read command in shell script what to do for reading a particular char

Ashok_mittal · 01-17-2008, 03:05 AM

What is the shell command like read to read a particular char from input
like if i want c to be entered to go forward and execute another shell commands.

sophkos · 01-17-2008, 03:21 AM

If you want c to be entered you type: read c

amitsurana · 01-17-2008, 03:34 AM

read Value
if(($value=="c"))
then
echo "move forward"
fi

m not sure of scripting syntax here
but using "read <variable-name>" will read the standard input into <variable-name>.

Ashok_mittal · 01-17-2008, 04:43 AM

Quote:

Originally Posted by amitsurana

read Value
if(($value=="c"))
then
echo "move forward"
fi

m not sure of scripting syntax here
but using "read <variable-name>" will read the standard input into <variable-name>.

I have written the code as

date
read value1
if [ $value1="acd" ]
then
who
fi
exit

now it should print only the date and exit but instead it is printing date and then executing who command.
so what should be the testing conditions in if [..] to compare with value1
and then decide whether to execute who or not.

amitsurana · 01-17-2008, 11:38 PM

Quote:

Originally Posted by Ashok_mittal

I have written the code as

date
read value1
if [ $value1="acd" ]
then
who
fi
exit

now it should print only the date and exit but instead it is printing date and then executing who command.
so what should be the testing conditions in if [..] to compare with value1
and then decide whether to execute who or not.

the IF statement synatax is :
if[$value -eq <your-string>]
then
<statements>
fi
<more - statements>

chrism01 · 01-18-2008, 12:38 AM

Actully, it's

Code:

if [[ $val = "test_str" ]]
then
    <do stuff>
else
    <do other>
fi

note the spaces around the double '[[' ']]' and also note that you use '=', '<' etc for string comparisons and -eq etc for numeric comparisons: http://www.tldp.org/LDP/abs/html/comparison-ops.html

Ashok_mittal · 01-18-2008, 12:46 AM

Quote:

Originally Posted by chrism01

Actully, it's

Code:

if [[ $val = "test_str" ]]
then
    <do stuff>
else
    <do other>
fi

note the spaces around the double '[[' ']]' and also note that you use '=', '<' etc for string comparisons and -eq etc for numeric comparisons: http://www.tldp.org/LDP/abs/html/comparison-ops.html

it is still executing 'who' command in if condition no matter the condition is true or false.

anupamsr · 01-18-2008, 05:48 AM

this script works perfectly fine on my computer:

Code:

#!/bin/bash

read value
if [[ "$value" == "anda" ]]; then
	echo "You entered anda"
else
	echo "You didn't entered anda, instead you entred $value"
fi

Ashok_mittal · 01-21-2008, 02:40 AM

Quote:

Originally Posted by anupamsr

this script works perfectly fine on my computer:

Code:

#!/bin/bash

read value
if [[ "$value" == "anda" ]]; then
	echo "You entered anda"
else
	echo "You didn't entered anda, instead you entred $value"
fi

Thanks for your valuable help but it won't work unless there are spaces b/w
"$value" and '==' & '==' and "anda"
for the expected comparison "$value"="anda" the condition must be like this.

anupamsr · 01-21-2008, 03:29 AM

Of course it won't work if you don't have spaces between them. That is why there are spaces between them. I don't understand what you mean.

Ashok_mittal · 01-21-2008, 03:39 AM

Quote:

Originally Posted by anupamsr

Of course it won't work if you don't have spaces between them. That is why there are spaces between them. I don't understand what you mean.

Yes you are absolutely right but can u get me understood why the gcc compiler making the condition always true when there are no spaces whether the strings are same or different . Like

read value1
echo "value is $value1"
if [[ "$value1"=="acd" ]];
then
pwd
else
who
fi

It is executing command 'pwd' in any case.

colucix · 01-21-2008, 05:01 AM

If you don't put spaces around the = or == signs, the shell will not interpret it as a comparison:

Code:

[[ string == string ]]

but as a single random string:

Code:

[[ string ]]

and a random string always evaluates as TRUE. See The Advanced Bash Scripting Guide, Section 7.1 for more details.