Syslog server

With all of the network configuration I’ve been doing lately, I’ve decided to set up a central syslog server that the routers and switches can log to. That will create a central place that I can look for warnings and errors that are occurring on these devices. It also makes it so I can save the logs for extended periods of time, and use normal Linux tools to search and parse through them.

For some reason, I found it difficult to find instructions on how to create a centralized syslog server. However, its incredibly easy. You just have to configure the Linux syslogd process to listen on a remote interface, then configure the logs like anything else in syslog. In CentOS, you just edit /etc/sysconfig/syslog and add a “-r” to the “SYSLOGD_OPTIONS” line. Then allow port 514 through your firewall from your router’s IP addresses.

On each router, set these global configuration commands:

logging facility local1
logging source-interface FastEthernet0/1
logging 10.0.0.123

On the syslog server, configure your /etc/syslog.conf with something like this:

## Router Logs
local1.* /var/log/routers/router-core.log
local2.* /var/log/routers/router-border.log
local3.* /var/log/routers/switch-1.log
local4.* /var/log/routers/switch-2.log

I also like to set up logrotate with this in /etc/logrotate.d/routers

/var/logs/routers/*.log {
weekly
rotate 52
compress
missingok
notifempty
}

ccde

• Routing TCP/IP, Volume 1, 2nd Edition
• Routing TCP/IP, Volume II
• MPLS and VPN Architectures, CCIP Edition
• MPLS Fundamentals
• Advanced MPLS Design and Implementation
• Definitive MPLS Network Designs
• Fault-Tolerant IP and MPLS Networks
• Traffic Engineering with MPLS
• QoS for IP/MPLS Networks
• Layer 2 VPN Architectures
• OSPF Network Design Solutions, 2nd Edition
• Optimal Routing Design
• BGP Design and Implementation
• Top-Down Network Design, 2nd Edition
• Troubleshooting IP Routing Protocols
• End-to-End QoS Network Design
• IP Quality of Service
• Network Management Fundamentals
• Voice-Enabling the Data Network
-rfc：
• Graceful Restart Mechanism for BGP
• BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)
• A Border Gateway Protocol 4 (BGP-4)
• Capabilities Advertisement with BGP-4
• Autonomous System Confederations for BGP
• Use of OSI IS-IS for Routing in TCP/IP and Dual Environments
• IS-IS Mesh Groups
• The OSPF Not-So-Stubby Area (NSSA) Option
• Alternative Implementations of OSPF Area Border Routers
• OSPF Version 2
• Protocol Independent Multicast - Sparse Mode (PIM-SM):Protocol Specification (Revised)
• Anycast-RP Using Protocol Independent Multicast (PIM)
• The Generalized TTL Security Mechanism (GTSM)
• BGP/MPLS IP Virtual Private Networks (VPNs)

find problems

First let me say that a complete format and reinstall will be necessary when your done doing forensics.

Probably good places to start looking would be to take a look at the apache/httpd logs for any abnormal error messages. Also look through the general system logs for anything suspicious. You should definitely download and run rootkit hunter and chkrootkit on the system, as there are a bunch of things listening as services that shouldn't be (like init for example), which makes a rootkit likely. If that's the case, then you may need to use a cd-based distro like knoppix-std or FIRE to do any further analysis.

You may have some luck looking those processes up by their process ID number in /proc//cmdline. If you find anything interesting there (like a path to the binary) take a look at the contents and see what you can find.

ssh

1. Generate a public/private key pair on the local machine
(ssh client): >
ssh-keygen -t rsa
(saving the file in ~/.ssh/id_rsa as prompted)

2. Just hit the when asked for passphrase (twice) for no
passphrase. If you do use a passphrase, you will also need to use
ssh-agent so you only have to type the passphrase once per session.
If you don't use a passphrase, simply logging onto your local
computer or getting access to the keyfile in any way will suffice
to access any ssh servers which have that key authorized for login.

3. This creates two files: >
~/.ssh/id_rsa
~/.ssh/id_rsa.pub

4. On the target machine (ssh server): >
cd
mkdir -p .ssh
chmod 0700 .ssh

5. On your local machine (ssh client): (one line) >
ssh {serverhostname}
cat '>>' '~/.ssh/authorized_keys2' < ~/.ssh/id_rsa.pub

or, for OpenSSH, (one line) >
ssh {serverhostname}
cat '>>' '~/.ssh/authorized_keys' < ~/.ssh/id_rsa.pub

You can test it out with >
ssh {serverhostname}
and you should be log onto the server machine without further need to type
anything.

