Shell script “for” loop syntax

Question

I have gotten the following to work:

for i in {2..10}
do
    echo \"output: $i\"
done

It produces a bunch of lines of output: 2

Answer 1

This is a way:
Bash:

max=10
for i in $(bash -c "echo {2..${max}}"); do echo $i; done

The above Bash way will work for ksh and zsh too, when bash -c is replaced with ksh -c or zsh -c respectively.

Note: for i in {2..${max}}; do echo $i; done works in zsh and ksh.

Answer 2

We can iterate loop like as C programming.

#!/bin/bash
for ((i=1; i<=20; i=i+1))
do 
      echo $i
done

Answer 3

Well, as I didn't have the seq command installed on my system (Mac OS X v10.6.1 (Snow Leopard)), I ended up using a while loop instead:

max=5
i=1

while [ $max -gt $i ]
do
    (stuff)
done

*Shrugs* Whatever works.

Answer 4

Brace expansion, {x..y} is performed before other expansions, so you cannot use that for variable length sequences.

Instead, use the seq 2 $max method as user mob stated.

So, for your example it would be:

max=10
for i in `seq 2 $max`
do
    echo "$i"
done

Answer 5

Try the arithmetic-expression version of for:

max=10
for (( i=2; i <= $max; ++i ))
do
    echo "$i"
done

This is available in most versions of bash, and should be Bourne shell (sh) compatible also.