Passing arrays / lists between bash functions without global variables

Question

I have these two functions in a bash script. I am just trying to pass arguments directly from one function to another without using global vars, but I can't seem to do it.

function suman {

  NODE_EXEC_ARGS= "--inspect"; 
  __handle_global_suman "${NODE_EXEC_ARGS}" "$@"

}


function __handle_global_suman {

  # I want $1 to be node exec args and $2 to be args to node script
  node $1 ${Z}/cli.js $2;

}

the problem I am having: in the __handle_global_suman function, the values for $1 and $2 seem to represent the original arguments passed to the suman function, not the arguments passed to __handle_global_suman! I want to be able to access the arguments pass to the __handle_global_suman function.

One solution is to use global variables like the following (but this is bad programming in general):

NODE_EXEC_ARGS="";  // default
ORIGINAL_ARGS="";  // default

function suman {

  NODE_EXEC_ARGS="--inspect";  
  ORIGINAL_ARGS="$@";  // assume this captures the arguments passed to this function, not the original script...
  __handle_global_suman
}

# ideally there would be a way to make this function truly private
function __handle_global_suman {

  # I want $1 to be node exec args and $2 to be args to node script
  node ${NODE_EXEC_ARGS} ${Z}/cli.js ${ORIGINAL_ARGS};

}

hopefully you see what I am trying to do and can help, thanks

Also, if there is a way to make the __handle_global_suman function truly private, that would be a nicety — Alexander Mills
– Alexander Mills, Commented Nov 25, 2016 at 23:47
You can't assign an array to a string without losing argument-boundary information. ORIGINAL_ARGS="$@" is thus inherently broken -- only an array, not a string, can store that value safely. See shellcheck.net for the more pedestrain quoting errors. — Charles Duffy
– Charles Duffy, Commented Nov 26, 2016 at 0:32
...there's also a bunch of general-purpose bad practice here. The function keyword is needlessly incompatible with baseline POSIX sh shells (unlike most bash extensions, adding no value over the portable form, which is suman() { with no preceding function), and all-uppercase variable names are reserved by POSIX-specified convention for variables with meaning to the operating system or shell. — Charles Duffy
– Charles Duffy, Commented Nov 26, 2016 at 0:35
(rather, POSIX explicitly specifies that environment variables with meaning to tools it specifies are all-caps, and that all lower-case environment variables are reserved for application use -- but since setting a shell variable overwrites any like-named environment variable, the only way to be certain one isn't overwriting an environment variable with meaning to the system is to steer clear of the namespace). — Charles Duffy
– Charles Duffy, Commented Nov 26, 2016 at 0:37

Charles Duffy · Accepted Answer · 2016-11-26 00:50:44Z

2

In the below, we're passing an argument list stored in a local variable by reference:

suman() {
   local -a args=( --inspect --debug-brk )
   __handle_global_suman args "$@"
}

__handle_global_suman() {
   local ref="$1[@]"; shift
   node "${!ref}" "${Z}/cli.js" "$@"
}

Why is this different? Because we could also pass:

local -a args=( --inspect --argument-with-spaces="hello cruel world" )

...and it --argument-with-spaces=... would be passed correctly, as exactly one argument.

answered Nov 26, 2016 at 0:50

Charles Duffy

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16 Comments

Alexander Mills Over a year ago

huh, how does local get passed from suman to __handle_global_suman?

Alexander Mills Over a year ago

it would be neat if that local keyword worked for functions, then we could make a private function ?

Charles Duffy Over a year ago

Right. local is a keyword that makes your variables, well, local -- even if declared inside a function, all shell variables are global unless declare, typeset or local is used in their declaration.

Alexander Mills Over a year ago

it would be neat if that local keyword worked for functions, then we could make a private function ?

Charles Duffy Over a year ago

No, you can't make a private function, but... frankly, I'm not sure I see the point.

|

Jonathan Leffler · Accepted Answer · 2016-11-26 05:38:57Z

1

Your explanation is a little unclear, but I think I get the gist: word splitting isn't working as you expected in Bash.

You need to quote the ${NODE_EXEC_ARGS} parameter to you second function, since in the case that it is whitespace it will be stripped out and wont form a parameter to the called function:

__handle_global_suman "${NODE_EXEC_ARGS}" ${ORIGINAL_ARGS}

Also the ${ORIGINAL_ARGS} var is redundant in your example. You should just pass "$@" directly:

__handle_global_suman "${NODE_EXEC_ARGS}" "$@"

The second proposed alternative solution definitely isn't necessary, definitely is bad practice and you can definitely achieve what you want with Bash function parameter passing.

edited Nov 26, 2016 at 5:38

Jonathan Leffler

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answered Nov 26, 2016 at 0:05

spinkus

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11 Comments

Alexander Mills Over a year ago

so if I quote the arguments, then they will get passed properly to the __handle_global_suman function?

Alexander Mills Over a year ago

this is not really working for me, can you let me know what isn't clear in the original question? I am just trying to pass arguments directly from one function to another without using global vars

spinkus Over a year ago

Well, I meant you could have stripped it back to isolate exactly the problem you having. Like what's a "suman" etc. But I get the general jist, your bumping up against a word splitting issue.

Alexander Mills Over a year ago

re: "You also want to probably not quote the $1 when you pass it to node since it multiple args:" Yes, I agree, I will edit the original question to fix that so it's not a distraction.

Charles Duffy Over a year ago

$ORIGINAL_ARGS is not just redundant, it's broken. "foo bar" "baz qux" won't be kept as two words when passed that way, nor will "*.txt" retain its quoting.

|

Alexander Mills · Accepted Answer · 2016-11-26 01:10:13Z

0

Here is what works for me, thanks to the help @S.Pinkus whose answer I upvoted since the information contained in the answer was all I needed to fix the problem. Note the below works, but that @CDhuffy's answer is in theory more generic and therefore better.

function suman {

   __handle_global_suman "--inspect --debug-brk" "$@"

}

function __handle_global_suman {

   # ${1} is "--inspect --debug-brk"
   # ${2} is whatever I passed to the suman function
   node ${1}  ${Z}/cli.js ${2};

}

bash is awesome ;) ...not

edited Nov 26, 2016 at 1:10

answered Nov 26, 2016 at 0:40

Alexander Mills

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7 Comments

Charles Duffy Over a year ago

This code is buggy. If instead of --inspect --debug-brk you wanted to pass --foo="bar baz", it wouldn't work for the reasons described in BashFAQ #50.

Alexander Mills Over a year ago

I see, can you mention a fix?

Charles Duffy Over a year ago

Which specific version of bash? I'd be tempted to use namevars if you're targeting 4.4 or newer.

Alexander Mills Over a year ago

let me check, it says "sh-3.2$"

Alexander Mills Over a year ago

btw it definitely does not work if I just use quotes like so: node "${1}" ${X}/cli.js "${2}";

|

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