If you decided to use a passphrase, do: >
ssh-agent $SHELL
ssh-add
ssh {serverhostname}
You will be prompted for your key passphrase when you use ssh-add, but not
subsequently when you use ssh.

Export and Backup Emails from Outlook to Gmail Online

It's possible to download emails from gmail into Outlook but is it possible to do it in reverse? Amit tells us we can in this step by step guide.

Step 1: Enable IMAP in your Gmail account and then
configure Outlook (or Outlook Express or Windows Live Mail) to sync
with your Gmail address via IMAP. Read this guide.

Step 2: Import your Outlook PST file into a Personal folder that is different from your default Gmail Inbox.

To import, click File -> Import And Export -> Import from another program or file. -> Next -> Personal Folder File (.pst)
-> Next.

Select the PST file that contains your email, then pick the email folders that you want to import in Outlook and click Finish.

Step 3: Select the Personal folders that you want to backup online and copy them your Gmail Folder in Outlook.

In the Folder List, right-click the folder you want to copy and click Copy Folder name. Click the Gmail Folder in Outlook to copy that folder in that location. You can repeat the steps as needed for other folders.

That's it!

How to reset my Joomla administrator password?

Joomla's admin username can be easily changed with a simple MySQL query. The most convenient way to manage the database is through the phpMyAdmin tool. Go to your cPanel and click on phpMyAdmin in the Databases box. (If you are not using cPanel or do not have phpMyAdmin, you can run the query directly for Joomla's database.)

Once in the phpMyAdmin select the Joomla database from the drop-down menu at left. The page will refresh and the database's tables will be displayed on it. Open the SQL tab (look at the top navigation bar).

In the text field write the following SQL query:

UPDATE `jos_users` SET `password` = MD5( 'new_password' ) WHERE `jos_users`.`username` = "admin" ;

"new_password" - replace this with the new password you wish to use.
"admin" - replace this if your admin username is different.

Once you are ready, click on the GO button to submit the query. If everything goes fine without errors, you should be able to login to Joomla with the new password.

Note: These instructions are valid both for Joomla 1.5 and Joomla 1.0.*.



If you have problems resetting the password yourself, ask your host for assistance. SiteGround provides the best Joomla hosting and such requests are handled with ease.

lamp/bind/ntp

Install CentOS 5.2 as a server (LAMP/Bind/ntp)
Posted by aristomagnus on Oct 28, 2008 in Featured, HowTo - Linux • 8 comments
Partition:

/dev/sda1 => ext3 -> /boot -> 128MB

/dev/sda2 => ext3 -> / -> 32768MB

/dev/sda3 => swap -> 2048MB

/dev/sda4 => ext3 -> /tmp -> Space left.

Disable IPv6 support if not needed.

-PACKAGE CONFIGURATION:
* Choose SERVER Templates.
* In the bottom, check CUSTOMIZE NOW.

-PACKAGES CUSTOMIZATION:
* In DEVELOPMENT: add DEVELOPMENT LIBRARIES, DEVELOPMENT TOOLS, LEGACY SOFTWARE DEVELOPMENT.
* In SERVER: uncheck everything (remove all packages).

* In BASE SYSTEM: add LEGACY SOFTWARE SUPPORT.

reboot

Edit /etc/selinux/config

Change the line:

SELINUX=enforcing

to

SELINUX=disabled

OR

system-config-securitylevel

Disable Security Level and SeLinux disabled

save and reboot

yum -y update

reboot

Disable service: ip6tables iptables bluetooth

chkconfig –levels 0123456 ip6tables off

chkconfig –levels 0123456 iptables off

chkconfig –levels 0123456 bluetooth off

To install a DNS server

yum -y install bind-chroot

To install MySQL server

yum -y install mysql mysql-devel mysql-server

To install php and perl:

yum -y install php php-devel php-gd php-imap php-ldap php-mysql php-odbc php-pear php-xml php-xmlrpc curl curl-devel perl-libwww-perl ImageMagick libxml2 libxml2-devel perl

