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Posts Tagged ‘loop’

How to make for loop (cycles) in KSH useful for FreeBSD / UNIX system administrators

Friday, November 3rd, 2017

korn-shell-how-to-make-loops-easily-for-sys-admin-purposes

Sometimes we have to administrate this operating systems such as FreeBSD / AIX / HP UX or even Mac OS server where by default due to historical reasons or for security bash shell is not avialable. That's not a common scenario but it happens so if as sysadmin we need to create for loops on ksh it is useful to know how to do that, as for loop cycles are one of the most important command line tools the sysadmin swiss army knife kind of.

So how to create a for loop (cycle) in ksh (Korn Shell)?

The most basic example for a KSH loop shell is below:

#!/bin/ksh
for i in 1 2 3 4 5
do
echo "Welcome $i times"
done

Add the content to any file lets say ksh_loop.ksh then make it executable as you do in bash shells

$ chmod +x ksh_loop.ksh
$ ksh ksh_loop.ksh

The overall syntax of the for loop ksh command is as follows:

for {Variable} in {lists}
do
echo ${Variable}
done

Hence to list lets say 20 iterations in a loop in ksh you can use something like:

#!/bin/ksh
for i in {1..20}
do
echo "Just a simple echo Command $i times";
# add whatever system commands you like here
done

Example for some useful example with KSH loop is to list a directory content so you can execute whatever command you need on each of the files or directories inside

#!/bin/ksh
for f in $(ls /tmp/*)
do
print "Iterating whatever command you like on /tmp dir : $f"
done

Other useful for loop iteration would be to print a file content line by line just like it is done in bash shell, you can do that with a small loop like belows:

#!/bin/ksh
for iteration_variable in $(cat file_with-your-loved-content-to-iterate.txt)
do
print "Current iteration like is : $iteration_variable"
done

Tags: freebsd, loop, make, system, unix, Useful
Posted in FreeBSD, IBM AIX UNIX, Programming | No Comments »

Remove string line from file on Linux and BSD – Delete entire line with string from file

Tuesday, March 15th, 2016

linux-remove-lines-containing-string-with-sed

If you're already used too using grep -v "sometring" filename to print everything from a file without the certain grepped string output and you want to do the same to delete lines based on strings without having to output the grepped string to a file and then overwritting the original file:

grep -v 'whatever' filename > filename1
mv filename1 filename

A much better way to delete an whole line containing a string match from a file is to use sed
sed should be the tool of choice especially if you're scripting because sed is especially made for such batch edittings.

Here is how to do delete an entire line based on a given string:

sed –in-place '/some string to search and delete/d' myfilename

It might be a good idea to also create backups just to make sure something doesn't get deleted incidently to do use:

sed –in-place=.bak '/some string to search and delete/d' myfilename

If you need to wipe out an exact string from all files within a folder you might use a for loop or perl (some good examples check my previous article here)

In short to use bash's for loop here is how to backup and remove all lines with a string match within all files within a Linux directory:

for f in *.txt; do sed –in-place '/some string/d'
"$f"; done
find -name '*.txt' -exec sed –in-place=.bak '/some
string/d' "{}" ';'

BTW SED is really rich editor and some people got so much into it that there is even a sed written text (console) version of arkanoid 🙂

sed-text-editor-written-arkanoid-game-linux-bsd

If you want to break the ice and get some fun in your boring sysadmin life get sed arkanoid code from here.
I have it installed under pc-freak.net free ASCII Games entertainment service, so if you want to give it a try just login and give a try.

