PHP CLI - comma-separated key/value pairs wrapped in curly braces - what are they?

Question

Running PHP script from cli as:

$ php test.php {a=1,b=2,c=3}

Results in $argv structure as:

[
    0 => test.php
    1 => a=1
    2 => b=2
    3 => c=3
]

Question.

What is the intended meaning of { ... } in that case?
Is it a PHP thing or bash thing?
Is there an online documentation that describes this behaviour? (yes, I've googled already - without success)

Thanks!

Possible duplicate of [Curly braces in string in PHP](https://stackoverflow.com/questions/2596837/curly-braces-in-string-in-php) — Lelio Faieta, Jul 09 '19 at 14:25
It has nothing to do with PHP and everything to do with shell parameter expansion — Sean Bright, Jul 09 '19 at 14:26
@LelioFaieta it is not a dupe. At least not a dupe of the question you linked. — Sean Bright, Jul 09 '19 at 14:27
Or from the horse's mouth: https://www.gnu.org/software/bash/manual/bash.html#Brace-Expansion — Sean Bright, Jul 09 '19 at 14:28
Doesn't appear to be bash though, no "$" before the params. Looks like csh/tcsh. — Kevin_Kinsey, Jul 09 '19 at 14:29

score 1 · Accepted Answer · answered Jul 09 '19 at 14:35

Per section 3.5.1 of the Bash manual:

Brace expansion is a mechanism by which arbitrary strings may be generated. This mechanism is similar to filename expansion, but the filenames generated need not exist. Patterns to be brace expanded take the form of an optional preamble, followed by either a series of comma-separated strings or a sequence expression between a pair of braces, followed by an optional postscript. The preamble is prefixed to each string contained within the braces, and the postscript is then appended to each resulting string, expanding left to right.

In your case, there is no preamble or postscript, so it's just expanding to each of the elements in the list.

You can see the result by using echo:

echo {a=1,b=2,c=3}

Which outputs:

a=1 b=2 c=3

If you were to use a preamble and postscript:

echo before{a=1,b=2,c=3}after

You get:

beforea=1after beforeb=2after beforec=3after

I typically use this when trying to copy or move a file to a backup:

cp somefile.txt{,.bak}

Which expands to:

cp somefile.txt somefile.txt.bak

score -1 · Answer 2 · answered Jul 09 '19 at 14:38

-1

{} is represented as an object in PHP, when var_dump an instance of a class, you will se it's wrapped by {}. There is a documentation i found which describe how to use $argv https://www.php.net/manual/en/reserved.variables.argv.php

answered Jul 09 '19 at 14:38

Lam Nguyen

186
1
8

1

The braces are never making it to PHP – Sean Bright Jul 09 '19 at 14:39
Yes, but `PHP` actually has `object type` representation of `{...}`. So when `var_dump` an object, it generate infomation inside `{..}` – Lam Nguyen Jul 09 '19 at 14:44
OK? I don't see what that has to do with this question though. – Sean Bright Jul 09 '19 at 14:45
It's my assumption on how PHP converts data in `CLI`. Because PHP can `eval` the representation of object which is `{...}` to an actual object by `eval`. Your answer seems fit in this case. – Lam Nguyen Jul 09 '19 at 14:48

PHP CLI - comma-separated key/value pairs wrapped in curly braces - what are they?

2 Answers2