bash shellcheck issue with variables in brace expansion

Question

I'm trying to create an array of file names, based on two variable and using brace expansion, like this:

#!/bin/bash
altdir=/usr
arg=abc
tries=({.,$altdir}/{$arg,$arg/main}.{tex,ltx,drv,dtx})
for i in "${tries[@]}"; do echo $i; done

The last statement list the files I want correctly:

./abc.tex
./abc.ltx
./abc.drv
./abc.dtx
./abc/main.tex
./abc/main.ltx
./abc/main.drv
./abc/main.dtx
/usr/abc.tex
/usr/abc.ltx
/usr/abc.drv
/usr/abc.dtx
/usr/abc/main.tex
/usr/abc/main.ltx
/usr/abc/main.drv
/usr/abc/main.dtx

But shellcheck tells me that the two variables, altdir and arg, appear to be unused:

$ shellcheck testscript

In testscript line 3:
    altdir=/usr
    ^-- SC2034: altdir appears unused. Verify it or export it.

In testscript line 4:
    arg=abc
    ^-- SC2034: arg appears unused. Verify it or export it.

Is there a better way to do this?

It seems as a shellcheck's bug. They seem to fail to recognise a variable usage in brace expansion. — choroba, Sep 16 '15 at 15:08
I think you're fine. An unused variable warning is meant to catch typos; if you know you aren't making a mistake, it's safe to ignore it. — Tom Hunt, Sep 16 '15 at 15:22
@WyboDekker shellcheck's commit history suggests that this was fixed in 0.3.8. Your version 0.3.4 is over a year old. — that other guy, Sep 17 '15 at 18:21

score 5 · Accepted Answer · edited Apr 13 '17 at 12:37

5

A workaround can be:

#!/bin/bash

unset altdir
unset arg

: "${altdir:=/usr}"
: "${arg:=abc}"

tries=({.,"$altdir"}/{"$arg","$arg"/main}.{tex,ltx,drv,dtx})
for i in "${tries[@]}"; do echo "$i"; done

or make shellcheck ignore SC2034 code:

shellcheck -e SC2034 testscript

(And remember to always quote your variables if you don't want list context)

edited Apr 13 '17 at 12:37

Community

1

answered Sep 16 '15 at 15:50

cuonglm

153,898

Thanks! After all I found that the online version of shellcheck behaves differently than my Debian-8.1 version (shellcheck-0.3.4). The online version had no problem with my original script, except for the $i that should be quoted. The Debian shellcheck said about the quoted tries= statement: "Use spaces, not commas, to separate array elements. [SC2054]", which is why I removed the quotes. – Wybo Dekker Sep 17 '15 at 10:50

bash shellcheck issue with variables in brace expansion

1 Answers1