -c combination. This command removes numbers and single characters from count. I'm sure you can write a shorter version. Show Sample Output


    -4
    wget -q -O- http://www.gutenberg.org/dirs/etext96/cprfd10.txt | sed '1,419d' | tr "\n" " " | tr " " "\n" | perl -lpe 's/\W//g;$_=lc($_)' | grep "^[a-z]" | awk 'length > 1' | sort | uniq -c | awk '{print $2"\t"$1}'
    alperyilmaz · 2009-05-04 16:00:39 11
  • Explanation of system and MySQL error codes

    perror should be installed if mysql-server package is installed Show Sample Output


    1
    perror NUMBER
    alperyilmaz · 2009-03-31 19:19:44 4
  • sorting file contents into individual files with awk

    This command will sort the contents of FILENAME by redirecting the output to individual .txt files in which 3rd column will be used for sorting. If FILENAME contents are as follows: foo foo A foo bar bar B bar lorem ipsum A lorem Then two files called A.txt and B.txt will be created and their contents will be: A.txt foo foo A foo lorem ipsum A lorem and B.txt will be bar bar B bar


    2
    awk '{print > $3".txt"}' FILENAME
    alperyilmaz · 2009-03-31 15:14:13 6
  • Delete more than one month old thumbnails from home directory

    By time thumbnail images in ~/thumbnails take up too much space, this command will help deleting old ones. Find options explained: -type f : find files only, not directories -atime +30 : last accessed more than 30 days ago


    1
    find ~/.thumbnails/ -type f -atime +30 -print0 | xargs -0 rm
    alperyilmaz · 2009-03-30 04:23:07 12
  • Spell check the text in clipboard (paste the corrected clipboard if you like)

    xclip -o > /tmp/spell.tmp # Copy clipboard contents to a temp file aspell check /tmp/spell.tmp # Run aspell on that file cat /tmp/spell.tmp | xclip # Copy the results back to the clipboard, so that you can paste the corrected text I'm not sure xclip is installed in most distributions. If not, you can install x11-apps package


    2
    xclip -o > /tmp/spell.tmp; aspell check /tmp/spell.tmp ; cat /tmp/spell.tmp | xclip
    alperyilmaz · 2009-03-26 00:49:59 7
  • Clean swap area after using a memory hogging application

    When you run a memory intensive application (VirtualBox, large java application, etc) swap area is used as soon as memory becomes insufficient. After you close the program, the data in swap is not put back on memory and that decreases the responsiveness. Swapoff disables the swap area and forces system to put swap data be placed in memory. Since running without a swap area might be detrimental, swapon should be used to activate swap again. Both swapoff and swapon require root privileges.


    10
    swapoff -a ; swapon -a
    alperyilmaz · 2009-03-25 03:30:41 15
  • Remove leading zeros in multiple columns with sed

    Leading zeros might help correct sorting and they can be removed by sed after sorting Show Sample Output


    2
    sed 's/\b\(0*\)//g' filename
    alperyilmaz · 2009-03-24 20:19:42 10
  • Add thousand separator with sed, in a file or within pipe

    Does not necessarily require a file to process, it can be used in a pipe as well: cat filename | sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta' I don't remember where I copy/pasted this from, I wish I credited the original author Show Sample Output


    3
    sed -e :a -e 's/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta' filename
    alperyilmaz · 2009-03-24 20:06:02 6
  • raw MySQL output to use in pipes

    -N removes header -s removes separator chars -r raw output After using these options, the MySQL ouptut can be used with pipes very easily Show Sample Output


    8
    mysql DATABASE -N -s -r -e 'SQL COMMAND'
    alperyilmaz · 2009-03-24 19:53:46 5
  • View non-printing characters with cat

    Useful to detect number of tabs in an empty line, DOS newline (carriage return + newline). A tool that can help you understand why your parsing is not working. Show Sample Output


    4
    cat -v -t -e
    alperyilmaz · 2009-03-24 19:29:03 11
  • Passwordless mysql{,dump,admin} via my.cnf file

    The file .my.cnf located at user's home directory is used for mysql login. If this file exists, then mysql -uYOURUSERNAME -pYOURPASSWORD database -e 'SOME SQL COMMAND' can be replaced with mysql database -e 'SOME SQL COMMAND' It saves you from typing! This is valid for mysqladmin and mysqldump commands as well. Show Sample Output


    0
    echo -e "[client]\nuser = YOURUSERNAME\npassword = YOURPASSWORD" > ~/.my.cnf
    alperyilmaz · 2009-03-24 19:05:39 9

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doing some floating point math

Use curl with a local SOCKS5 proxy (e.g. Tor)
Routes curl input through a local SOCKS5 proxy; in this case, anonymizes curl activity via The Onion Router (Tor) proxy running locally. Note that the traffic will be anonymized, but it will NOT be encrypted, so your traffic will be very vulnerable to man-in-the-middle attacks.

Setup a persistant SSH tunnel w/ pre-shared key authentication
This creates a persistent ssh -i /path/to/key -ND local-IP:PORT User@Server connection. You may have to install autossh. -f puts in daemon mode. if you are having trouble, try it without -f.

Find usb device in realtime
Using this command you can track a moment when usb device was attached.

Change every instance of OLD to NEW in file FILE
Very quick way to change a word in a file. I use it all the time to change variable names in my PHP scripts (sed -i 's/$oldvar/$newvar/g' index.php)

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

Takes and displays screenshot of Android phone over adb.
Dependencies on phone: adb access, screencap command, base64 command. Dependencies on computer: adb, sed, base64, display (from imagemagick, but can substitute other image viewer which reads from stdin). This should work around adb stupidies (i.e. that it replaces \n with \r\n) with base64.

Extract rpm package name, version and release using some fancy sed regex
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!)

Combining text files into one file

Massive change of file extension (bash)
Change the file extension in batch. Useful to create output file names with same input name but distinct extension by including logic inside the loop

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