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fnc() {
local x="this variable is local in scope to this function"
echo $x
}
passf() {
# use local for safety, but will not be avail outside script...
#local user
#local pass
echo -n "username: "
read user
stty -echo
echo -n "password: "
read pass
stty echo
echo -e ""
}
passf_do() {
passf
echo $user
echo $pass
}
#----------------------------------------------------------------------------
demonstrate use of awk method
#returns days in month
monthd() {
local monthd="31 28 31 30 31 30 31 31 30 31 30 31"
echo "$monthd" | awk '{ print $'"${1}"' }'
} ; #monthd $1
# demonstrate use of stdin to function
stdinf() {
while read line; do
echo "$line" | grep $1 | awk -F":" '{ print $5 }' # Have awk use ":" delimiter.
done
} </etc/passwd #$file # redirect into function's stdin.
#pattern=gnats
#stdinf $pattern # $1
#----------------------------------------------------------------------------
dereferencing a parameter passed to a function
dref() {
y=\$"$1" # name of variable
#echo $y # $xvar
x=`eval "expr \"$y\" "`
echo $1=$x
eval "$1=\"new text \"" # assign new value
}
dref_do() {
xvar="just text"
echo $xvar "before" # just text before
dref xvar
echo $xvar "after" # Some Different Text after
}
#----------------------------------------------------------------------------
Indirect References to Variables
Of what practical use is indirect referencing of variables? It gives Bash a
little of the functionality of pointers in C, for instance, in table lookup.
Indirect references also allows building "dynamic" variable names and the
ability to evaluate their contents which can be useful when sourcing
configuration files.
Bash does not support pointer arithmetic, and this severely limits the
usefulness of indirect referencing.
indirect references can be accomplished with two different methods:
2) eval \$$x - bash v1 and up
1) ${!x} - bash v2 and up
passing an indirect reference to a function
echof() {
r=$1
echo "$r"
}
indirect_ref() {
x=y
y=z
echof "$x" #: y
echof "${!x}" #: z
echo "${!x}" #: z
}
dynamic variable name generation using indirect references
dynvar() {
dyn=dynvar_$1 # create dynamic variable handle
eval "$dyn=x" # assign value to dynamic variable
echo $dyn #: dynvar_xyz - direct reference.
echo ${!dyn} #: x - indirect reference.
#alternate method: eval a=\$$a
eval echo \$$dyn #: x - indirect reference.
eval dyn=\$$dyn #: change handle to hold the value.
echo $dyn #: x - indirect reference.
}
dynvar xyz
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