Configure BIND9 (chrooted DNS Server)

BIND will run in a chroot jail under /var/named/chroot/var/named/ to allow BIND management via ISPConfig.

chmod 755 /var/named/

chmod 775 /var/named/chroot/

chmod 775 /var/named/chroot/var/

chmod 775 /var/named/chroot/var/named/

chmod 775 /var/named/chroot/var/run/

chmod 777 /var/named/chroot/var/run/named/

cd /var/named/chroot/var/named/

ln -s ../../ chroot

cp /usr/share/doc/bind-9.3.4/sample/var/named/named.local /var/named/chroot/var/named/named.local

cp /usr/share/doc/bind-9.3.4/sample/var/named/named.root /var/named/chroot/var/named/named.root

touch /var/named/chroot/etc/named.conf

Enter chkconfig –levels 235 named on

Configure MySQL

Enter chkconfig –levels 235 mysqld on

Note: Consider reviewing the MySQL Tuning guide and Low memory MySQL / Apache configurations for additional MySQL configuration suggestions.

Configure Apache

Modify the DirectoryIndex directive in your httpd.conf file:

vi /etc/httpd/conf/httpd.conf

Locate the DirectoryIndex for your web root

Modify the line to read as follows:

DirectoryIndex index.html index.htm index.shtml index.cgi index.php index.php3 index.pl

Find the line

Options Indexes FollowSymLinks

Remove Indexes from that line

Options FollowSymLinks

Exit vi

chkconfig –levels 235 httpd on

to start Apache whenever your server boots

Test Your Configuration

BIND

/etc/init.d/named restart

MySQL

/etc/init.d/mysqld start

netstat -tap | grep mysql

- if a line with the word LISTEN displays, MySQL was configured successfully and is now running

mysqladmin -u root password

(where is the unique password for your MySQL root account)

clear history

history -c

Add repository to yum:

Howto Repo: http://wiki.centos.org/AdditionalResources/Repositories

—————

FROM RPMforge: http://wiki.centos.org/AdditionalResources/Repositories/RPMForge

1. CentOS 5

You should make sure that you have Priorities installed.

1.1. Priorities

yum install yum-priorities

i386 http://apt.sw.be/redhat/el5/en/i386/RPMS.dag/rpmforge-release-0.3.6-1.el5.rf.i386.rpm

x86_64 http://apt.sw.be/redhat/el5/en/x86_64/RPMS.dag/rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm

(You can find a complete list of rpmforge-release package packages at http://dag.wieers.com/packages/rpmforge-release/ but it is recommended that you use one of the two listed above).

x64:

rpm -ivh http://apt.sw.be/redhat/el5/en/x86_64/RPMS.dag/rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm

Test with this command:

yum check-update

yum update

yum -y install phpmyadmin php-mcrypt php-mbstring

vi /usr/share/phpmyadmin/config.inc.php

Fine the line :

$cfg['blowfish_secret'] = ”; /* YOU MUST FILL IN THIS FOR COOKIE

AUTH! */

add a secret in the bracket. save the file.

Now you need to configure the access of phpmyadmin:

vi /etc/httpd/conf.d/phpmyadmin.conf


Order Deny,Allow
#Deny from all
Allow from all


/etc/init.d/httpd restart

Try it: http://ipoftheserver/phpmyadmin

user: root

passwd: your password

Synchronize The System Clock

If you want to have the system clock synchronized with an NTP server do the following:

yum install ntp

chkconfig –levels 235 ntpd on

ntpdate 0.pool.ntp.org

/etc/init.d/ntpd start

Install Webmin

cd /tmp

wget http://prdownloads.sourceforge.net/webadmin/webmin-1.441-1.noarch.rpm

rpm -ivh webmin-1.441-1.noarch.rpm

access webmin:

https://ipoftheserver:10000

Some infos are from: http://wiki.vpslink.com/HOWTO:_CentOS_5_setup_for_LAMP_and_ISPconfig#Step-by-step_Installation_Guide

Some infos are from: http://howtoforge.net/perfect-server-centos-5.2-x86_64

static ip in linux

vi /etc/sysconfig/network-scripts/ifcfg-eth0


Code:
DEVICE=eth0
BOOTPROTO=static
HWADDR=00:11:85:BC:7D:5F (YOUR NIC MAC ADDRESS)
IPADDR=111.111.111.111
NETMASK=255.255.255.0
ONBOOT=yes
TYPE=Ethernet
vi /etc/sysconfig/network


Code:
NETWORKING=yes
HOSTNAME=YOURDOMAIN.com (locoalhost.localdomain)
GATEWAY=111.111.111.111

centos- yum

Installing Apache, PHP, and MySQL on Fedora Core

This will install the basic components for a dynmaic, database-driven web site. We use yum to handle dependencies and gather all of the required packages.


