Scripting query..

crash_override_me · 07-22-2007, 10:59 AM

hi..

can anyone tell me wats wrong in this script..? & how do i correct it..?

Code:

# matches pattern

a=$1

for i in a..z
do
 if [ $a == i* ]
 then
   echo "String starts with" $i
 fi
done

wjevans_7d1@yahoo.co · 07-22-2007, 11:49 AM

Don't keep it a secret. What is this script doing for you, and what do you want it to do differently?

Guitarist88 · 07-22-2007, 12:07 PM

Ok well I haven't done bash in a very long time and I've been concentrating on c++ for school lately but I'll try to help you a bit. I'm sure some more experienced person will come a long and finish what I've started or correct me. I'll do my best.

Ok I gather you are taking in the first parameter sent with the script and seeing what lowercase letter its starts with.

To test string equality you have to use a single equals sign with the test command. Try man test to see all the different operators.

And you forgot that derefernce $ sign thing in front of the i. The only thing I'm not quite sure of is how the * wildcard works next to a string like that. I don't have Bash in front of me to test as I'm residing in the forbidden land right now...

so in the end it will look something like this:

Code:

# matches pattern

a=$1

for i in a..z
do
 if [ $a = $i* ]
 then
   echo "String starts with" $i
 fi
done

I hope that helps.

radoulov · 07-22-2007, 12:13 PM

Quote:

Originally Posted by crash_override_me

hi..

can anyone tell me wats wrong in this script..? & how do i correct it..?

Code:

# matches pattern

a=$1

for i in a..z
do
 if [ $a == i* ]
 then
   echo "String starts with" $i
 fi
done

Code:

a="$1"

for i in {a..z}
do
 if [[ "$a" == "$i"* ]]
 then
   echo "String starts with $i"
 fi
done

You can write it just as (assuming bash) to match any character:

Code:

echo "String starts with "${1%${1#?}}"

crash_override_me · 07-22-2007, 01:54 PM

Quote:

Originally Posted by radoulov

Code:

a="$1"

for i in {a..z}
do
 if [[ "$a" == "$i"* ]]
 then
   echo "String starts with $i"
 fi
done

You can write it just as (assuming bash) to match any character:

Code:

echo "String starts with "${1%${1#?}}"

thanx for the help..!

i have 2 questions:

1. why r we using double [[ .. ]]
2. what exactly is the second script doing..?

radoulov · 07-22-2007, 02:25 PM

Quote:

Originally Posted by crash_override_me

thanx for the help..!

i have 2 questions:

1. why r we using double [[ .. ]]

Because you cannot use wild cards (*) with
the test operator ([):

Code:

radoulov@ubuntu:~$ [ "ab" = "a"* ]&& echo OK||echo KO
KO
radoulov@ubuntu:~$ [[ "ab" = "a"* ]]&& echo OK||echo KO
OK

But the [[ ... ]] construct is not standard (as far as I know).

Quote:

2. what exactly is the second script doing..?

It just prints the first character of
the first argument ($1):

Code:

radoulov@ubuntu:~$ set -- abc;echo "${1%${1#?}}"
a

With bash you can write it also as:

Code:

radoulov@ubuntu:~$ set -- abc;echo "${1:0:1}"
a

With zsh:

Code:

ubuntu% set -- abc;echo "${1[1]}"
a

You can also use printf to substring:

Code:

ubuntu% set -- abc;printf "%.1s\n" "$1"
a

crash_override_me · 07-23-2007, 02:45 AM

Quote:

Originally Posted by radoulov

With bash you can write it also as:

Code:

radoulov@ubuntu:~$ set -- abc;echo "${1:0:1}"
a

what does 1:0:1 does..??

crash_override_me · 07-23-2007, 02:51 AM

something is wrong wid the code below..
error:
line 7: [: : integer expression expected
line 10: [: : integer expression expected
line 13: [: : integer expression expected
line 16: [: : integer expression expected

Code:

# says good mrng, eve, afternoon, or night depending on time.

x=`date|awk '{ print $4 }'|awk -F:'{ print $1 }'`

if [ "$x" -lt 4 ]
then
  echo "good night"
elif [ "$x" -lt 12 ]
then
  echo "good morning"
elif [ "$x" -lt 16 ]
then
  echo "good afternoon"
elif [ "$x" -lt 20 ]
then
  echo "good evening"
fi

ghostdog74 · 07-23-2007, 04:20 AM

Quote:

Originally Posted by crash_override_me

Code:

x=`date|awk '{ print $4 }'|awk -F:'{ print $1 }'`

that's because you don't have a space in between -F: and '{print $1}'
There is also no need for double awk calls:

Code:

date|awk '{ n=split($4,d,":")
            if ( d[1] < 4 ){ print "Good night" }
	    if ( d[1] < 12 ) { print "Good morning" }
	    if ( d[1] < 16 ) { print "Good Afternoon" }
	    if ( d[1] < 20 ) { print "Good evening" }   
	
}'

or just use

Code:

hr=$(date +%H)
if [ $hr -lt 4 ]
....
...
fi