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  • Checking that Input or a Variable is an Integer in BASH
    08/26/2014 9:02AM

    Here is a quick snippet for checking whether or not a variable is a valid integer in BASH.  It is also a howto for regular expressions in a shell script.

    # Make sure that FOO is an integer
    if [[ ! "$FOO" =~ ^[0-9]+$ ]]; then
            echo "The FOO was NOT an integer"

  • How To Benchmark Disk I/O
    08/14/2014 12:24PM

    Here is a quick snipped on how to benchmark Disk I/O with dd.

    $ time sh -c "dd if=/dev/zero of=/home/rchapin/test.zeros bs=1024k count=10000 && sync"

    10000+0 records in
    10000+0 records out
    10485760000 bytes (10 GB) copied, 81.4124 s, 129 MB/s

    real    1m21.950s
    user    0m0.810s
    sys     0m5.474s

    Will do a write test of 10GB.

    You can do a similar test and read from that file generated and write to another file or /dev/null to get an idea of the read speeds.

    See the this link for more information.

  • Creating an Array in Bash from a File With Each Element on a Separate Line
    07/17/2014 8:38AM

    Let's say that you have a file and you would like to convert each line in the file to an element in an array.

    The key to this is knowing about and how to manipulate the IFS (Internal Field Separator).  The default IFS is whitespace (a space, tab, or newline) and if you create an array passing it a whitespace delimited list of strings, each token will be set to an element in the array.

    ARRAY=(a b d c)

    Will result in an array with a single letter in each element.

    To do the same thing with the contents of a file, whereby each element is on a separate line, the first thing to be done is to set the IFS that is just new-lines (carriage returns).  Then set, as the input for the array, the contents of the file.

    # Save our existing IFS

    # Set our IFS to a new-line/carriage return

    # Create the array with the contents of a file
    TEST_ARRAY=($(cat some_file.txt))

    # Reset our IFS

    for i in "${TEST_ARRAY[@]}"
       echo $i

  • Installing Chrome Extensions Without Signing in With a Google Account
    06/27/2014 10:49AM

    Google requires that you login with a Google account before you can install any Chrome extensions.

    The following is how to install an extension without logging in (under Windows.  The same should work under Linux and Mac):

    1. Find the ID for the extension.  When you browse the extension in the store you will see a URL similar to the following:  https://chrome.google.com/webstore/detail/cookies/iphcomljdfghbkdcfndaijbokpgddeno?hl=en.   The hash string after the 'cookies' string (the name of the extension) up to the ? is the id.
    2. Download the .crx extension file.  Use the following URL and replace the <ID> string with the ID for your extension:  https://clients2.google.com/service/update2/crx?response=redirect&x=id%3D<ID>%26uc.  Chrome will complain that the extension cannot be added from this site.  Just ignore/OK it and you will be able to download it.
    3. Download and install (if you don't already have it) 7zip.
    4. Create a directory and move the .crx file into it.  Go into that dir, rename the .crx file to .zip and use 7zip to extract the file.
    5. Then back in chrome enter the following URL:  chrome://extensions/
    6. Towards the top-right of the page, check the "Developer Mode" checkbox.
    7. Then click on the "Load unpacked extension..." button and navigate to the directory that contains the unpacked .crx file and select it and it should install the extension for you.
  • Removing The Last N Character From a String in Bash Script
    06/19/2014 5:28PM
    Here is a quick one-liner for trimming a specific number of characters from the end of a string under bash:

    # Remove the last 5 characters
    $ echo "somestringwith12345" | sed "s/.....$//g"
    $ somestringwith

    # Remove the last 3 characters
    $ echo "somestringwith12345" | sed "s/...$//g"
    $ somestringwith12
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