Question

I am new to bash, but this should be a very common scenario. I have the following bash “pseudoscript”

VAR1=oldValue
VAR2=var2

COMMAND="-option1 "$VAR1" -option2 "$VAR2

run $COMMAND $OTHERSTUFF

VAR1=newValue

run $COMMAND $OTHERSTUFF
#$COMMAND is stil using oldValue

Should I use eval to generate a new value for the COMMAND variable?

Answer 1

Use an array

options=( -option1 x -option2 y )

options[1]=oldValue
options[3]=var2
run "${options[@]}" "$OTHERSTUFF"

options[1]=newValue
run "${options[@]}" "$OTHERSTUFF"

If you don’t want to assign directly to the array, use functions to encapsulate the gory details:

initialize_options() { options=( -option1 x -option2 y ); }

set_first()  { set_value 1 "$1"; }
set_second() { set_value 3 "$1"; }
set_value()  { option[$1]="$2"; }

initialize_options

set_first oldValue
set_second var2
run "${options[@]}" "$OTHERSTUFF"

set_first newValue
run "${options[@]}" "$OTHERSTUFF"

---

Thought just occurred to me — this might be simpler:

do_run() { run -option1 "$1" -option2 "$2" "$OTHERSTUFF"; }

VAR1=oldValue
VAR2=var2
do_run "$VAR1" "$VAR2"

VAR1=newValue
do_run "$VAR1" "$VAR2"