1. Install Apache (httpd), PHP, MySQL (server and client), and the component that allows php to talk to mysql.

yum -y install httpd php mysql mysql-server php-mysql

2. Configure the new services to start automatically

/sbin/chkconfig httpd on
/sbin/chkconfig --add mysqld [this is not required with FC4 and above]
/sbin/chkconfig mysqld on

/sbin/service httpd start
/sbin/service mysqld start


3. IMPORTANT! Set up the mysql database root password. Without a password, ANY user on the box can login to mysql as database root. The mysql root account is a separate password from the machine root account.


mysqladmin -u root password 'new-password' [quotes are required]


4. Make additional security-related changes to mysql.
mysql -u root -p

mysql> DROP DATABASE test; [removes the test database]
mysql> DELETE FROM mysql.user WHERE user = ''; [Removes anonymous access]
mysql> FLUSH PRIVILEGES;

5. Following the above steps, the document root for Apache is /var/www/html/

Create a test PHP script (such as phpinfo.php) and place it in the document root. A useful test script sample:
phpinfo();
?>

6. Create a database and database user for your data. You will use this database and user name in your database connection string. The GRANT statement actually creates a new MySQL user account.
mysql> CREATE DATABASE web_db;
mysql> GRANT ALL PRIVILEGES ON web_db.* TO 'web_user'@'localhost' IDENTIFIED BY 'thepassword';

shell script

How to write a shell script
Introduction
A shell is a command line interpretor. It takes commands and executes them. As such, it implements a programming language. The Bourne shell is used to create shell scripts -- ie. programs that are interpreted/executed by the shell. You can write shell scripts with the C-shell; however, this is not covered here.

Creating a Script
Suppose you often type the command

find . -name file -print

and you'd rather type a simple command, say

sfind file

Create a shell script

% cd ~/bin
% emacs sfind
% page sfind
find . -name $1 -print
% chmod a+x sfind
% rehash
% cd /usr/local/bin
% sfind tcsh
./shells/tcsh

Observations
This quick example is far from adequate but some observations:

1. Shell scripts are simple text files created with an editor.
2. Shell scripts are marked as executeable

%chmod a+x sfind

3. Should be located in your search path and ~/bin should be in your search path.
4. You likely need to rehash if you're a Csh (tcsh) user (but not again when you login).
5. Arguments are passed from the command line and referenced. For example, as $1.

#!/bin/sh
All Bourne Shell scripts should begin with the sequence

#!/bin/sh

From the man page for exec(2):

"On the first line of an interpreter script, following the "#!", is the name of a program which should be used to interpret the contents of the file. For instance, if the first line contains "#! /bin/sh", then the con- tents of the file are executed as a shell script."

You can get away without this, but you shouldn't. All good scripts state the interpretor explicitly. Long ago there was just one (the Bourne Shell) but these days there are many interpretors -- Csh, Ksh, Bash, and others.
Comments
Comments are any text beginning with the pound (#) sign. A comment can start anywhere on a line and continue until the end of the line.
Search Path
All shell scripts should include a search path specifica- tion:

PATH=/usr/ucb:/usr/bin:/bin; export PATH

A PATH specification is recommended -- often times a script will fail for some people because they have a different or incomplete search path.

The Bourne Shell does not export environment variables to children unless explicitly instructed to do so by using the export command.
Argument Checking
A good shell script should verify that the arguments sup- plied (if any) are correct.

if [ $# -ne 3 ]; then
echo 1>&2 Usage: $0 19 Oct 91
exit 127
fi

This script requires three arguments and gripes accordingly.

Exit status
All Unix utilities should return an exit status.

