Add the word "prefix" to beginning of line using sed

Shell Programming and Scripting
1

SUSE linux
bash shell

this works

test -d /tmpp && echo "directory exists" || echo "directory doesn't exists"  |sed -e "s/^/prefix /"
   prefix directory doesn't exists

but why doesn't this work?

 test -d /tmp && echo "directory exists" || echo "directory doesn't exists"  |sed -e "s/^/prefix /"
   directory exists
2

most likely because /tmpp != /tmp

3

If you want it to work, both echo statements have to be part of one single process, I chose a subprocess:

( test -d /tmp && echo "directory exists" || echo "directory doesn't exists" ) | sed -e "s/^/prefix /"
 prefix directory exists

Otherwise the part after the || is part of the second compound statement (echo )not the first.

5 Likes
4

I guess even a { code block; } is forced into a subshell because of the pipe.
An if-then-fi is a code block, too. The following is unusual but standard

if test -d /tmp; then
  echo "directory exists"
else
  echo "directory doesn't exist"
fi | sed -e "s/^/prefix /"