rens wrote:
this script:
_______________________
export cval=0
echo entering while
# listing ten files, to generate some output to count.
ls -1 /usr/bin|head -10 |while read fname
do
cval=$(( cval +1 ))
echo cval = $cval file = $fname
done
# one would think cval is now 10. but it is not, contrary to any other
programming language........
echo " after while: cval = $cval"
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does not set the value of cval after exiting the while loop.
that makes no sense.
Bash should not work that way. no programming language handles logic
this way. Not pascal, korn shell, c shell, cobol, c, c++, lua , fortran
or any other language i ever used.
----
Bash is a command-line interpreter. It is not a language;
It accepts commands and has ways of sequencing commands and funneling
output from one command to the next.
Korn shell works the same way. csh has no read builtin that I can
find, so you can't write the program the same way.
Every time you use "|", you are ending the previous program and piping results
to another program.
The above is equal to the *first* 'while' output in the program below:
If you want your progam to work right, you need to have the count be in your
shell, and NOT have any "|" in the invocation line (i used < <(...))
The below produces the wrong output first (cval=0) and then runs it again with
the commands re-arranged to not use '|' -- which produces the right value.
Does this help you understand what's going on?
-------------------------------------------------
#!/bin/bash
shopt -s expand_aliases
alias program=function
alias int=declare\ -i
alias my=declare
program myhead {
my inp=${1:-10}
if [[ ${inp:0:1} == - ]]; then inp="${inp:1}"; fi
int lines=$inp
while ((lines-- > 0)); do
my line
read line
echo "$line"
done
}
declare -xi cval=0
echo entering while
program print_exported_cval {
while [[ ! $(typeset -p cval |sed -r 's/ +/\t/g'|cut -f2) =~ x ]];do
unset cval
done
echo -n "exported_cval=$cval, "
}
program number {
#int cval=$cval
while read fname; do
cval=$cval+1
echo -n "local_cval=$cval, "
(print_exported_cval)
echo "file = $fname"
done
}
#number< <(ls -1 | myhead -10 )
ls -1 | myhead -10 |number
echo " after 1st while: cval = $cval"
number< <(ls -1 | myhead -10 )
echo " after 1st while: cval = $cval"
#end script -----------------------------------------