Enjoy 🙂

Tags: bak, file, good, life, line, loop, make, match, string, use
Posted in Linux, Remote System Administration, System Administration, Various | No Comments »

How to execute ssh command on multiple Linux servers with native ssh client and a bash loop – Changing shell terminal to multiple servers from ksh to bash

Monday, February 16th, 2015

how-to-execute-ssh-command-on-multiple-linux-servers-with-native-ssh-client-and-bash-loop-changing-default-shell-terminal-to-bash-for-mass-many-multiple-linux-unix-servers
I've been working for a customer that has about 450 hundred servers running all kind of different Web Applications / Mail services / FTP / Web Statistics etc.. I have a single user / password access to all of the servers (using LDAP authentication) – just like many of my colleagues and by default most of servers shell set is Korn Shell (/bin/ksh) is automatically run on ssh login time ( as it is set as the default shell ). I have nothing personally against Korn Shell but as mainly script in Bash Shell last 10+ years and I'm used to Bash's terminal behavior so much, each time I login to the servers I had to run manually run :

/bin/bash

This becomes really annoying, because I have to login to so many servers daily and do various stuff, so I got pissed off at the end and I wanted to change default shell set (only for my current) user to BASH, since there are other users that work on servers and its not a good idea to change globally servers global shell to bash, because such action could hurt some poor colleague love for KSH 🙂

A note to make here is the servers are primary running SuSE SLES / CentOS and Debian and RHEL Linux, but this bash one liner would be working on any other Linux release which has a bash >=2.0, I've tested it exactly on bash 3.2.25.

I have dump of all server hostnames / IPs in a plain text (.txt) file called all_servers_list.txt and since the servers are not accessible between each other but only through a special HOP station running Windows I couldn't install and use sshpass for mass deploy of new $SHELL variable configuration into home directory's $HOME/.profile ( ~/.profile ) . Thus I was forced to use a standard SSH client and a MobaXTERM inistallation which comes with integrated CygWin bash (for windows) and thus I can run normal Linux bash code inside the MobaXTerm Terminal on the Windows 2012R2 (jump host) .. 🙂

while read line; do ssh my-user@$line 'echo "export SHELL=/bin/bash ; exec /bin/bash" >> /home/my-user/.profile' < /dev/null; done < all_servers_list.txt

Since SSH client doesn't have a non-interactive way to pass on password from command line (for security reasons), to make above bash one liner loop to deploy bash as a default shell (mass) on all servers I have to paste (my Sotred in Memory Copied password) the SSH remote login server password 450 times each time I',m prompted by SSH to input password manually (this takes about 20) minutes but it is a worthy time, since from then on /bin/bash runs automatically on server login time. One important note to make is the </dev/null here is necessery because otherwise ssh is having troubles with reading the host in the loop. If you try running above cmd without </dev/null you, the loop is about to end after first login attempt. Changing default shell to multiple servers is not done only to servers with default ksh, but for any servers with default csh shell or any other obscure shell to bash (if bash is installed) is achieved by above command.

As you can guess above while bash loop, can easily be modified to run any other command to a bunch of hundred or thousand servers of your choise, the only inconvenience you will have is you have to paste the password for each server part of loop to which ssh is creating connection.
This example works on Linux but should work fine on any other platform that have /bin/bash (or /usr/local/bin/bash) installed if on FreeBSD / NetBSD, it should work on HP-UX and SunOS / Solaris hosts which have bash installed too.

Once you've launched the loop and added /bin/bash to run on login to check on next login where you're really running bash shell there is the:

echo $SHELL
/bin/bash

If you want keep / grep output of shell variable $SHELL:

MYSHELL=`ps -hp $$|awk '{echo $5}'`

Anyhow on some Linux hosts this variable might show bash and still you might be running old shell ksh / csh, the better way to check your SHELL is with ps -p $$ command (nowdays not known by many admins)

ps -p $$
PID TTY TIME CMD
866 pts/0 00:00:00 bash

Now I can happily use bash on all the servers every time I login. Cheers and Thanks God ! 🙂

Tags: bash shell, bin, current user, default shell, How to, KSH, liner, loop, multiple, server login, server password, servers, ssh client, ssh command
Posted in Curious Facts, Everyday Life, Programming, Remote System Administration, System Administration, Various | 1 Comment »

Linux watch Windows equivalent command bat script – How to Run a command every XXX seconds on Windows

