[arch-projects] [dbscripts] [PATCH 4/8] Use `grep &>/dev/null` instead of `grep -q` when operating on piped stdin.

[Luke Shumaker]

On Wed, 14 Mar 2018 00:11:12 -0400,
Eli Schwartz wrote:
> 
> On 03/13/2018 09:52 PM, Luke Shumaker wrote:
> > From: Luke Shumaker <lukeshu at parabola.nu>
> > 
> > `grep -q` may exit as soon as it finds a match; this is a good optimization
> > for when the input is a file.  However, if the input is the output of
> > another program, then that other program will receive SIGPIPE, and further
> > writes will fail.  When this happens, it might (bsdtar does) print a
> > message about a "write error" to stderr.  Which is going to confuse and
> > alarm the user.
> > 
> > In one of the cases, this had already been mitigated by wrapping
> > bsdtar in "echo "$(bsdtar ...)", as Bash builtin echo doesn't complain
> > if it gets SIGPIPE.  However, that means we're storing the entire
> > output of bsdtar in memory, which is silly.
> > ---
> >  db-functions         | 2 +-
> >  test/lib/common.bash | 4 ++--
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/db-functions b/db-functions
> > index 58b753a..ee390ff 100644
> > --- a/db-functions
> > +++ b/db-functions
> > @@ -303,7 +303,7 @@ check_pkgfile() {
> >  
> >  	in_array "${pkgarch}" "${ARCHES[@]}" 'any' || return 1
> >  
> > -	if echo "${pkgfile##*/}" | grep -q "^${pkgname}-${pkgver}-${pkgarch}"; then
> > +	if echo "${pkgfile##*/}" | grep "^${pkgname}-${pkgver}-${pkgarch}" &>/dev/null; then
> 
> But echo should be fine anyway?

Yeah, in this case it's for consistency with the others.  It's easier
to remember "don't use `grep -q` on other commands' stdout" that it is
to work out when it's ok and when it isn't.

> Regardless this could be so much more elegant.
> 
> if [[ $pkgfile = $pkgname-$pkgver-$pkgrel-$arch* ]]; then

You're right, that is better.

-- 
Happy hacking,
~ Luke Shumaker