Looping on variable having new line \n fails


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# 1  
Looping on variable having new line \n fails

I have a for loop that constructs a variable "filelistonly" having entries separated by "\n" new line.

The second, third & fourth while loops are my attempt to iterate the variable "filelistonly" upon new line "\n", however non of them work.

Below is my script:

Code:
//First Loop
for i in $(echo $1 | tr ',' '\n')
do
    fileresult=`find $i -name hello.db -type f`
    filelistonly=$filelistonly`echo ${fileresult%:*}`"\n"
done

//Second Loop
while read -r line; do
echo "*** $line ***"
done <<< "$filelistonly"

//Third Loop
while read line; do
echo line="$line";
done < <(echo "$filelistonly" | tr ',' '\n')

//Fourth Loop
while read -r line; do
    if [ $line != "\n" ]; then
           echo "We are Good. $line File Found."
    else
        echo "New Line Found.... Ignoring"
    fi
done <<< "$filelistonly"

Below is the debug Output:

Quote:
# bash -x ./test.sh /root,/tmp
++ echo /root,/tmp
++ tr , '\n'
+ for i in '$(echo $1 | tr '\'','\'' '\''\n'\'')'
++ find /root -name hello.db -type f
+ fileresult=/root/Music/hello.db
++ echo /root/Music/hello.db
+ filelistonly='/root/Music/hello.db\n'
+ for i in '$(echo $1 | tr '\'','\'' '\''\n'\'')'
++ find /tmp -name hello.db -type f
+ fileresult=/tmp/hello.db
++ echo /tmp/hello.db
+ filelistonly='/root/Music/hello.db\n/tmp/hello.db\n'
+ read -r line
+ echo '*** /root/Music/hello.db\n/tmp/hello.db\n ***'
+ read -r line
+ read line
++ echo '/root/Music/hello.db\n/tmp/hello.db\n'
++ tr , '\n'
+ echo line=/root/Music/hello.dbn/tmp/hello.dbn
line=/root/Music/hello.dbn/tmp/hello.dbn
+ read line
+ read -r line
+ '[' '/root/Music/hello.db\n/tmp/hello.db\n' '!=' '\n' ']'
+ echo 'We are Good. /root/Music/hello.db\n/tmp/hello.db\n File Found.'
We are Good. /root/Music/hello.db\n/tmp/hello.db\n File Found.
+ read -r line
The below code works and resolves the new line problem reported above however the if condition fails which is shown in debug below.
Code:
    filelistonly=$filelistonly`echo ${fileresult%:*}`$'\n'

Output showing if condition failing.....
Quote:
+ '[' /tmp/hello.db '!=' '\n' ']'
+ echo 'We are Good. /tmp/hello.db File Found.'
We are Good. /tmp/hello.db File Found.
+ read -r line
+ '[' '!=' '\n' ']'
./test.sh: line 22: [: !=: unary operator expected
+ echo 'New Line Found.... Ignoring'
New Line Found.... Ignoring
I guess the issue could be in the first loop where I'm constructing the variable "filelistonly", however I'm not sure of a solution yet.

Last edited by mohtashims; 2 Weeks Ago at 02:06 PM..
# 2  
try: if [ "$line" != "\n" ] in case $line is an empty string.
This User Gave Thanks to rdrtx1 For This Post:
# 3  
You can simplify your loops by controlling the special IFS variable. The shell itself can be told to split on newlines and only newlines, or on commas, or quotes, or whatever.

Code:
OLDIFS="$IFS"
# Yes, looks funny, but its a single newline in double-quotes
IFS="
"
STR="string
containing lots of
newlines and
stuff"

for X in $STR
do
        echo "X is $X"
done

# Restore normal splitting behavior
IFS="$OLDIFS"

Also, some of those echoes look redundant.

Code:
filelistonly="${filelistonly}${fileresult%:*}\n"

...and most of those \n's in your code aren't real newlines:

Code:
$ echo "\n"

\n

$

So I suspect a lot of your code isn't doing what you think it is.

Last edited by Corona688; 2 Weeks Ago at 02:49 PM..
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