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Wednesday, April 22, 2009

sed and Nix Quotation Confusion

I wanted to use "sed" inside a script to make changes to a text file. The file looked like this:

** Project "OrderCache.7.7.29"
** Hint: deleting everything below the "cause" field will set
** the defaults appropriately for the cause you have chosen.
brief_description = "none";
description = "none";
cause = internal_bug;
test_exempt = true;
test_baseline_exempt = true;
regression_test_exempt = true;
architecture =

I wanted to replace the "brief_description" with a value given by the user. So:

set DESC = "$<"

But when I tried to use sed with $DESC:

sed -i 's%brief_description\ \=\ \"none\"\;%brief_description\ \=\ \"$DESC\"\;%g' temp_next.txt

the command would only change "brief_description" as follows:

brief_description = "$DESC";

The reason for this is that the variable has to be inside double quotes in order to get it dereferenced back to the actual value. So the solution is:

sed -i 's%brief_description\ \=\ \"none\"\;%brief_description\ \=\ \"'"$DESC"'\"\;%g' temp_next.txt

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