When i am using the below syntax to iterate why two brackets are needed ?
for (( expr1; expr2; expr3 ))
do
command1
command2
..
done
and the below code doesn't work ? and throws error "syntax error near unexpected token `('"
for ( expr1; expr2; expr3 )
do
command1
command2
..
done
The reason for this is ( has a different meaning. From the bash manpage:
(list) list is executed in a subshell environment
(see COMMAND EXECUTION ENVIRONMENT below). Variable
assignments and builtin commands that affect the shell's
environment do not remain in effect after the command
completes. The return status is the exit status of list.
((expression))
The expression is evaluated according to the rules
described below under ARITHMETIC EVALUATION. If
the value of the expression is non-zero, the return
status is 0; otherwise the return status is 1. This is
exactly equivalent to let "expression".
