Commands by mkc (9)

  • This command is somewhat similar to 'nice', but constrains I/O usage rather than CPU usage. In particular, the '-c3' flag tells the OS to only allow the process to do I/O when nothing else is pending. This dramatically increases the responsiveness of the rest of the system if the process is doing heavy I/O. There's also a '-p' flag, to set the priority of an already-running process.


    6
    ionice -c3 find /
    mkc · 2009-02-19 17:23:12 3
  • The Linux /dev/full file simulates a "disk full" condition, and can be used to verify how a program handles this situation. In particular, several programming language implementations do not print error diagnostics (nor exit with error status) when I/O errors like this occur, unless the programmer has taken additional steps. That is, simple code in these languages does not fail safely. In addition to Perl, C, C++, Tcl, and Lua (for some functions) also appear not to fail safely. Show Sample Output


    8
    perl -e 'print 1, 2, 3' > /dev/full
    mkc · 2009-02-19 17:08:13 2
  • The backslash avoids any 'rm' alias that might be present and runs the 'rm' command in $PATH instead. In a misguided attempt to be more "friendly", some Linux distributions (or sites/etc.) alias 'rm' to 'rm -i'. Unfortunately, this trains users to expect that files won't actually be deleted until they okay it. This expectation will fail with catastrophic results when they use other distributions, move to other sites, etc., and doesn't really even work 100% even with the alias. It's too late to fix 'rm', but '\rm' should work everywhere (under bash).


    3
    \rm somefile
    mkc · 2009-02-19 16:55:54 0
  • This is the setup I'm using for my largest project. It gives 357 lines per page (per side), which makes it fairly easy to carry around a significant amount of code on a few sheets of paper. Try it. (I stick to the 80 column convention in my coding. For wider code, you'll have to adjust this.)


    1
    enscript -E -B -3 -r -s 0 --borders -fCourier4.8 --mark-wrapped-lines=arrow
    mkc · 2009-02-09 06:23:38 1
  • The date command does offset calculations nicely, handles concepts like "a month" as you'd expect, and is good for offsets of at least 100M years in either direction. Show Sample Output


    3
    date --date="1 fortnight ago"
    mkc · 2009-02-06 20:57:59 0
  • strace can be invaluable in trying to figure out what the heck some misbehaving program is doing. There are number of useful flags to limit and control its output, and to attach to already running programs. (See also 'ltrace'.) Show Sample Output


    5
    strace -f -s 512 -v ls -l
    mkc · 2009-02-06 02:45:33 0
  • This is priceless for discovering otherwise invisible characters in files. Like, for example, that stray Control-M at the end of the initial hash bang line in your script, which causes it to generate a mysterious error even though it looks fine. ('od' is the last word, of course, but for many purposes it's much harder to read.)


    0
    cat -A
    mkc · 2009-02-06 02:37:51 0
  • This is a quick and dirty way to generate a (non-floating-point) CPU-bound task to benchmark. Adjust "20" to higher or lower values, as needed. As a benchmark this is probably a little less bogus than bogomips, and it will run anywhere 'bc' does. Show Sample Output


    2
    echo '2^2^20' | time bc > /dev/null
    mkc · 2009-02-06 02:31:55 1
  • This command repeatedly gets the specified process' stack using pstack (which is an insanely clever and tiny wrapper for gdb) and displays it fullscreen. Since it updates every second, you rapidly get an idea of where your program is stuck or spending time. The 'tac' is used to make the output grow down, which makes it less jumpy. If the output is too big for your screen, you can always leave the 'tac' off to see the inner calls. (Or, better yet--get a bigger screen.) Caveats: Won't work with stripped binaries and probably not well with threads, but you don't want to strip your binaries or use threads anyway. Show Sample Output


    8
    watch -n 1 'pstack 12345 | tac'
    mkc · 2009-02-05 18:17:00 3

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Encrypt and password-protect execution of any bash script
(Please see sample output for usage) script.bash is your script, which will be crypted to script.secure script.bash --> script.secure You can execute script.secure only if you know the password. If you die, your script dies with you. If you modify the startup line, be careful with the offset calculation of the crypted block (the XX string). Not difficult to make script editable (an offset-dd piped to a gpg -d piped to a vim - piped to a gpg -c directed to script.new ), but not enough space to do it on a one liner.

Edit your command in vim ex mode by <ctrl-f>
If you are in ex mode in vim i.e. you've pressed ':'. You can edit the current command by pressing <ctrl-f>

Using mplayer to play the audio only but suppress the video

Show number of NIC's, ports per nic and PCI address

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.

Generate random number with shuf
If you don't have seq or shuf, bash can be used.

recursive base64 encoding -- Cipher for the Poor ?
Just for fun, I searched a simple way to encrypt some text. Simple base64 encoding seemed a good start so I decided to "amplify" encoding using repeted base64 encoding. Of course, this is not really secure but can be useful to hide datas to most part of humans ;). Do not hesitate to provide better solutions or else.

clone a hard drive to a remote directory via ssh tunnel, and compressing the image

Shorten any Url using bit.ly API, using your API Key which enables you to Track Clicks
Shorten any Url using bit.ly API, using your API Key which enables you to Track Clicks I have it as a Function in my .bash_aliases [code] shorten () { longUrl=$1; curl "http://api.bit.ly/shorten?version=2.0.1&longUrl=LONG_URL_YOU_WANT_SHORTENED&login=rungss&apiKey=" } [/code] Here is an Output showing the Function Detail.. [konsole] bijay@bijay:$ type shorten shorten is a function shorten () { longUrl=$1; curl "http://api.bit.ly/shorten?version=2.0.1&longUrl=$longUrl&login=rungss&apiKey=R_48d7e0b40835b09e3861bd455f7abec7" } [/konsole]

Coping files, excluding certain files
Preserve file structure when coping and exclude some file o dir patterns


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