Variable transformation does not work with arrays

Using "${array[@]@Q}" does not work as expected (I tried some other operators as well and assume this applies to all operators, not just @Q specifically).

$ bash -c 'var="with space"; echo "${var@Q}"'
'with space'
$ : works as expected
$ gosh -c 'var="with space"; echo "${var@Q}"'
'with space'
$ bash -c 'var=("some" "with space"); echo "${var[@]@Q}"'
'some' 'with space'
$ : does not work as expected
$ gosh -c 'var=("some" "with space"); echo "${var[@]@Q}"'
some with space

As you can see, in the last line the result is not quoted.

For the unaware (such as myself): The ${parameter@operator} is not in my local bash man page, I had to go looking for it. It came out in bash 4.4, circa late 2015. See https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html and search for ${parameter@operator}.

The @Q operator:

The expansion is a string that is the value of parameter quoted in a format that can be reused as input.

There are 9 other operators defined in the GNU Bash documentation. This package handles only @Q and @E, everything else panics. See

sh/expand/param.go

Lines 315 to 337 in 793d364

    
           case syntax.OtherParamOps: 
        
           	switch arg { 
        
           	case "Q": 
        
           		str, err = syntax.Quote(str, syntax.LangBash) 
        
           		if err != nil { 
        
           			// Is this even possible? If a user runs into this panic, 
        
           			// it's most likely a bug we need to fix. 
        
           			panic(err) 
        
           		} 
        
           	case "E": 
        
           		tail := str 
        
           		var rns []rune 
        
           		for tail != "" { 
        
           			var rn rune 
        
           			rn, _, tail, _ = strconv.UnquoteChar(tail, 0) 
        
           			rns = append(rns, rn) 
        
           		} 
        
           		str = string(rns) 
        
           	case "P", "A", "a": 
        
           		panic(fmt.Sprintf("unhandled @%s param expansion", arg)) 
        
           	default: 
        
           		panic(fmt.Sprintf("unexpected @%s param expansion", arg)) 
        
           	}

.

Edit: And, obviously, it doesn't work for arrays, regardless.

Ah, it seems you are right about only Q and E being supported. I remember trying @K as well, but it seems it did not error because I tried it for arrays. The following "succeeds" in the sense that it does not error, but the output is still wrong (which makes sense if expansion operators are just ignored for arrays)

$ gosh -c 'var=("some" "with space"); echo "${var[@]@K}"'
some with space

expand: apply per-element operators to quoted array expansions

interp: add test cases for ${var@op} on arrays

expand: implement ${var@op} operators on arrays like Bash

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Variable transformation does not work with arrays #1081

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	case syntax.OtherParamOps:
	switch arg {
	case "Q":
	str, err = syntax.Quote(str, syntax.LangBash)
	if err != nil {
	// Is this even possible? If a user runs into this panic,
	// it's most likely a bug we need to fix.
	panic(err)
	}
	case "E":
	tail := str
	var rns []rune
	for tail != "" {
	var rn rune
	rn, _, tail, _ = strconv.UnquoteChar(tail, 0)
	rns = append(rns, rn)
	}
	str = string(rns)
	case "P", "A", "a":
	panic(fmt.Sprintf("unhandled @%s param expansion", arg))
	default:
	panic(fmt.Sprintf("unexpected @%s param expansion", arg))
	}

Variable transformation does not work with arrays #1081

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theclapp commented on Jul 5, 2024

PigeonF commented on Jul 5, 2024

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