for loop using {1..$t}


 
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# 1  
Old 10-14-2012
for loop using {1..$t}

I read here: Bash For Loop Examples
that I should not use seq, instead use {1..10}

I am not getting this to work

old code
Code:
#!/bin/bash
t=$(cat /var/bin/servers | wc -l)
for c in $(seq 1 $t)
        do
                SERVER[$c]=$(awk 'NR==C { print $2 }' C="$c" /var/bin/servers)
        done

new code not working
Code:
#!/bin/bash
t=$(cat /var/bin/servers | wc -l)
for c in {1..$t}
        do
                SERVER[$c]=$(awk 'NR==C { print $2 }' C="$c" /var/bin/servers)
        done

This give error like this error token is "{1..8}"
{1..8} seems to be the correct replacement for $t

also tested this for c in {1..${t}}, not working

This works fine for c in {1..8}, but I need the variable option.
# 2  
Old 10-14-2012
That's useless use of cat , for and wc -l.

You can directly do like this..Smilie

Code:
while read line
do
let ++count
SERVER[$count]=$(echo "$line" | awk '{ print $2 }')
done<file

Hope this helpsSmilie

Last edited by pamu; 10-14-2012 at 06:17 AM..
This User Gave Thanks to pamu For This Post:
# 3  
Old 10-14-2012
Check your bash version..it should be > version 3.0+
# 4  
Old 10-14-2012
Try:
Code:
#!/bin/bash
i=0
while read x srv x
do
  SERVER[i++]=srv
done < file

--
You cannot use a variable inside a { list }
# 5  
Old 10-14-2012
while read does work fine. Smilie

GNU bash, version 4.2.8(1)-release (i686-pc-linux-gnu)
As I told in my first post for i in {1..10} works.

It should be possible to use variable in for loops too.
# 6  
Old 10-14-2012
You can use variables in a for loop like this:
Code:
for (( c=1; c<=t; c++ )); do

This User Gave Thanks to Scrutinizer For This Post:
# 7  
Old 10-14-2012
Quote:
Originally Posted by Jotne
while read does work fine. Smilie

GNU bash, version 4.2.8(1)-release (i686-pc-linux-gnu)
As I told in my first post for i in {1..10} works.

It should be possible to use variable in for loops too.
You can use variables in for loops, but not inside of a {}. Someone else can probably do a better job of explaining this, but the bottom line is it has to do with the order in which the shell interprets what you're putting into it. As I recall (and to be honest, I usually just learn how things work, not why, so you should probably look this up...) the reason is that expanding the {} is the very first thing the shell does, BEFORE it translates the variable into it's value. So, if you're trying to do:

(
Code:
15:45:24\[root@DeCoBoxOmega)
[~]$ x=5

(15:47:46\[root@DeCoBoxOmega)
[~]$ for i in {1..$x};do echo $i;done


What the shell is actually doing is for i in the literal expression {1..$x} because $x doesn't mean anything yet.
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