Tuesday, May 27th, 2014

windows-watch-command-linux-watch-windows-equivalent-run-script-every-xxx-seconds-on-microsoft-windows
If you're a Linux administrator you're probably already quite used to watch command which allows to execute a program periodically, showing output fullscreen. Watch is very useful to run a specific command every XXX seconds, and see the results constantly updated. watch is very useful to keep an eye on growing files, i.e.: lets say keep an eye on SQL dump:

`watch "ls -al some-dump-file.sql"`

or keep an eye on how a directory keeps growing in real time

`watch -n 5 "du -hsc /tmp"`

Above command would tell watch to refresh du -hsc /tmp on a 5 seconds interval.

So a logical question pops up "Is there a command line equivalent to Linux's watch?" In Windows there is no native command equivalent of Linux watch but there is one liner bat (Batch) script to equivalent to emulate Linux watch in Windows. The Watch like script in Windows OS looks like so:

`@ECHO OFF :loop tasklist timeout /t 2 goto loop`

Use notepad and paste above batch script to any file and save it as whateverfile.bat, running it will make all processes to get listed occuring every 2 seconds (/t 2 – is an argumeent telling the loop to expire on every 2 seconds).

Modify the script to monitor whatever Windows command you like 🙂
Enjoy

Tags: command, eye, liner, Linux, logical question, loop, real time, running, script, Watch, Windows
Posted in Everyday Life, Programming, System Administration, Various, Windows | No Comments »

Tiny PHP script to dump your browser set HTTP headers (useful in debugging)

Friday, March 30th, 2012

While browsing I stumbled upon a nice blog article

Dumping HTTP headers

The arcitle, points at few ways to DUMP the HTTP headers obtained from user browser.
As I'm not proficient with Ruby, Java and AOL Server what catched my attention is a tiny php for loop, which loops through all the HTTP_* browser set variables and prints them out. Here is the PHP script code:

<?php 
foreach($_SERVER as $h=>$v) 
if(ereg('HTTP_(.+)',$h,$hp)) 
echo "<li>$h = $v</li>\n"; 
header('Content-type: text/html'); 
?>

The script is pretty easy to use, just place it in a directory on a WebServer capable of executing php and save it under a name like:
show_HTTP_headers.php

If you don't want to bother copy pasting above code, you can also download the dump_HTTP_headers.php script here , rename the dump_HTTP_headers.php.txt to dump_HTTP_headers.php and you're ready to go.

Follow to the respective url to exec the script. I've installed the script on my webserver, so if you are curious of the output the script will be returning check your own browser HTTP set values by clicking here.
PHP will produce output like the one in the screenshot you see below, the shot is taken from my Opera browser:

Screenshot show HTTP headers.php script Opera Debian Linux

Another sample of the text output the script produce whilst invoked in my Epiphany GNOME browser is:

HTTP_HOST = www.pc-freak.net
HTTP_USER_AGENT = Mozilla/5.0 (X11; U; Linux x86_64; en-us) AppleWebKit/531.2+ (KHTML, like Gecko) Version/5.0 Safari/531.2+ Debian/squeeze (2.30.6-1) Epiphany/2.30.6
HTTP_ACCEPT = application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
HTTP_ACCEPT_ENCODING = gzip
HTTP_ACCEPT_LANGUAGE = en-us, en;q=0.90
HTTP_COOKIE = __qca=P0-2141911651-1294433424320;
__utma_a2a=8614995036.1305562814.1274005888.1319809825.1320152237.2021;wooMeta=MzMxJjMyOCY1NTcmODU1MDMmMTMwODQyNDA1MDUyNCYxMzI4MjcwNjk0ODc0JiYxMDAmJjImJiYm; 3ec0a0ded7adebfeauth=22770a75911b9fb92360ec8b9cf586c9;
__unam=56cea60-12ed86f16c4-3ee02a99-3019;
__utma=238407297.1677217909.1260789806.1333014220.1333023753.1606;
__utmb=238407297.1.10.1333023754; __utmc=238407297;
__utmz=238407297.1332444980.1586.413.utmcsr=pc-freak.net|utmccn=(referral)|utmcmd=referral|utmcct=/blog/

