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Script stops running after assigning empty string for a variable

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# 1  
Old 10-11-2011
Script stops running after assigning empty string for a variable
Hi,

This is the first time I see something like this, and I don't why it happens.
Please give me some help. I am really appreciate it.

Basically I am trying to remove all empty lines of an input..

Code:
#!/bin/bash

set -e
set -x

str1=`echo -e "\nhaha" | grep -v ^$`
#str2=`echo -e "\n" | grep -v ^$`
echo "done"

This works fine for str1 (aka I can see "done" as output)
However, if I use str2, after assigning empty string for str2. The script stops there. And I do not see any output at all.

Thanks a lot in advance.
yoyomano
# 2  
Old 10-11-2011
try to echo the values of str1 and str2.. It works for me ..
Code:
$ cat filename
str1=`echo -e "\nhaha" | grep -v ^$`
echo "STR1: $str1"
str2=`echo -e "\n" | grep -v ^$`
echo "STR2: $str2"
[ "$str2" = "" ] && echo "str2 is NULL" || echo "str2 not NULL"
echo "done"
$
$ bash filename
STR1: haha
STR2:
str2 is NULL
done
$

# 3  
Old 10-11-2011
I have managed to use sed instead of grep.

I just change from
Code:
grep -v ^$

to
Code:
sed '/^$/d'

However, I will be really grateful if someone can explain why grep doesn't work.

Thanks a lot in advance.,
# 4  
Old 10-11-2011
Quote:
Originally Posted by yoyomano
I have managed to use sed instead of grep.
However, I will be really grateful if someone can explain why grep doesn't work.

Thanks a lot in advance.,
grep is actually working..why do you think so?
Code:
echo -e "\n"|grep -v ^$

is equal to
Code:
echo -e "\n"|sed '/^$/d'

both of these give same result so is NULL.
# 5  
Old 10-11-2011
The exit code of the assignment is the exit code of the last command of the pipe line which is grep. Since grep didn't find any matching data, it exited with 1. The shell script exited since you have set -e at the beginning.
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