[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

bash dislikes empty functions or flow control bodies

From: l . bashbug
Subject: bash dislikes empty functions or flow control bodies
Date: Tue, 18 Jan 2022 12:44:46 +0100

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -g -O2 -fstack-protector-strong -Wformat 
-Werror=format-security -Wall 
uname output: Linux latitude 5.15.0-2-amd64 #1 SMP Debian 5.15.5-2 (2021-12-18) 
x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.1
Patch Level: 16
Release Status: release

Even if descriptions of situations where this problem occurs may sound
contrived, those situation exist and require me to catch this problem
with additional code:
   a: defining an empty function will throw a syntax error
   b: defining an empty bodies flow control construct will thow a syntax error

While it may be debatable whether such construct could serve any purpose
(they actually can), perceived lack of purpose doesn't qualify them as
syntactically wrong. They aren't. Would they be syntactically wrong,
the syntax error would continue to exist after adding a harmless
"no operation" equivalent.

You may justifiable ask "so why not simply use the workaround by adding
a no operation equivalent" - answer is that it may not be me in person
creating a function or a flow control construct - the script may do too,
in accordance with input it received (this is the mentioned part where the
description may sound contrived, but isn't). Therefore I must protect the
script at this point from generating empty functions or flow control

You may have guessed here that this is going towards some sort of meta
programming, and a fuller view of the reason for reporting the bug can be
obtained at https://github.com/Bushmills/yoda, specifically 
at https://github.com/Bushmills/yoda/issues/7
Measures to circumvent the problem can be found in file
https://github.com/Bushmills/yoda/blob/main/yoda at around line 1900 
(at this time) on those lines with text "empty function" in the description

        bar() { ; }
        foo() { if true; then ; fi; }
        foo() { while :; do ; done; }

In cases where this problem arises, I tend to synthesise the closest
approximation of a "no operation" I know about, which is ":":
        bar() { :; }
        foo() { if true; then :; fi; }
        foo() { while :; do :; done; }

reply via email to

[Prev in Thread] Current Thread [Next in Thread]