for cycle

Shell Programming and Scripting
1

Hello,

I have a question:
is there a way to have a "for" cycle done a certain number of times. For example in c++ I can do this:
for (i=o;i<10;i++)
and the cycle will be repeated 10 times.
in UNIX for example I do this:
for i in `cat /etc/host` do done
and the cycle will be repeated depending the item in the file
can something similar be done on UNIX?

thanks

2

yes. depending on the scripting language you're using....

in ksh:

num=0

while [ $num -lt 10 ]; do

  num=$(( num + 1 ))

  echo doing something...

done

not very elegant...

in csh:

repeat 10 echo something

in perl:


for ( 0 .. 9 ){
  print "doing something\n";
  }

HTH

3 
x=1
while [[ $x -lt 10 ]] 
do
     x=$(( $x + 1 ))
done

The for () construct doesn't exist in POSIX shells, just the (shudder) c shell.

4

are you sure?

cjajohnson corrected my use of the idiom:

(( x = x + 1 ))

... saying it wasn't POSIX compliant -- and offered the x=$$(( x + a ))
instead.

I think I'll just give my answers in ksh unless the poster complains
from now on.

5

Try it - it is correct

output with set -x

 t.sh
+ x=1
+ [[ 1 -lt 10 ]]
+ x=2
+ [[ 2 -lt 10 ]]
+ x=3
+ [[ 3 -lt 10 ]]
+ x=4
+ [[ 4 -lt 10 ]]
+ x=5
+ [[ 5 -lt 10 ]]
+ x=6
+ [[ 6 -lt 10 ]]
+ x=7
+ [[ 7 -lt 10 ]]
+ x=8
+ [[ 8 -lt 10 ]]
+ x=9
+ [[ 9 -lt 10 ]]
+ x=10
+ [[ 10 -lt 10 ]]

#!/bin/ksh

set -x
x=1
while [[ $x -lt 10 ]] 
do
     x=$(( $x + 1 ))
done
6

thank so much guys!!!

7

ksh, bash, zsh all accept:

for ((i=0; i < 10; i++)) 
do 
  echo $i;
done