problem in writing a script?

sonu kumar · 02-08-2010, 07:24 AM

hi dear all,

i have written a script in which, i changes a variable using a "while" loop. then i feed that variable to an input file. After that i run that file in parallal using mpi library.Script is as:>>>>

#!/bin/bash

STA=/home/sk/Desktop/exefile

sta=mpirun -np 6 $STA

# where -np is no. of processors,i took them=6

ES=30

while [ $ES -le 200 ]

do

echo "$ES" >> sourcefile
$sta< sourcefile > $ES.out
let ES=$ES+10

done

when i run the script .
i got the following error:
./variable.sh: line 5: -np: command not found.

how can i solve this problem?

with regards

skumar

catkin · 02-08-2010, 07:33 AM

To assign the entire string mpirun -np 6 $STA to a variable you need to enclose it in quotes. In this case, where it includes a variable for which you want to substitute its value, you need double quotes

Code:

sta="mpirun -np 6 $STA"

The original command (statement) told bash to assign string mpirun to variable $sta and, with that assignment in effect, run command -np 6 $STA.

colucix · 02-08-2010, 07:33 AM

Code:

sta=mpirun -np 6 $STA

Here, to assign a string containing spaces to a variable, you have to use double quotes. Without them, the shell sets the variable sta to "mpirun" and tries to execute the rest as a command.

Edit: ...as catkin said just a bunch of seconds ago...

JimBrewster · 02-08-2010, 07:38 AM

You need to quote the sta variable:

Code:

sta="mpirun -np 6 $STA"

sonu kumar · 02-08-2010, 07:57 AM

Quote:

Originally Posted by colucix

Code:

sta=mpirun -np 6 $STA

Here, to assign a string containing spaces to a variable, you have to use double quotes. Without them, the shell sets the variable sta to "mpirun" and tries to execute the rest as a command.

Edit: ...as catkin said just a bunch of seconds ago...

!! thank you very much to all of you !!

can you, please, tell/suggest me the materail/stuff required to write a script in linux. I have just started. i found many sites for shell scripting, but i don't understand them easily/completely.

With warm regards

skumar

chrism01 · 02-08-2010, 05:05 PM

3 very good tutorials; read them and TRY stuff if you don't understand it. Nobody can magically make you a bash guru instantly.

http://rute.2038bug.com/index.html.gz
http://tldp.org/LDP/Bash-Beginners-G...tml/index.html
http://www.tldp.org/LDP/abs/html/

catkin · 02-08-2010, 10:51 PM

Quote:

Originally Posted by chrism01

Nobody can magically make you a bash guru instantly.

Truly. Like all languages (maybe more than some), fluency comes from practising, practising, practising ... and asking for advice when you get stuck

sonu kumar · 02-09-2010, 03:36 AM

Quote:

Originally Posted by catkin

Truly. Like all languages (maybe more than some), fluency comes from practising, practising, practising ... and asking for advice when you get stuck

Thank you very much!!!

I find that in bash script, loops like while loop doesn't take fractional increment.
is there any remedy for it?

with Regards
skumar

catkin · 02-09-2010, 04:00 AM

Quote:

Originally Posted by sonu kumar

I find that in bash script, loops like while loop doesn't take fractional increment.
is there any remedy for it?

Can you post what you have tried? Bash only handles integers but there will be a way to do what you want to do.

sonu kumar · 02-09-2010, 04:41 AM

Quote:

Originally Posted by catkin

Can you post what you have tried? Bash only handles integers but there will be a way to do what you want to do.

hi catkin and all linux users!!

i tried to increment a fractional variable by fractions.

Script is:

#!/bin/bash

echo "if u want 2 use fractional while loop, enter 8"
read what
if [ $what=8 ]; then
SN=0.10
# echo "1/5" | bc -l
while [ $SN -le 0.20 ]; do
echo "your no. is is $SN"
echo "Char is $SN" >> lab.f
let SN=$SN+0.1
done
else
echo "ok, right "
fi

error is:
if u want 2 use fractional while loop, enter 8
8
./sp.sh: line 8: [: 0.10: integer expression expected

if u want 2 use fractional while loop, enter 8
2
./sp.sh: line 8: [: 0.10: integer expression expected

Also it doesn't matter whether i enter 8 or any other number, i didn't get ok, right.

regards
skumar

jschiwal · 02-09-2010, 04:55 AM

Either use integers to control your loop and divide in "bc" to provide feedback to the user, or move the test inside bc.

bc does have comparison tests, print, read and while. The entire loop could be in bc but only because the loop doesn't really do anything.

You really need to avoid using floating point values to control loops. Even in languages that have floats, conversion errors between a floating point value and its internal representation can cause problems. E.G. don't compare two floating point values for equality. The result might be due to a conversion error.

Also for integer arithmetic, use [[ ... ]] in tests instead of [ ... ].

sonu kumar · 02-09-2010, 05:37 AM

[QUOTE=jschiwal;3857658]Either use integers to control your loop and divide in "bc" to provide feedback to the user, or move the test inside bc.

hi dear all !

how can i use "bc" in this context?

also echo "if u want 2 use fractional while loop, enter 8"
read what is not working properly.
skumar

catkin · 02-09-2010, 05:54 AM

[QUOTE=sonu kumar;3857674]

Quote:

Originally Posted by jread what[/COLOR

is not working properly.

Read what is probably working OK but testing it is not. Try

Code:

if [[ $what = 8 ]]

chrism01 · 02-09-2010, 05:22 PM

For numeric comparisons, that should be '-eq' not '=' http://www.tldp.org/LDP/abs/html/com...l#ICOMPARISON1.
I agree that [[ ]] is better than [ ] http://www.tldp.org/LDP/abs/html/tes...ml#DBLBRACKETS

Also, whilst assignments require no spaces around the operator ie

X=B

comparisons require a min of one space on each side of the operator (and the brackets) eg

if [[ $a -eq $b ]]

jschiwal · 02-10-2010, 05:33 AM

Code:

jschiwal@qosmio:~/work> cat bcex                                  
#!/usr/bin/env bc                                                 
scale=2                                                           
sn=0.10                                                           
print "enter value: "                                             
value=read()                                                      
while ( value <= 0.2 ){
  print "Your no. is ", value, "\n"
  value+=0.1
}
print "ok,right\n"
quit

jschiwal@qosmio:~/work> ./bcex
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
enter value: 0.01
Your no. is .01
Your no. is .11
ok,right
jschiwal@qosmio:~/work>

Here is your example in bc instead of bash.
You could have lines like:
echo "scale=2; $value <= 10.5" | bc
and then test for a result of "0" or "1".

You could hide the use of bc in your bash program by using bc in functions.

Here is an example using sed in a function to keep just the integer part of a string. You can assign the result to an integer variable:
intpart(){ local value result; value="${1}"; result=$(echo "$value" | sed 's/[^[:digit:]].*//'); echo $result ;}
You could modify it to use bc to round of the value first.