You see the script returns, plenty of useful information for debugging purposes:
HTTP_HOST – Virtual Host Webserver name
HTTP_USER_AGENT – The browser exact type useragent returnedHTTP_ACCEPT – the type of MIME applications accepted by the WebServerHTTP_ACCEPT_LANGUAGE – The language types the browser has support for
HTTP_ACCEPT_ENCODING – This PHP variable is usually set to gzip or deflate by the browser if the browser has support for webserver returned content gzipping.
If HTTP_ACCEPT_ENCODING is there, then this means remote webserver is configured to return its HTML and static files in gzipped form.
HTTP_COOKIE – Information about browser cookies, this info can be used for XSS attacks etc. 🙂
HTTP_COOKIE also contains the referrar which in the above case is:
__utmz=238407297.1332444980.1586.413.utmcsr=pc-freak.net|utmccn=(referral)
The Cookie information HTTP var also contains information of the exact link referrar:
|utmcmd=referral|utmcct=/blog/

For the sake of comparison show_HTTP_headers.php script output from elinks text browser is like so:

* HTTP_HOST = www.pc-freak.net * HTTP_USER_AGENT = Links (2.3pre1; Linux 2.6.32-5-amd64 x86_64; 143x42) * HTTP_ACCEPT = */* * HTTP_ACCEPT_ENCODING = gzip,deflate * HTTP_ACCEPT_CHARSET = us-ascii, ISO-8859-1, ISO-8859-2, ISO-8859-3, ISO-8859-4, ISO-8859-5, ISO-8859-6, ISO-8859-7, ISO-8859-8, ISO-8859-9, ISO-8859-10, ISO-8859-13, ISO-8859-14, ISO-8859-15, ISO-8859-16, windows-1250, windows-1251, windows-1252, windows-1256, windows-1257, cp437, cp737, cp850, cp852, cp866, x-cp866-u, x-mac, x-mac-ce, x-kam-cs, koi8-r, koi8-u, koi8-ru, TCVN-5712, VISCII,utf-8 * HTTP_ACCEPT_LANGUAGE = en,*;q=0.1 * HTTP_CONNECTION = keep-aliveOne good reason, why it is good to give this script a run is cause it can help you reveal problems with HTTP headers impoperly set cookies, language encoding problems, security holes etc. Also the script is a good example, for starters in learning PHP programming.

Tags: AOL, arcitle, article, attention, Auto, blog, browser, code, code lt, content type, copy, debugging, download, Draft, dump, Dumping, ENCODING, ereg, freak, gecko, Gnome, gzip, host, host www, HTTP, image png, information, Java, khtml, linux x86, loop, nbsp, opera browser, php, php script, php txt, place, prints, quot, ruby, Safari, screenshot, script, script code, server, set variables, shot, show, squeeze, support, text, Tiny, type, unam, User, utmb, utmcsr, xml
Posted in Programming, System Administration | No Comments »

How to set a crontab to execute commands on a seconds time interval on GNU / Linux and FreeBSD

Sunday, October 30th, 2011

Have you ever been in need to execute some commands scheduled via a crontab, every let’s say 5 seconds?, naturally this is not possible with crontab, however adding a small shell script to loop and execute a command or commands every 5 seconds and setting it up to execute once in a minute through crontab makes this possible.
Here is an example shell script that does execute commands every 5 seconds:

#!/bin/bash
command1_to_exec='/bin/ls'; command2_to_exec='/bin/pwd'; for i in $(echo 1 2 3 4 5 6 7 8 9 10 11); do sleep 5; $command1_to_exec; $command2_to_exec; done

This script will issue a sleep every 5 seconds and execute the two commands defined as $command1_to_exec and $command2_to_exec

Copy paste the script to a file or fetch exec_every_5_secs_cmds.sh from here

The script can easily be modified to execute on any seconds interval delay, the record to put on cron to use with this script should look something like:

# echo '* * * * * /path/to/exec_every_5_secs_cmds.sh' | crontab -

Where of course /path/to/exec_every_5_secs_cmds.sh needs to be modified to a proper script name and path location.

