shell: Using sed in backticks

Question

I want to escape some special chars inside a string automatically. I thought of echoing that string and pipe it through some seds. This doesn't seem to work inside of backticks. So why does

echo "foo[bar]" | sed 's/\[/\\[/g'

return

foo\[bar]

but

FOO=`echo "foo[bar]" | sed 's/\[/\\[/g'` && echo $FOO

just returns

foo[bar]

?

In contrast to sed, tr works perfectly inside of backticks:

FOO=`echo "foo[bar]" | tr '[' '-' ` && echo $FOO

returns

foo-bar]

score 16 · Answer 1 · answered Sep 29 '09 at 13:19

16

How about not using backticks but use $() ?

FOO=$(echo "foo[bar]" | sed 's/\[/\\[/g') && echo $FOO

if you insist on using backticks, I think you need to extra escape all \ into double \

FOO=`echo "foo[bar]" | sed 's/\\[/\\\\[/g'` && echo $FOO

answered Sep 29 '09 at 13:19

fforw

5,391
1
18
17

5

+1 for `$()` Never, ever use backticks. There are so many advantaged to using `$()`. http://mywiki.wooledge.org/BashFAQ/082 – Dennis Williamson Sep 29 '09 at 13:29
3

and +1 for the comment referring to Bash FAQ 82 – nos Sep 29 '09 at 13:33

score 8 · Accepted Answer · answered Sep 29 '09 at 13:23

8

You need to escape the backslashes between the backticks.

FOO=`echo "foo[bar]" | sed 's/\\[/\\\\[/g'` && echo $FOO

Alternatively, use $() (this is actually the recommended method).

FOO=$(echo "foo[bar]" | sed 's/\[/\\[/g') && echo $FOO

answered Sep 29 '09 at 13:23

Alex Barrett

16,175
3
52
51

score 2 · Answer 3 · answered Sep 29 '09 at 13:23

2

Usually, it's a case of underescaping

FOO=`echo "foo[bar]" | sed 's/\[/\\\[/g'` && echo $FOO

answered Sep 29 '09 at 13:23

Michael Krelin - hacker

138,757
24
193
173

shell: Using sed in backticks

3 Answers3

Linked

Related