Subject: AND list "command1 && command2" doesn't work as expected - msg#00169

From: yafrank@xxxxxxx
To: bug-bash@xxxxxxx
Subject: AND list "command1 && command2" doesn't work
as expected

Configuration Information [Automatically generated, do
not change]:
Machine: i386
OS: linux-gnu
Compiler: i386-redhat-linux-gcc
Compilation CFLAGS: -DPROGRAM='bash'
-DCONF_HOSTTYPE='i386'
-DCONF_OSTYPE='linux-gnu'
-DCONF_MACHTYPE='i386-redhat-linux-gnu'
-DCONF_VENDOR='redhat' -DSHELL -DHAVE_CONFIG_H -I.
-I. -I./include
-I./lib -D_FILE_OFFSET_BITS=64 -O2 -g -pipe
-march=i386 -mcpu=i686
uname output: Linux twinhead 2.4.27-lck1-bsdc #1
日 10月 3 16:05:43 CST
2004 i686 i686 i386 GNU/Linux
Machine Type: i386-redhat-linux-gnu

Bash Version: 2.05b
Patch Level: 0
Release Status: release

Description:
The bash script "Example 26-14. Emulating a push-down
stack" from
"http://www.tldp.org/LDP/abs/html/arrays.html"; works
fine and there is
an excercise to modify the code to support multiple
element push and
pop. The homework I did works fine until I took for
granted the logical
equivalence AND list should give the same result.
Detail follows:
*********************************************************
#!/bin/bash

BP=100
SP=$BP
LOW_LIMIT=0

DATA=

declare -a stack

push () {
for (( i=1; i<=$#; i++)); do
if [ "$SP" -gt "$LOW_LIMIT" ]; then
stack[SP--]="${!i}"
else
echo "Stack full"
break
fi
done
}

pop () {
count=${1:-1}
DATA=""

for ((i=0; i<count; i++)); do

if [ "$SP" -lt "$BP" ]; then
DATA="$DATA ${stack[++SP]}"
else
echo "Stack empty"
break
fi

# Alter the above "if...else...fi" clause using its
logical equivalent
#+ [ "$SP" -lt "$BP" ] && DATA="$DATA
${stack[++SP]}" || \
#+ { echo "Stack empty"; break; }
#+ won't give the same result. This is not expected.

done
}

status () {
echo "-------------------------------------"
echo "REPORT"
echo "Stack Pointer = $SP"
echo "Just popped \""${DATA# }"\" off the stack."
echo "-------------------------------------"
}

pop # empty stack popup
status # If AND list used in pop(), reports
"SP=101" here

echo
push garbage
pop
status

v1=23; v2=skiddo; v3=final

echo
push $v1 $v2 $v3
status
pop
status
pop 2
status

exit 0
*********************************************************
The bash manual says that for "command1 && command2",
"command2 is executed if, and only if, command1
returns an
exit status of zero." It seems conflict here to the
first
status report "SP=101", which means SP increased by
one even
if "[ "$SP" -lt "$BP" ]" returns non zero when pop an
empty
stack. Is there anything wrong here?

Repeat-By:
Everytime the "if...else...fi" in pop() replaced by
logical equivalence AND/OR list as in the comment.



Regards

---Frank Wang


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