Output Redirection in linux to a file by a variable

Question

I have a file pointed to by a user defined environmental variable $file defined as:

file='filename.groovy'

When I do:

echo $file

It prints correctly without any problem as:

filename.groovy

and when I do:

cat $file

Its successfully printing the content of the file 'filename.groovy'

Everything is perfect till here

But, the problem is :

When I'm trying to redirect the output of sed command as:

sed 's/def version = ".*"/def version = "'$version'"/' $file > $file

and then

cat $file

Its printing nothing i.e., my original file got truncated.

Why is it so ?

Please suggest the reason and solution to redirect the output of sed command to the file 'filename.groovy' by using the variable $file

Thanx in advance . . .

Actually I hit `Tab` and `Enter` accidentally, so my question got submitted before I complete and then I got disconnected. Sorry for that... — sivareddy963, Jun 04 '13 at 11:48
How if we want to redirect that output to a different file pointed to by $file2 ? — sivareddy963, Jun 04 '13 at 11:57

score 1 · Accepted Answer · edited May 23 '17 at 12:11

1

You cannot read a file and in the meanwhile redirect your output to it.

What you can do is to use -i parameter in sed, that updates the file:

sed -i 's/def version = ".*"/def version = "'$version'"/' $file

You can see an example in https://stackoverflow.com/a/16901328/1983854 I posted yesterday.

edited May 23 '17 at 12:11

Community

answered Jun 04 '13 at 11:48

fedorqui

How if we want to redirect that output to a different file pointed to by $file2 ? – sivareddy963 Jun 04 '13 at 11:58
1

In that case, `sed 's...' $file1 > $file2` should make the trick. – fedorqui Jun 04 '13 at 11:59
Okey.. Thank you. I got it. So, that means the problem arises only if the redirection is meant to the same file. Am I right? – sivareddy963 Jun 04 '13 at 12:04
Exactly. Like what I get here: `$ cat a > a cat: a: input file is output file`. – fedorqui Jun 04 '13 at 12:05

score 1 · Answer 2 · answered Jun 04 '13 at 11:49

1

> truncates the file before the command is run, but you can use sed -i to replace in a file in-place.

answered Jun 04 '13 at 11:49

l0b0

2 Answers2