fix consistency in binary execution and existance checking

 - prefer using `which` over hard coded paths
 - it is redundant to check that the bin pointed to the return of
   `which` exists and is executable, `which` already gives us
   assurance of that if it returns true!
 - the redirection of output (`2>/dev/null`) seems to be
   unnecessary from my testing.

the instances relatnig to fdisk and losetup in functions/defaults.sh have
been left as they are since they get executed by `lb config` which can run
without sudo elevation unlike `lb build` and in that case `which` would
fail to find these binaries resulting in error.

this also fixes a bug showing an error for missing debootstrap - this tool
requires sudo privileges to run and thus is not found via a none elevated
which search.

Gbp-Dch: Short
Closes: #952927

2 files changed, 3 insertions, 3 deletions

diff --git a/frontend/lb b/frontend/lb
index 0e826d989..f2015b033 100755
--- a/frontend/lb
+++ b/frontend/lb
@@ -20,7 +20,7 @@ USAGE="lb {clean|config|build}"
 
 case "${1}" in
 	-h|--help)
-		if [ -x "$(which man 2>/dev/null)" ]
+		if [ $(which man) ]
 		then
 			man lb
 			exit 0
@@ -75,7 +75,7 @@ case "${1}" in
 		then
 			# User has live-build installed in the system
 			SCRIPT=/usr/lib/live/build/"${COMMAND}"
-		elif [ -x "$(which ${COMMAND} 2>/dev/null)" ]
+		elif [ $(which "${COMMAND}") ]
 		then
 			# User has live-build commands in path
 			SCRIPT="${COMMAND}"
diff --git a/frontend/live-build b/frontend/live-build
index 52b843730..dfd1e4667 100755
--- a/frontend/live-build
+++ b/frontend/live-build
@@ -22,7 +22,7 @@
 
 set -e
 
-if [ -x "$(which man 2>/dev/null)" ]
+if [ $(which man) ]
 then
 	man live-build
 else