# is the year out of range for me?

if [ $year -lt 1901 -o $year -gt 2099 ]; then
echo 1>&2 Year \"$year\" out of range
exit 127
fi

etc...

# All done, exit ok

exit 0

A non-zero exit status indicates an error condition of some sort while a zero exit status indicates things worked as expected.

On BSD systems there's been an attempt to categorize some of the more common exit status codes. See /usr/include/sysexits.h.
Using exit status
Exit codes are important for those who use your code. Many constructs test on the exit status of a command.

The conditional construct is:

if command; then
command
fi

For example,

if tty -s; then
echo Enter text end with \^D
fi

Your code should be written with the expectation that others will use it. Making sure you return a meaningful exit status will help.
Stdin, Stdout, Stderr
Standard input, output, and error are file descriptors 0, 1, and 2. Each has a particular role and should be used accordingly:

# is the year out of range for me?

if [ $year -lt 1901 -o $year -gt 2099 ]; then
echo 1>&2 Year \"$year\" out of my range
exit 127
fi

etc...

# ok, you have the number of days since Jan 1, ...

case `expr $days % 7` in
0)
echo Mon;;
1)
echo Tue;;

etc...

Error messages should appear on stderr not on stdout! Output should appear on stdout. As for input/output dialogue:

# give the fellow a chance to quit

if tty -s ; then
echo This will remove all files in $* since ...
echo $n Ok to procede? $c; read ans
case "$ans" in
n*|N*)
echo File purge abandoned;
exit 0 ;;
esac
RM="rm -rfi"
else
RM="rm -rf"
fi

Note: this code behaves differently if there's a user to communicate with (ie. if the standard input is a tty rather than a pipe, or file, or etc. See tty(1)).
Language Constructs

For loop iteration

Substitute values for variable and perform task:

for variable in word ...
do
command
done

For example:

for i in `cat $LOGS`
do
mv $i $i.$TODAY
cp /dev/null $i
chmod 664 $i
done

Alternatively you may see:

for variable in word ...; do command; done

* Case

Switch to statements depending on pattern match

case word in
[ pattern [ | pattern ... ] )
command ;; ] ...
esac

For example:

case "$year" in

[0-9][0-9])
year=19${year}
years=`expr $year - 1901`
;;
[0-9][0-9][0-9][0-9])
years=`expr $year - 1901`
;;
*)
echo 1>&2 Year \"$year\" out of range ...
exit 127
;;
esac

* Conditional Execution

Test exit status of command and branch

if command
then
command
[ else
command ]
fi

For example:

if [ $# -ne 3 ]; then
echo 1>&2 Usage: $0 19 Oct 91
exit 127
fi

Alternatively you may see:

if command; then command; [ else command; ] fi

* While/Until Iteration

Repeat task while command returns good exit status.

{while | until} command
do
command
done

For example:

# for each argument mentioned, purge that directory

while [ $# -ge 1 ]; do
_purge $1
shift
done

Alternatively you may see:

while command; do command; done

* Variables

Variables are sequences of letters, digits, or underscores beginning with a letter or underscore. To get the contents of a variable you must prepend the name with a $.

Numeric variables (eg. like $1, etc.) are positional vari- ables for argument communication.

o Variable Assignment

Assign a value to a variable by variable=value. For example:

PATH=/usr/ucb:/usr/bin:/bin; export PATH

or

TODAY=`(set \`date\`; echo $1)`

o Exporting Variables

Variables are not exported to children unless explicitly marked.

# We MUST have a DISPLAY environment variable

if [ "$DISPLAY" = "" ]; then
if tty -s ; then
echo "DISPLAY (`hostname`:0.0)? \c";
read DISPLAY
fi
if [ "$DISPLAY" = "" ]; then
DISPLAY=`hostname`:0.0
fi
export DISPLAY
fi

Likewise, for variables like the PRINTER which you want hon- ored by lpr(1). From a user's .profile:

PRINTER=PostScript; export PRINTER

Note: that the Cshell exports all environment variables.

o Referencing Variables

Use $variable (or, if necessary, ${variable}) to reference the value.

# Most user's have a /bin of their own

if [ "$USER" != "root" ]; then
PATH=$HOME/bin:$PATH
else
PATH=/etc:/usr/etc:$PATH
fi

The braces are required for concatenation constructs.

