Environment variable substitution in sed

linux unix shell sed
RomanM picture RomanM · Feb 25, 2009 · Viewed 264.2k times · Source

If I run these commands from a script:

#my.sh
PWD=bla
sed 's/xxx/'$PWD'/'
...
$ ./my.sh
xxx
bla

it is fine.

But, if I run:

#my.sh
sed 's/xxx/'$PWD'/'
...
$ ./my.sh
$ sed: -e expression #1, char 8: Unknown option to `s'

I read in tutorials that to substitute environment variables from shell you need to stop, and 'out quote' the $varname part so that it is not substituted directly, which is what I did, and which works only if the variable is defined immediately before.

How can I get sed to recognize a $var as an environment variable as it is defined in the shell?

Answer

Norman Ramsey picture Norman Ramsey · Feb 25, 2009

Your two examples look identical, which makes problems hard to diagnose. Potential problems:

  1. You may need double quotes, as in sed 's/xxx/'"$PWD"'/'

  2. $PWD may contain a slash, in which case you need to find a character not contained in $PWD to use as a delimiter.

To nail both issues at once, perhaps

sed 's@xxx@'"$PWD"'@'

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