Month: January 2008

Posted on

receive notification when file arrives

[problem]

You want to get notified when a file arrives. Maybe it is coming in from somewhere else, or just is the result of some processing.

What ever the case, never sit there waiting for a file to arrive again! 🙂

[/problem]

[solution]

Put the code under example tab, in a cron entry. See reference for more detail about cron.

Change the minutes, hour, filename and mail address! 🙂 You may need to use mail instead of mailx and ksh, etc instead of bash. But the basic syntax is the same. 🙂

[/solution]

[example]


0-59 12 * * * bash -c "([ -f $HOME/test-touch ] &&
mailx -s "test-touch found at `date`" [email protected]

[/example]

[reference]

[tags]cron, UNIX Batch, UNIX Scripts, Unix Coding School[/tags]

[/reference]

Posted on

UNIX debugging

[problem]

  1. You want to debug a running process on Solaris?
  2. You want to debug running process on Linux?

[/problem]

[solution]

See the example for debugging processes on Solaris or Linux – the syntax shows all system executes and reads.

[/solution]

[example]

  1. truss -xall -vall -rall -t'read' -p PID #

    To run a command and have it produce debug info, run it prefix with the truss syntax:

    truss -xall -vall -rall -t'read' your command #

    Another good option when debugging, is to run truss and look at the opens. Or more specifically the failures – as this often highlights missing libraries or permissions issues.

    truss -t'open' -p PID #

  2. On Linux use strace, which takes basically the same options. You just use -e, like this:

    strace -e'open' ls
    open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or directory)
    open("/etc/ld.so.cache", O_RDONLY) = 3
    open("/lib/tls/librt.so.1", O_RDONLY) = 3
    open("/lib/libtermcap.so.2", O_RDONLY) = 3
    open("/lib/libacl.so.1", O_RDONLY) = 3
    open("/lib/tls/libc.so.6", O_RDONLY) = 3
    open("/lib/tls/libpthread.so.0", O_RDONLY) = 3
    open("/lib/libattr.so.1", O_RDONLY) = 3
    open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
    open(".", O_RDONLY|O_NONBLOCK|O_LARGEFILE|O_DIRECTORY) = 3
    open("/etc/mtab", O_RDONLY) = 3
    open("/proc/meminfo", O_RDONLY) = 3

[/example]

[reference]

[tags]UNIX Debugging, Solaris Debugging, Linux Debugging, truss, strace, Unix Coding School[/tags]

[/reference]

Posted on

Smallest AJAX example in the world?

[problem]

Learn and demonstrate some simple AJAX.

To produce a clear, clean example – as small as possible.

[/problem]

[solution]

Can a smaller working AJAX example be produced?

Always a believer in keeping it simple & find it easier to learn something complex, by making it as small as possible. See Example.

[/solution]

[example]

  1. Click ‘see demo’.
  2. Click image to see updated date.
  3. Click ‘view the code’.

Here is the code:

<?php

if(isset($_GET['subreq'])) {
echo date('l dS of F Y h:i:s A');
exit(0);
}
?>
<img src=/icons/a.png onClick="javascript:
var xmlhttp=false;
/*@cc_on @*/
/*@if (@_jscript_version >= 5)
try {
xmlhttp = new ActiveXObject('Msxml2.XMLHTTP');
} catch (e) {
try { xmlhttp = new ActiveXObject('Microsoft.XMLHTTP'); } catch (E) { xmlhttp = false; }
}
@end @*/
if(!xmlhttp) { xmlhttp=new XMLHttpRequest(); }
xmlhttp.open('GET','index.php?subreq=y', true);
xmlhttp.onreadystatechange = function() {
if(xmlhttp.readyState==4) { document.getElementById('output_div').innerHTML = xmlhttp.responseText; }
}
xmlhttp.send(null);
">
<div id='output_div'>click image above to put date here</div>

Or Click this link:

[/example]

[reference]

[tags]AJAX tutorial, AJAX, AJAX demonstration, PHP, Learn AJAX[/tags]

For excellent doco (as always) check out Wiki.

[/reference]

Posted on

Shell Tips and Tricks

[problem]

  1. You want to trace program execution on Solaris?
  2. You want to perform network tracing on Solaris?
  3. Perform a text dump of a binary file – or see ascii codes, etc?
  4. Generate some random data?
  5. List directory contents in 3 columns?
  6. Loop through a list of files and perform actions on them?
  7. Check for values in vars?
  8. Detach a process without it dying.
  9. Perform arithmetic in shell.

[/problem]

[solution]

Some of the most useful Shell Tricks I’ve learned – check them out at Example – enjoy! 🙂

[/solution]

[example]

  1. System process debug (solaris) all exec/reads

    truss -xall -vall -rall -t'read' -p PID

  2. Network trace connection from hostname (solaris)

    snoop -x0 src hostname

  3. Optical dump of a file, useful for seeing control chars, etc and lines with no newline.

    od -c filename

  4. Generate 512 bytes of random data, cat -ve escapes control chars.

    dd bs=1 count=512 if=/dev/urandom | cat -ve

  5. list directory contents, display in 3 columns.

    ls | paste - - -

  6. Loop through all files and perform an action on it.

    for na in * ; do echo $na ; done

  7. Check for values in vars.

    [[ $(echo $var | grep -ic "pattern") -eq 0 ]] &

    You could also go for “-eq 1” – does contain or -ne 0 for same, etc. Plus you could use || for “or” either in place of “&&” or after this block – same as if .. then “positive” else “negative” fi.

  8. Detach a process without it dying.

    disown [%1]

    nohup command > /tmp/logfile.log 2>&1&

    If you start a process with nohop (ignore the hup signal), it will not exist (usually) when your shell is exited. This can now be simulated on solaris, by backgrounding a process (with ctrl Z and bg) then typing disown. jobs command will show all backgrounded jobs. Ideally start commands like this, to avoid the shell exit problem:

  9. Perform arithmetic in shell.

    bc -l

    Binary Calculator in long format – for float, etc. Can also be automated like this, to convert between decimal and hex:

    i=0; while ((i<20)) ; do echo -n "$i: "; echo "base=10;obase=16;$i" | bc; ((i++)); done | paste - - - -
    0: 0 1: 1 2: 2 3: 3
    4: 4 5: 5 6: 6 7: 7
    8: 8 9: 9 10: A 11: B
    12: C 13: D 14: E 15: F
    16: 10 17: 11 18: 12 19: 13

[/example]

[reference]

[tags]Unix Shell Tips, Unix Shell Tricks, UNIX Arithmetic, Optical Dump, Unix Coding School[/tags]

[/reference]