There are two ways of reading a file line by line that I want to discuss here:
#!/bin/bash
while read line
do
echo-e "$ line \ n"
done <file.txt
and
#!/bin/bash
exec 3<file.txt
while read line
do
echo-e "$ line \ n"
done
So first version works fine but I don't understand the mechanism of working while loop with the file. But the mechanism of the second version I understand. But here I don't understand why it hangs and does not print anything.
The first loop works because the redirection after the done applies to the whole loop, so the read there is reading from the file, not from the standard input of the script.
The second version hangs because read reads from file descriptor 0, which is standard input, and you've not typed anything there. The exec line redirects file descriptor 3 for reading from the file, but you're not reading from file descriptor 3.
You could rescue the second by using:
exec <file.txt
Now standard input is read from the named file.
This might work for you:
exec 3<file.txt
while read -u3 line
do
echo -e "$line \n"
done
-u3 reads from file descriptor 3
Strange that echo does not have the complement switch like ksh's print command.
There are few mistakes in your scripts.
$ and variable name. (may be bad edit)echo and -e. (may be bad edit)It should be something like this -
#!/bin/bash
exec 3<file.txt
while read line
do
echo -e "$line \n"
done <&3
<&3 on the read line work? It used to be the case, back in the bad old days of the real Bourne shell, that the redirection would be done each time round the loop, so you got funny effects (like the file being closed on each iteration). I can well believe it has been modified since then so that things work a little more sanely. FWIW: when I tried bash on MacOS X, with: while read line < somefile; do echo $line; done, I got the first line of somefile echoed repeatedly...but with the <&3 notation, I did get the successive lines of the file. Be careful!
awk and sed. But will start some books on bash basics. :)<&3 after done statement instead of read statement.
-u3 is great for my purpose (reading only the following line)
#!/bin/bash
logs=(*Logs.txt)
[[ -e "${logs[0]}" ]] || exit 0
exec 3<"${logs[0]}"
while read -u3 line
do
if [[ $(echo "$line"| grep -c SCSI_STATUS_CHECK_CONDITION) -eq 1 ]]; then
read -u3 line
echo "$line"
fi
done
