bash function definition gives syntax error

Question

I cannot define a bash function only for specific names and when I use <function name>() syntax and when I try to define it in the current shell (i.e. not in a subshell).

$ cat -n test.sh 
1   function f { true; }
2   
3   f() { true; }
4   
5   function make { true; }
6   
7   make() { true; }

$ function f { true; } && f() { true; } #OK

$ function make { true; } && make() { true; } #NG
bash: syntax error near unexpected token `(`

$ bash test.sh #OK

$ source test.sh #NG
bash: test.sh: line 7: syntax error near unexpected token `(`
bash: test.sh: line 7: `make() { true; }'

What's happening here? Is this an expected behavior? I believe, at least, this is not syntax error near unexpected token `(' as the error message suggests.

Environment

$ bash --version
GNU bash, version 5.0.16(1)-release (x86_64-pc-linux-gnu)
Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

It shouldn't matter. You can overwrite a system name. Your syntax looks fine. I'm still looking at it. I can define function make { echo bar; }; make() { echo foo; }; make --version at the command line and as expected, get "foo" back, so I'm a bit confused as to your error. Same GNU bash, version 5.0.16(1)-release (x86_64-pc-linux-gnu) — David C. Rankin
– David C. Rankin, Commented May 5, 2020 at 1:09
@DavidC.Rankin I have yeas of experience on bash, but haven't encountered this problem until today... — ynn
– ynn, Commented May 5, 2020 at 1:11
@JohnKugelman Couldn't reproduce on GNU bash, version 5.0.3(1)-release (arm-unknown-linux-gnueabihf) on Raspberry Pi 3. So maybe the problem is due to my configuration but is it possible to customize bash not to accept specific names in the first place? I haven't modified the source code of bash. — ynn
– ynn, Commented May 5, 2020 at 1:23
I just went through man bash with source as the search term, I can't find anything there that explains it either. — David C. Rankin
– David C. Rankin, Commented May 5, 2020 at 1:23

John Kugelman · Accepted Answer · 2020-05-05 01:25:54Z

6

You have some sort of make alias that's getting triggered. I can reproduce this if I create an alias with purposeful syntax errors:

$ alias make='@)$*)@'
$ make() { true; }
bash: syntax error near unexpected token `)'

Aliases only execute interactively. They're not active inside scripts, which explains why this only happens when you run the command by hand or with source.

answered May 5, 2020 at 1:25

John Kugelman

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2 Comments

ynn Over a year ago

Yes, I set alias make='make --no-builtin-rules' but didn't know it is expanded even in the context of function definitions. Thank you very much.

John Kugelman Over a year ago

I didn't know it either, and didn't expect it. I would have thought the parentheses would inhibit alias expansion, but nope!

ynn · Accepted Answer · 2020-05-05 02:11:07Z

0

The cause of the problem is described in John's answer. I'm writing this answer to give solutions how to avoid the problem.

Solution 1

First undefine the alias and then define the function. Writing like this every time (for safety) seems troublesome, but this is a POSIX-compliant way.

unalias make
make() { true; }

Solution 2

Or use another form of function definitions. This is simple but not POSIX-compliant.

function make { true; }
#or
function make() { true; }

answered May 5, 2020 at 2:11

ynn

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