[Scripting] Strings

IPAddress · 09-02-2009, 09:55 AM

Hi.
Im running a CentOS release 5.3 (Final) and im triyng to make a script to compare two lines of two files...

My Script:

Code:

#! /bin/bash

# CREATE ONE OF THE FILES: LIST OF ALL DOMAINS IN MY DNS SERVER.
cd /var/named/data
declare -a dominios=( * )

# CLEAN THE OTHER FILE FOR THE LAST CHARACTER.
#rev /var/www/html/ipaddress/lista | cut -b 2- | rev >> /var/www/html/ipaddress/dominios.txt

CantDominios=`sed -n '$=' /var/www/html/ipaddress/dominios.txt`
existe=false


for (( j = 1 ; j < $CantDominios ; j++ )) do
    Dominio=`head -n $j /var/www/html/ipaddress/dominios.txt | tail -n 1`
    for (( i = 0 ; i < ${#dominios[@]} ; i++ )) do
         [ ${dominios[$i]} == $Dominio ];${existe:=true}
         echo $existe "[${dominios[$i]}/$Dominio]"
    done
    if ($existe == false ) then
        echo ''  >> /etc/named.conf.BK
        echo 'zone "'$Dominio'" {' >> /etc/named.conf.BK
        echo '       type slave;' >> /etc/named.conf.BK
        echo '           file "/var/named/data/'$Dominio'";' >> /etc/named.conf.BK
        echo ''          >> /etc/named.conf.BK
        echo ''          >> /etc/named.conf.BK
        echo '            masters {xxx.yyy.www.zzz;' >> /etc/named.conf.BK
        echo '            };' >> /etc/named.conf.BK
        echo '};' >> /etc/named.conf.BK
    fi
        ${existe:=false};
done

# REMOVE THE FILE
#rm -f /var/www/html/ipaddress/dominios.txt

However theres a problem, cause "Existe" is always "false", even when the lines are exactly the same!
Maybe its because the way i'm comparing the string i take from ${dominios[$i]} and the string i take from $Dominio.
Any ideas?

Thanks in advance.

Bye!

catkin · 09-02-2009, 12:50 PM

This line is strange

Code:

[ ${dominios[$i]} == $Dominio ];${existe:=true}

Should it be

Code:

[ ${dominios[$i]} == $Dominio ] && existe=true

If so, it would be more robustly coded as

Code:

[[ "${dominios[$i]}" == "$Dominio" ]] && existe=true

IPAddress · 09-02-2009, 01:12 PM

Quote:

Originally Posted by catkin

This line is strange

Code:

[ ${dominios[$i]} == $Dominio ];${existe:=true}

Should it be

Code:

[ ${dominios[$i]} == $Dominio ] && existe=true

If so, it would be more robustly coded as

Code:

[[ "${dominios[$i]}" == "$Dominio" ]] && existe=true

Hi.
I think you meant...

Code:

[[ "${dominios[$i]}" == "$Dominio" ]] && $existe=true

But with that i get the output...
line 15: false=true: command not found
Is that the only change i have to do?

The idea of that line is to check...
if dominios[i] = Dominio then, i want existe to be true. An then, every time the i check " if ($existe == false )" to put $existe==true

Any ideas?

Bye!

anomie · 09-02-2009, 01:23 PM

Eh.. you want to assign a value to the existe variable, right? Then don't expand ($) it. i.e.:

Code:

existe="true"

That's another thing -- you should probably be quoting string values. That helps when you're doing logical comparisons, so if you bump into an unset / no-value variable you won't get a syntactical error.

IPAddress · 09-03-2009, 12:11 PM

Quote:

Originally Posted by anomie

Eh.. you want to assign a value to the existe variable, right? Then don't expand ($) it. i.e.:

Code:

existe="true"

That's another thing -- you should probably be quoting string values. That helps when you're doing logical comparisons, so if you bump into an unset / no-value variable you won't get a syntactical error.

Well, i'm finishing the script, but theres still one problem. Now the script is this:

Code:

# cat /root/ReplicarDns.sh
#! /bin/bash

grep -v ".in-addr.arpa" list.txt >> lista
chmod 777 /var/www/html/ipaddress/lista
rm -f list.txt
cd /var/named/data
declare -a dominios=( * )
rev /var/www/html/ipaddress/lista | cut -b 2- | rev >> /var/www/html/ipaddress/dominios.txt
rm -f /var/www/html/ipaddress/lista
CantDominios=`sed -n '$=' /var/www/html/ipaddress/dominios.txt`
existe="false"
Eliminar="logging {category lame-servers { null; };};"
(echo "g/${Eliminar}/d"; echo 'wq') | ex -s /etc/named.conf.BK
for (( j = 1 ; j <= $CantDominios ; j++ )) do
    Dominio=`head -n $j /var/www/html/ipaddress/dominios.txt | tail -n 1`
    for (( i = 0 ; i < ${#dominios[@]} ; i++ )) do
        [ ${dominios[$i]} == $Dominio ] && existe="true"
    done
    if ( $existe=="false" ) then
    echo 'The Domain ' "$Dominio" ' exist? ' $existe
        echo ''  >> /etc/named.conf.BK
        echo 'zone "'$Dominio'" {' >> /etc/named.conf.BK
        echo '       type slave;' >> /etc/named.conf.BK
        echo '           file "/var/named/data/'$Dominio'";' >> /etc/named.conf.BK
        echo ''          >> /etc/named.conf.BK
        echo ''          >> /etc/named.conf.BK
        echo '            masters {xxx.yyy.www.zzz;' >> /etc/named.conf.BK
        echo '            };' >> /etc/named.conf.BK
        echo '};' >> /etc/named.conf.BK
    fi
    existe="false";
done
echo '' >> /etc/named.conf.BK
echo 'logging {category lame-servers { null; };};' >> /etc/named.conf.BK
 rm -f /var/www/html/ipaddress/dominios.txt
#/etc/init.d/named restart

But for some reason its allways entering in the if:

Code:

if ( $existe=="false" ) then

Why?

Thanks.

Bye!

catkin · 09-03-2009, 12:23 PM

Because ( <test expression> ) simply runs the test expression in a sub-shell where it is interpreted as a command (so should generate "bash: true==false: command not found"; did you not see that?).

Test expressions need to appear in one of the three test formats, the best of which is [[ <test expression> ]]

anomie · 09-03-2009, 01:52 PM

Quote:

Originally Posted by IPAddress

Code:

if ( $existe=="false" ) then

And to add to the previous comment, you're missing a semicolon as well.

Code:

if [ "${existe}" == "false" ] ; then

gnashley · 09-03-2009, 01:53 PM

This:
if ( $existe=="false" ) then
should be this:
if [[ "$existe" = "false" ]] ; then

anomie · 09-03-2009, 02:30 PM

@catkin & @gnashley: I'm curious why you recommend the extended test command - [[ ... ]] - in this case instead.

Code:

$ _foo='barbazboo'
$ if [ "${_foo}" == "barbazboo" ] ; then echo 'OK!' ; fi
OK!
$ unset _foo
$ if [ "${_foo}" == "barbazboo" ] ; then echo 'OK!' ; fi

anomie · 09-03-2009, 02:35 PM

Also, not to nitpick too much (and pollute poor OP's thread), but I dislike using -

Code:

- as a comparison operator. I know it's syntactically (and logically) legit with bash, but it sends off alarm bells in my mind because it looks like strictly an assignment operator in many other languages.

catkin · 09-03-2009, 03:24 PM

[[ ]] was introduced to the shell after [ ] to compensate for some of its deficiencies. See http://tldp.org/LDP/abs/html/testconstructs.html and search for "The [[ ]] construct is the more versatile Bash version of [ ]".

anomie · 09-03-2009, 03:26 PM

That's what I linked to in my post. I was curious why you recommended it in this particular case.

chrism01 · 09-04-2009, 12:46 AM

http://tldp.org/LDP/abs/html/testcon...ml#DBLBRACKETS is just generally more robust

"Using the [[ ... ]] test construct, rather than [ ... ] can prevent many logic errors in scripts. For example, the &&, ||, <, and > operators work within a [[ ]] test, despite giving an error within a [ ] construct.
"

plus I read somewhere it copes better/correctly with unassigned/empty args.
Basically, I was told on my (ksh) course many yrs ago the whys & wherefores of the various options to 'check' something, and told to stick to it ie [[ ]].
Personally I always do. Its basically the 'best' (see prev remarks) and it's easier than trying to remember the different limitations of 'test' vs bare 'if' vs [ ] vs [[ ]].
YMMV

catkin · 09-04-2009, 01:19 AM

Quote:

Originally Posted by anomie

That's what I linked to in my post. I was curious why you recommended it in this particular case.

I am sorry I didn't notice the link. For the reasons mentioned by chrism01, I recommend it in all cases.

anomie · 09-04-2009, 11:17 AM

Thanks for the musings, guys. I'll think this through some more. On a normal week I whip together a half dozen bash scripts to automate things; I try to stay with a set of best practices to make life easer.

It does bother me that [[ ... ]] is getting away from Bourne shell compatibility. But the reality is I'm working on 90% Linux hosts these days anyway, where bash is default.

-------

@IPAddress: sorry to digress on your thread. I hope your question was answered.