while ...loop

flaskvacuum · 01-06-2013, 10:06 PM

Code:

total=1
c=1
test_1=ready1
test_2=ready2
test_3=ready3

while [ c -le total ]
do
	DUMP_DIR=/home/john/admin/$SID_$c/dump
	
	echo "$DUMP_DIR"

	c=`expr $c + 1`
	echo "$c"
done

hi i have trouble interpreting the loops
#SID_$c

how can i escape the "_"
i just need to loop through:
test_1
test_2
test_3

which the number is incremented by $c

smallpond · 01-06-2013, 10:21 PM

I see three mistakes:

1) You haven't defined SID. Looks like you want

Code:

SID=test

2) Your while condition is wrong. It needs to be:

Code:

while [ $c -le $total ]

3) When a variable is part of a word it needs to be in brackets:

Code:

        DUMP_DIR=/home/john/admin/${SID}_${c}/dump

shivaa · 01-06-2013, 10:23 PM

You could have used array after initializing total to 2 and c to 0:

Code:

#!/bin/bash
total=2
c=0
arr=(ready1 ready2 ready3)
while [ $c -le $total ]
do
	DUMP_DIR=/home/john/admin/${arr[$c]}/dump
	echo "$DUMP_DIR"
	c=`expr $c + 1`
	echo "$c"
done

flaskvacuum · 01-07-2013, 12:01 AM

total=1
c=1
test_1=ready1
test_2=ready2
test_3=ready3

while [ c -le total ]
do
DUMP_DIR=$SID_$c

echo "$DUMP_DIR"

c=`expr $c + 1`
echo "$c"
done

erm, is not printing the value of the variable
It should print the value of the variable test_1 -> ready1 ..etc

shivaa · 01-07-2013, 12:38 AM

Check my post above (which I edited and saved mistakenly, sorry for that):
Use a simple array in that case, as:

Code:

#!/bin/bash
total=2
c=0
arr=(ready1 ready2 ready3)
while [ $c -le $total ]
do
	DUMP_DIR=/home/john/admin/${arr[$c]}/dump
	echo "$DUMP_DIR"
	c=`expr $c + 1`
	echo "$c"
done

flaskvacuum · 01-07-2013, 12:51 AM

Quote:

Originally Posted by shivaa

Check my post above (which I edited and saved mistakenly, sorry for that):
Use a simple array in that case, as:

Code:

#!/bin/bash
total=2
c=0
arr=(ready1 ready2 ready3)
while [ $c -le total ]
do
	DUMP_DIR=/home/john/admin/${arr[$c]}/dump
	echo "$DUMP_DIR"
	c=`expr $c + 1`
	echo "$c"
done

i have change

Code:

#!/bin/bash
total=2
c=0
arr=(ready1 ready2 ready3)
while [ $c -le total ]
do
	DUMP_DIR=${arr[$c]}
	echo "$DUMP_DIR"
	c=`expr $c + 1`
	#echo "$c"
done

but with the error.

Syntax error at line 6 : `(' is not expected.

shivaa · 01-07-2013, 01:07 AM

Code:

DUMP_DIR=${arr[$c]}
	echo "$DUMP_DIR"

What is need to first saving the array element in DUMP_DIR and then printing DUMP_DIR? Instead, you can directly print array element, as:-

Code:

echo "${arr[$c]}"

If it still gives any error, once add set -xv just below script interpreter to debug the script, as:-

Code:

#!/bin/bash
set -xv
total=...
....
.....

flaskvacuum · 01-07-2013, 01:19 AM

Quote:

Originally Posted by shivaa

Code:

DUMP_DIR=${arr[$c]}
	echo "$DUMP_DIR"

What is need to first saving the array element in DUMP_DIR and then printing DUMP_DIR? Instead, you can directly print array element, as:-

Code:

echo "${arr[$c]}"

If it still gives any error, once add set -xv just below script interpreter to debug the script, as:-

Code:

#!/bin/bash
set -xv
total=...
....
.....

everything looks fine just that it keep giving out:
Syntax error at line 7 : `(' is not expected.

not too sure why.

shivaa · 01-07-2013, 02:17 AM

Quote:

Originally Posted by flaskvacuum

everything looks fine just that it keep giving out:
Syntax error at line 7 : `(' is not expected.

It is just because of your script interpretter i.e. shebang. What's it? Set it to:-

Code:

#!/bin/bash

Also check the while condition, and use $total, not just total:

Code:

while [ $c -le $total ]

grail · 01-07-2013, 07:14 AM

Well I have nothing much to add to the issue, but I do have a question ... Why use a while loop like a for loop and not just use a for loop??

Code:

# currently
total=2
c=0
while [ $c -le total ]
do
    ...
    c=`expr $c + 1`
done

# OR
for (( c = 0; c <= total; c++ ))  # yes it is correct that in (()) you do not need '$' in front of variables

# OR is total never changes
for c in {0..2}

Just a thought