Example:
$ eval echo "{x,y,z}\ --opt\; " x --opt; y --opt; z --opt; Assume that the 2nd list is {1,2,3} and its length is equal to the length of the 1st (initial) list.
Questions:
bash produce:x --opt 1; y --opt 2; z --opt 3; bash produce (i.e. to refer the elements from the {x,y,z} list):x --opt x; y --opt y; z --opt z; One-liners are preferred.
Brace expansion would create all possible pairs, it doesn't walk both the lists in parallel:
$ echo {x,y,z}' --opt; '{1,2,3} x --opt; 1 x --opt; 2 x --opt; 3 y --opt; 1 y --opt; 2 y --opt; 3 z --opt; 1 z --opt; 2 z --opt; 3 To produce the desired output, you need to use something else. For example, loop over the indices of an array:
#! /bin/bash opt1=(x y z) opt2=(1 2 3) for i in "${!opt1[@]}" ; do printf '%s --opt %s; ' "${opt1[i]}" "${opt2[i]}" done echo Or, use associative arrays:
#! /bin/bash declare -A opts=([x]=1 [y]=2 [z]=3) for i in "${!opts[@]}" ; do printf '%s --opt %s; ' "$i" "${opts[$i]}" done echo As choroba pointed out, using {x..z}' --opt '{1..3}';' would generate all possible combinations of strings.
From the list of all possible combinations, 1 through to 9, we want every fourth combination, 1, 5, and 9.
set -- {x..z}' --opt '{1..3}';' eval echo '${'{1..9..4}'}' Or, using arrays, fetching elements 0, 4, and 8.
strings=( {x..z}' --opt '{1..3}';' ) eval echo '${strings['{0..8..4}']}' Note that I would never ever write real code like this and that the code above generates strings that are virtually useless for use as real commands/arguments as they would need to be explicitly split by the shell.
The code is purely presented as an interesting tidbit.
