I am having a bash script which is something like following,
cat filename | while read line
do
read input;
echo $input;
done
but this is clearly not giving me the right output as when I do read in the while loop it tries to read from the file filename because of the possible I/O redirection.
Any other way of doing the same?
Read from the controlling terminal device:
read input </dev/tty
more info: http://compgroups.net/comp.unix.shell/Fixing-stdin-inside-a-redirected-loop
bash yourscript < /foo/bar will wait for user input, this is acceptable only when reading passwords. The answer by @GordonDavisson is preferable for all other uses.
You can redirect the regular stdin through unit 3 to keep the get it inside the pipeline:
{ cat notify-finished | while read line; do
read -u 3 input
echo "$input"
done; } 3<&0
BTW, if you really are using cat this way, replace it with a redirect and things become even easier:
while read line; do
read -u 3 input
echo "$input"
done 3<&0 <notify-finished
Or, you can swap stdin and unit 3 in that version -- read the file with unit 3, and just leave stdin alone:
while read line <&3; do
# read & use stdin normally inside the loop
read input
echo "$input"
done 3<notify-finished
read line is reading from notify-finished, but if you just run it as written read -u 3 input is reading from the console)?
read: 3: invalid file descriptor: Bad file descriptor when tryiing to do read -u 33<&0 part in the redirect after done (but before the redirect from the input file)? That's what sets up file descriptor 3.
cat input_file | while also has the benefit, that inside the while loop, you can modify variables of the parent scope. see also A variable modified inside a while loop is not remembered. the cat input_file could be moved to a process substitution like done 3< <(cat input_file)Try to change the loop like this:
for line in $(cat filename); do
read input
echo $input;
done
Unit test:
for line in $(cat /etc/passwd); do
read input
echo $input;
echo "[$line]"
done
I have found this parameter -u with read.
"-u 1" means "read from stdout"
while read -r newline; do
((i++))
read -u 1 -p "Doing $i""th file, called $newline. Write your answer and press Enter!"
echo "Processing $newline with $REPLY" # united input from two different read commands.
done <<< $(ls)
read -u 2.
read -u 2echo "Enter the Programs you want to run:"
> ${PROGRAM_LIST}
while read PROGRAM_ENTRY
do
if [ ! -s ${PROGRAM_ENTRY} ]
then
echo ${PROGRAM_ENTRY} >> ${PROGRAM_LIST}
else
break
fi
done
