Xtykutl

I'm using PWD to get the present working directory. Is there a SED or regex that I can use to, say, get the full path two parents up?

Why sed or regex? Why not dirname:

parent=`dirname $PWD`

grandparent=`dirname $parent`

Edit:

@Daentyh points out in the comments that apparently $() is preferred over backquotes `` for command substitution in POSIX-compliant shells. I don't have experience with them. More info:

http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_03

So, if this applies to your shell, you can (should?) use:

parent=$(dirname $PWD)

grandparent=$(dirname $parent)

This should work in POSIX shells:

echo ${PWD%/*/*}

which will give you an absolute path rather than a relative one.

Also, see my answer here where I give two functions:

cdn () { pushd .; for ((i=1; i<=$1; i++)); do cd ..; done; pwd; }

which goes up n levels given n as an argument.

And:

cdu () { cd "${PWD%/$1/*}/$1"; }

which goes up to a named subdirectory above the current working directory.

why not use

"${PWD}/../.."

?

Not sed or regex, but this does do arbitrary parent quantity:

$ cd $(mktemp -dp $(mktemp -dp $(mktemp -dp $(mktemp -d)))) && 

> n=3 && 

> readlink -f  ${PWD}/$(for i in $(seq ${n}); do echo -n '../' ; done)

/tmp/tmp.epGcUeLV9q

In this example, I cd into a 5-deep temporary directory, assign n=3, construct a relative path n levels up from ${PWD}, and -f, --canonicalize the result with readlink.

Here's the regex that works for me. It's a little different between grep and Perl/sed:

The extended regex breaks up paths into 0 or more groups of /ABC123 anchored to the end of line, essentially working backward. (.*) consumes everything prior to this match and replaces it.

user@home:~/adir/bdir$ pwd

/home/user/adir/bdir



user@home:~/adir/bdir$ pwd | perl -pe 's|(.*)((/.*?){0})$|1|'

/home/user/adir/bdir



user@home:~/adir/bdir$ pwd | perl -pe 's|(.*)((/.*?){1})$|1|'

/home/user/adir



user@home:~/adir/bdir$ pwd | sed -r 's|(.*)((/.*?){2})$|1|'

/home/user



user@home:~/adir/bdir$ pwd | sed -r 's|(.*)((/.*?){3})$|1|'

/home



user@home:~/adir/bdir$ pwd | sed -r 's|(.*)((/.*?){4})$|1|'

Grep can simulate substitution using a positive look ahead (?= which tells grep to match everything except the pattern. -Po tells grep to use Perl regex and show only the match.

user@home:~/adir/bdir$ pwd

/home/user/adir/bdir



user@home:~/adir/bdir$ pwd | grep -Po '(.*)(?=((/.*?){0})$)'

/home/user/adir/bdir



user@home:~/adir/bdir$ pwd | grep -Po '(.*)(?=((/.*?){1})$)'

/home/user/adir



user@home:~/adir/bdir$ pwd | grep -Po '(.*)(?=((/.*?){2})$)'

/home/user



user@home:~/adir/bdir$ pwd | grep -Po '(.*)(?=((/.*?){3})$)'

/home



user@home:~/adir/bdir$ pwd | grep -Po '(.*)(?=((/.*?){4})$)'

Of course it works equally well for Windows style paths:

C:homeuseradirbdir> cd

C:homeuseradirbdir



C:homeuseradirbdir> cd | perl -pe 's|(.*)((\.*?){0})$|1|'

C:homeuseradirbdir



C:homeuseradirbdir> cd | sed -r 's|(.*)((\.*?){1})$|1|'

C:homeuseradir



C:homeuseradirbdir> cd | grep -Po '(.*)(?=((\.*?){2})$)'

C:homeuser



C:homeuseradirbdir> cd | grep -Po '(.*)(?=((\.*?){3})$)'

C:home



C:homeuseradirbdir> cd | grep -Po '(.*)(?=((\.*?){4})$)'

C:

Sorry for the edits but I've been working on this enigma for about 16 hours now. Just kept trying different permutations and re-reading the regex docs. It had to sink in eventually.