[bash] gawk curiosity: `backticks` work fine , but switching to $(this) doesn't

GrapefruiTgirl · 11-30-2009, 01:53 PM

Code:

root@reactor:/etc/rc.d/lutelwall# service=$(echo $aservice | gawk '{ gsub("\\\(.*\\\)","") ; print }' )
gawk: warning: escape sequence `\(' treated as plain `('
gawk: warning: escape sequence `\)' treated as plain `)'

root@reactor:/etc/rc.d/lutelwall# service=`echo $aservice | gawk '{ gsub("\\\(.*\\\)","") ; print }' `
root@reactor:/etc/rc.d/lutelwall#

So, it isn't a big deal, I'm just curious if anyone has a good idea why the above gawk function gives the warning when $() are around it, but when using backticks, it's fine. In theory, I should be able to use $() right?

This line is from a much larger script, which I went through the other day and replaced literally dozens of gawk+backtick usage with $() to modernize it, and every other instance seems fine; just this single line acts up.

I can leave the backticks, but would like to know what it is about this particular line that's so special..

Sasha

pixellany · 11-30-2009, 01:59 PM

$ needs to be in double-quotes.

Single quotes (AKA "hard quotes") protects everything from being expanded by the shell.

GrapefruiTgirl · 11-30-2009, 02:07 PM

I tried it with double quotes, like:

blah="$( foo foo foo )"

and it still did the same. Is this how you mean?

pixellany · 11-30-2009, 02:15 PM

Sorry---what I was referring to was an expanded variable inside a more complex quoted string.

example:

Code:

[mherring@mystical ~]$ vari="she"
[mherring@mystical ~]$ echo $vari
she
[mherring@mystical ~]$ sed 's/$vari/HERE/' words
this
is
a test
the quick brown fox
she sells seashells
[mherring@mystical ~]$ sed "s/$vari/HERE/" words
this
is
a test
the quick brown fox
HERE sells seashells

catkin · 11-30-2009, 02:42 PM

Quote:

Originally Posted by GrapefruiTgirl

I can leave the backticks, but would like to know what it is about this particular line that's so special..

Puzzling ... it says here that backslashes are handled differently inside backticks but I'm too tired to work out why that results in the symptoms you describe. Goodnight!