Advanced Bash−Scripting Guide

exit 0

There is an alternative, and perhaps less confusing method of redirecting a function's stdin. This involves redirecting the stdin to an embedded bracketed code block within the function.

#Instead of: Function ()

{

...

}< file

#Try this: Function ()

{

{

...

}< file

}

#Similarly,

#Thanks, S.C.

23.2.Local Variables

What makes a variable "local"?

local variables

A variable declared as local is one that is visible only within the block of code in which it appears. It has local "scope". In a function, a local variable has meaning only within that function block.

Example 23−8. Local variable visibility

Advanced Bash−Scripting Guide

echo "\"global_var\" in function = $global_var"

}

func

# Now, see if local 'a' exists outside function.

echo

echo "\"loc_var\" outside function = $loc_var"

# "loc_var" outside function =

# Nope, $loc_var not visible globally. echo "\"global_var\" outside function = $global_var"

# "global_var" outside function = 999

# $global_var is visible globally.

echo

exit 0

Before a function is called, all variables declared within the function are invisible outside the body of the function, not just those explicitly declared as local.

echo "global_var = $global_var" # global_var =

# Function "func" has not yet been called, #+ so $global_var is not visible here.

func

echo "global_var = $global_var" # global_var = 37

#Has been set by function call.

23.2.1.Local variables make recursion possible.

Local variables permit recursion, [52] but this practice generally involves much computational overhead and

is definitely not recommended in a shell script. [53]

Example 23−9. Recursion, using a local variable

#Does bash permit recursion?

#Well, yes, but...

#You gotta have rocks in your head to try it.

Advanced Bash−Scripting Guide

MAX_ARG=5

E_WRONG_ARGS=65

E_RANGE_ERR=66

if [ −z "$1" ] then

echo "Usage: `basename $0` number" exit $E_WRONG_ARGS

fi

if [ "$1" −gt $MAX_ARG ] then

echo "Out of range (5 is maximum)."

#Let's get real now.

#If you want greater range than this,

#rewrite it in a real programming language. exit $E_RANGE_ERR

fi

fact ()

{

local number=$1

#Variable "number" must be declared as local,

#otherwise this doesn't work.

if [ "$number" −eq 0 ] then

See also Example A−11 for an example of recursion in a script. Be aware that recursion is resource−intensive and executes slowly, and is therefore generally not appropriate to use in a script.