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Shell Programming and Scripting

Testing for EOF during a while loop

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Top Forums Shell Programming and Scripting Testing for EOF during a while loop
# 8  
Old 10-07-2010
This command should tell you what Operating System you have on any unix or Linux platfrom:
Code:
uname -a


And the Shell (works on most modern platforms):
Code:
echo ${SHELL}

Last edited by methyl; 10-07-2010 at 11:11 PM.. Reason: layout
# 9  
Old 11-14-2010
Hi,

I am new to shell scripting, and I was trying the same thing where I want to read whether I have entered more than one line or not,
i.e. I have a command called grader
Code:
grader "add1
> add2"

shoudl give me a reply of 1, but it gives me output of 0

but If I write
Code:
grader
>add1
>add2

and then Ctrl + d it gives me output of "2"

please let me know what can be done if I want to even count within quotes that it is a name with new line in it.

I have used the same code as posted here
Code:
#!/bin/bash

i=0
while read ans
do 
  i=$(( i+1 ))
done
echo $i

Moderator's Comments:
Mod Comment In future, please start a new thread instead of hijacking someone else's. Thanks
Last edited by Scott; 11-14-2010 at 12:46 PM.. Reason: Please use code tags
# 10  
Old 11-14-2010
The code you have is designed to prompt and accept lines on standard input. The first example you give (the one with the quotes) is passing parameters to the program not input. The following should be used instead:

Code:
$ echo "add1
> add2" | grader
2

# 11  
Old 11-14-2010
If you make a small adjustment to your script then it should be able to read the input on the command line.
Code:
#!/bin/bash
exec 3<&0
if [ $# -gt 0 ]; then
  exec 0<<<"$@"
fi
i=0
while read ans
do
  i=$(( i+1 ))
done
echo $i
exec 0<&3

Code:
$ ./grader "add1
add2"
2

Last edited by Scrutinizer; 11-14-2010 at 02:00 PM.. Reason: added exec and put exec 3<&0 before if...
This User Gave Thanks to Scrutinizer For This Post:
life_is_good
# 12  
Old 11-14-2010
Code:
#!/usr/bin/ksh
while read ans?"Enter something:"
do
if [[ -n $ans ]]; then let i++
else break
fi
done
echo "\nYou answered $i times"

Last edited by ctsgnb; 11-14-2010 at 12:31 PM..
This User Gave Thanks to ctsgnb For This Post:
life_is_good
# 13  
Old 11-14-2010
---------- Post updated at 11:41 AM ---------- Previous update was at 11:39 AM ----------

Quote:
Originally Posted by Scrutinizer
If you make a small adjustment to your script then it should be able to read the input on the command line.
Code:
#!/bin/bash
if [ $# -gt 0 ]; then
  exec 3<&0 0<<<"$@"
fi
i=0
while read ans
do
  i=$(( i+1 ))
done
echo $i
0<&3

Code:
$ ./grader "add1
add2"
2


Thank you Scrutinizer that worked!!

though, I did not understand what does this do?
Code:
exec 3<&0 0<<<"$@"

with <<< are you trying to shift?

and why did you use
Code:
0<&3

in the end? even if I don't have it, also then it works.

Thanks!!
Last edited by Scott; 11-14-2010 at 12:47 PM.. Reason: Code tags
# 14  
Old 11-14-2010
<<< is a so-called here-string, which is a ksh93/bash construct. It redirects stdin from a string.

Regarding 0<&3 you could have used:
Code:
#!/bin/bash
if [ $# -gt 0 ]; then
  0<<<"$@"
fi
i=0
while read ans
do
  i=$(( i+1 ))
done
echo $i

But then stdin would be no longer usable later on in your script. That is why I used file descriptor 3 to save where stdin was reading from and I redirected stdin to its old value at the end..
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