Parsing nested arguments

Question

I am not able to parse the arguments of a script properly. The scenario is explained below.

First script (test2.sh):

#! /bin/sh
arg_part1="./test1.sh '123 789'"
arg_part2=456

#Option 1
${arg_part1} ${arg_part2} 

#Option 2
$("$arg_part1" arg_part2)

Second script (test1.sh):

#! /bin/sh
echo "Hello World $1 $2"

Output:

Hello World '123 789'
./test1.sh '123 789': No such file or directory

Desired output:

Hello World 123 789 456

The '123 789' should be processed as first argument and 456 should be my second argument. Note: I do not have the option of breaking up arg_part1 in two different variables.

Stéphane Chazelas · Accepted Answer · 2022-09-07 15:07:23Z

You could keep using the split+glob operator (those unquoted ${arg_part1} and ${arg_part2}), but use a different separator for the split part (as some of the elements contain one of the default separators (space)). You'd also want to disable the glob part.

#! /bin/sh -
arg_part1='./test1.sh|123 789'
arg_part2=456

IFS='|'  # split unquoted expansions on | instead of default SPC+TAB+NL
set -o noglob # disable the glob part (not that it would have any effect
              # in this particular case).

$arg_part1 $arg_part2 # invoke split+glob

# or since you're not intending to split $arg_part2
$arg_part1 "$arg_part2"

To store code, functions are often more appropriate than variables:

arg_part1() { ./test1.sh '123 789' "$@"; }
arg_part2=456

arg_part1 "$arg_part2"

and you don't have to mess-up with the split+glob operator, or use the dangerous eval.

Jeff Schaller · Accepted Answer · 2017-11-16 16:46:46Z

2

I think you're "stuck" needing to use eval here, so that arg_part1 is reinterpreted as a command string, which is then parsed into a command and arguments:

#! /bin/sh
arg_part1="./test1.sh '123 789'"
arg_part2=456
eval "${arg_part1}" "${arg_part2}"

Output:

Hello World 123 789 456

Debug output:

$ sh -x test2.sh
+ arg_part1='./test1.sh '\''123 789'\'''
+ arg_part2=456
+ eval './test1.sh '\''123 789'\''' 456
++ ./test1.sh '123 789' 456
Hello World 123 789 456

Note that since you've inner-quoted '123 789', they appear as a single $1 argument to test1.sh.

edited Nov 16, 2017 at 16:46

answered Nov 16, 2017 at 16:16

Jeff Schaller♦

68.8k35 gold badges122 silver badges267 bronze badges

Even though you're using eval, the variables should still be quoted to prevent filename expansion: eval "$arg_part1 $arg_part2"

glenn jackman
– glenn jackman

2017-11-16 16:42:22 +00:00
Commented Nov 16, 2017 at 16:42

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