$p_01

The value of the variable "p_01".

${p}_01

The value of the variable "p" with "_01" pasted onto the end.

o Conditional Reference

${variable-word}

If the variable has been set, use it's value, else use word.

POSTSCRIPT=${POSTSCRIPT-PostScript};
export POSTSCRIPT

${variable:-word}

If the variable has been set and is not null, use it's value, else use word.

These are useful constructions for honoring the user envi- ronment. Ie. the user of the script can override variable assignments. Cf. programs like lpr(1) honor the PRINTER environment variable, you can do the same trick with your shell scripts.

${variable:?word}

If variable is set use it's value, else print out word and exit. Useful for bailing out.

o Arguments

Command line arguments to shell scripts are positional vari- ables:

$0, $1, ...

The command and arguments. With $0 the command and the rest the arguments.

$#

The number of arguments.

$*, $@

All the arguments as a blank separated string. Watch out for "$*" vs. "$@".
And, some commands:

shift

Shift the postional variables down one and decrement number of arguments.

set arg arg ...

Set the positional variables to the argument list.

Command line parsing uses shift:

# parse argument list

while [ $# -ge 1 ]; do
case $1 in
process arguments...
esac
shift
done

A use of the set command:

# figure out what day it is

TODAY=`(set \`date\`; echo $1)`

cd $SPOOL

for i in `cat $LOGS`
do
mv $i $i.$TODAY
cp /dev/null $i
chmod 664 $i
done

o Special Variables

$$

Current process id. This is very useful for constructing temporary files.

tmp=/tmp/cal0$$
trap "rm -f $tmp /tmp/cal1$$ /tmp/cal2$$"
trap exit 1 2 13 15
/usr/lib/calprog >$tmp

$?

The exit status of the last command.

$command
# Run target file if no errors and ...

if [ $? -eq 0 ]
then
etc...
fi


* Quotes/Special Characters

Special characters to terminate words:

; & ( ) | ^ < > new-line space tab

These are for command sequences, background jobs, etc. To quote any of these use a backslash (\) or bracket with quote marks ("" or '').

Single Quotes

Within single quotes all characters are quoted -- including the backslash. The result is one word.

grep :${gid}: /etc/group | awk -F: '{print $1}'

Double Quotes

Within double quotes you have variable subsitution (ie. the dollar sign is interpreted) but no file name generation (ie. * and ? are quoted). The result is one word.

if [ ! "${parent}" ]; then
parent=${people}/${group}/${user}
fi

Back Quotes

Back quotes mean run the command and substitute the output.

if [ "`echo -n`" = "-n" ]; then
n=""
c="\c"
else
n="-n"
c=""
fi

and

TODAY=`(set \`date\`; echo $1)`

* Functions

Functions are a powerful feature that aren't used often enough. Syntax is

name ()
{
commands
}

For example:

# Purge a directory

_purge()
{
# there had better be a directory

if [ ! -d $1 ]; then
echo $1: No such directory 1>&2
return
fi

etc...
}

Within a function the positional parmeters $0, $1, etc. are the arguments to the function (not the arguments to the script).

Within a function use return instead of exit.

Functions are good for encapsulations. You can pipe, redi- rect input, etc. to functions. For example:

# deal with a file, add people one at a time

do_file()
{
while parse_one

etc...
}

etc...

# take standard input (or a specified file) and do it.

if [ "$1" != "" ]; then
cat $1 | do_file
else
do_file
fi

* Sourcing commands

You can execute shell scripts from within shell scripts. A couple of choices:

sh command

This runs the shell script as a separate shell. For example, on Sun machines in /etc/rc:

sh /etc/rc.local

. command

This runs the shell script from within the current shell script. For example:

# Read in configuration information
. /etc/hostconfig

What are the virtues of each? What's the difference? The second form is useful for configuration files where environment variable are set for the script. For example:

for HOST in $HOSTS; do

# is there a config file for this host?

if [ -r ${BACKUPHOME}/${HOST} ]; then
. ${BACKUPHOME}/${HOST}
fi
etc...

Using configuration files in this manner makes it possible to write scripts that are automatically tailored for differ- ent situations.

Some Tricks

* Test

The most powerful command is test(1).

if test expression; then

etc...

and (note the matching bracket argument)

if [ expression ]; then

etc...