Another way to do the on a number of seconds program / command schedule without using cron at all is setting up an endless loop to run/refresh via /etc/inittab with a number of predefined commands inside. An example endless loop script to run via inittab would look something like:

while [ 1 ]; do /bin/ls sleep 5; done

To run the above sample never ending script using inittab, one needs to add to the end of inittab, some line like:

mine:234:respawn:/path/to/script_name.sh

A quick way to add the line from consone would be with echo:

echo 'mine:234:respawn:/path/to/script' >> /etc/inittab

Of course the proper paths, should be put in:

Then to load up the newly added inittab line, inittab needs to be reloaded with cmd:

# init q

I've also red, some other methods suggested to run programs on a periodic seconds basis using just cron, what I found in stackoverflow.com's as a thread proposed as a solution is:

* * * * * /foo/bar/your_script * * * * * sleep 15; /foo/bar/your_script * * * * * sleep 30; /foo/bar/your_script * * * * * sleep 45; /foo/bar/your_script

One guy, even suggested a shorted way with cron:

0/15 * * * * * /path/to/my/script

Tags: bashcommand, basis, com, command, command2, copy, copy paste, course, cron, crontab, echo 1, echo echo, endless loop, exec, file, foo, foo bar, freebsd, gnu linux, How to, init, inittab, interval, line, Linux, location, loop, mine, minute, name, nbsp, number, Path, predefined commands, pwd, record, refresh, respawn, run, script, script name, secs, SHA, Shell, shell script, sleep, something, stackoverflow, thread, time, time interval, way
Posted in Linux, Linux and FreeBSD Desktop, System Administration, Various | 1 Comment »

A Black and White Story and To Download an Apple a nice artistic videos produced by a friend

Tuesday, April 26th, 2011

Here are two really nice videos produced by Daniela Popova.

One is called Black and White Story and the other one is with the funny name To Download an Apple

The videos was produced for her Graduation assignment in NATFA (National Academy of Theater and Film arts).
Even better the Black and White Story Video has been selected for the Festival of the Orthodox Christian Cinema in Moscow.
The movie was selected by a the jury on the festival (a professor) who realized there is a deeper spiritual meaning behind the Black and White Story

The Black & White Story Video has also an outstanding bulgarian national folklore music combined with some modern day music, just check it out and enjoy.

The second movie To Download an Apple is a humorous one and I believe presents the sometimes stupid and serious efforts we do to follow fake imaginative goals.

Black and White Story

Daniela | Myspace Video

Black and White Story

To Download an Apple

As Daniela is a Christian the movies contain also a hidden Christian messages 😉
I greet her for the great work! Considering the uniqueness of the videos it’s obvious Daniela is really talented!
I’m looking forward to see some more from her works.

Tags: apple, assignment, autorewind, black, check, christian messages, cinema, clicktarget, clickurl, description, download, Festival, Film, film arts, FLOWPLAYER, flvmovie, folklore, folklore music, freak, funny name, Graduation, graduation assignment, having fun, height, jury, loop, modern day music, moscow, movie, music, Myspace, name, NATFA, National, national academy, national folklore, NATVIS, nbsp, Orthodox, player, spiritual, splashimage, story, StoryDaniela, swf, uniqueness, White, work
Posted in Entertainment, Everyday Life, Various | No Comments »

☩ Walking in Light with Christ – Faith, Computing, Diary

Posts Tagged ‘loop’

How to make for loop (cycles) in KSH useful for FreeBSD / UNIX system administrators

Tiny PHP script to dump your browser set HTTP headers (useful in debugging)

A Black and White Story and To Download an Apple a nice artistic videos produced by a friend

Daily Bible quote

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