On System V machines this is a builtin (check out the com- mand /bin/test).

On BSD systems (like the Suns) compare the command /usr/bin/test with /usr/bin/[.

Useful expressions are:

test { -w, -r, -x, -s, ... } filename

is file writeable, readable, executeable, empty, etc?

test n1 { -eq, -ne, -gt, ... } n2

are numbers equal, not equal, greater than, etc.?

test s1 { =, != } s2

Are strings the same or different?

test cond1 { -o, -a } cond2

Binary or; binary and; use ! for unary negation.

For example

if [ $year -lt 1901 -o $year -gt 2099 ]; then
echo 1>&2 Year \"$year\" out of range
exit 127
fi

Learn this command inside out! It does a lot for you.

* String matching

The test command provides limited string matching tests. A more powerful trick is to match strings with the case switch.

# parse argument list

while [ $# -ge 1 ]; do
case $1 in
-c*) rate=`echo $1 | cut -c3-`;;
-c) shift; rate=$1 ;;
-p*) prefix=`echo $1 | cut -c3-`;;
-p) shift; prefix=$1 ;;
-*) echo $Usage; exit 1 ;;
*) disks=$*; break ;;
esac

shift

done

Of course getopt would work much better.

* SysV vs BSD echo

On BSD systems to get a prompt you'd say:

echo -n Ok to procede?; read ans

On SysV systems you'd say:

echo Ok to procede? \c; read ans

In an effort to produce portable code we've been using:

# figure out what kind of echo to use

if [ "`echo -n`" = "-n" ]; then
n=""; c="\c"
else
n="-n"; c=""
fi

etc...

echo $n Ok to procede? $c; read ans

* Is there a person?

The Unix tradition is that programs should execute as qui- etly as possible. Especially for pipelines, cron jobs, etc.

User prompts aren't required if there's no user.

# If there's a person out there, prod him a bit.

if tty -s; then
echo Enter text end with \^D
fi

The tradition also extends to output.

# If the output is to a terminal, be verbose

if tty -s <&1; then
verbose=true
else
verbose=false
fi

Beware: just because stdin is a tty that doesn't mean that stdout is too. User prompts should be directed to the user terminal.

# If there's a person out there, prod him a bit.

if tty -s; then
echo Enter text end with \^D >&0
fi

Have you ever had a program stop waiting for keyboard input when the output is directed elsewhere?

* Creating Input

We're familiar with redirecting input. For example:

# take standard input (or a specified file) and do it.

if [ "$1" != "" ]; then
cat $1 | do_file
else
do_file
fi

alternatively, redirection from a file:

# take standard input (or a specified file) and do it.

if [ "$1" != "" ]; then
do_file < $1
else
do_file
fi

You can also construct files on the fly.

rmail bsmtp <<$1@newshost.uwo.ca>
rcpt to:
data
from: <$1@newshost.uwo.ca>
to:
Subject: Signon $2

subscribe $2 Usenet Feeder at UWO
.
quit
EOF

Note: that variables are expanded in the input.

* String Manipulations

One of the more common things you'll need to do is parse strings. Some tricks

TIME=`date | cut -c12-19`

TIME=`date | sed 's/.* .* .* \(.*\) .* .*/\1/'`

TIME=`date | awk '{print $4}'`

TIME=`set \`date\`; echo $4`

TIME=`date | (read u v w x y z; echo $x)`

With some care, redefining the input field separators can help.

#!/bin/sh
# convert IP number to in-addr.arpa name

name()
{ set `IFS=".";echo $1`
echo $4.$3.$2.$1.in-addr.arpa
}

if [ $# -ne 1 ]; then
echo 1>&2 Usage: bynum IP-address
exit 127
fi

add=`name $1`

nslookup < < EOF | grep "$add" | sed 's/.*= //'
set type=any
$add
EOF

* Debugging

The shell has a number of flags that make debugging easier:

sh -n command

Read the shell script but don't execute the commands. IE. check syntax.

sh -x command

Display commands and arguments as they're executed. In a lot of my shell scripts you'll see

# Uncomment the next line for testing
# set -x

Based on An Introduction to Shell Programing by:
Reg Quinton
Computing and Communications Services
The University of Western Ontario
London, Ontario N6A 5B7
Canada

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