I have a question and wondering how to address it with sed? How does one cut a variable up to a specific location, in my case _g?
variable="This_is_good_g0r0s0_continues"
I need to cut this variable up to _g. I should also mention, the number of characters before _g is random.
You can do that with internal variable expansion operators in all POSIX shells :
variable="This_is_good_g0r0s0_continues"
up_to_first__g="${variable%%_g*}"
up_to_last__g="${variable%_g*}"
export foo="$bar").
– Gilles 'SO- stop being evil'
Dec 04 '14 at 01:27
If you want to cut at last _g then try the following:
$ sed 's/\(.*\)_g.*/\1/' <<< 'This_is_good_g0r0s0_continues'
This_is_good
If you want to cut at first _g then
$ sed 's/_g.*//' <<< 'This_is_good_g0r0s0_continues'
This_is
With a BRE - with sed - you can slice match sequences by counting their occurrence. I do not think that sed would be an ideal tool for slicing shell var values - the shell provides a fairly intuitive means of doing that already - but that is already covered.
BRE pattern sequences when multiplied will split to the right as far as they might. For example:
echo 0123456789 | sed 's/\([0-9]\)*/\1/'
...prints 9. It gets a little more useful when you split with actual counts though.
Another example:
echo _good _goroso _goes _gop |
sed 's/\(.*_g\)\{2\}/\1/'
...which gets...
oes _gop
This wont work like you might think, though - or at least it doesn't work like I expected when I started playing with it. You can't go back another _g there with \{3\} - not in this case anyway. The pattern is too variable .* matches everything - including nothing - and it is therefore difficult to easily quantify. What you can do is continue to split it:
echo _good _goroso _goes _gop |
sed 's/\(\(.*_g\)\{2\}\)\{2\}/\1/'
...which prints
oroso _goes _gop
Perhaps it is better to say squeeze than it is split. Here - by matching at least so many occurrences of a .* zero-or-more occurrence pattern I effectively limit its possible match - which will always be as greedy as it might. So I slice smallest piece by smallest piece off of the end of what it matches.
This is more easily seen by looking at the match itself - which can still be had in & in addition to the match that is had already in \1. I've often found such eccentricities useful, personally, though i wouldn't be surprised to learn I am alone in that. You might, for example, compound the match from each end like:
echo _good _goroso _goes _gop |
sed 's/\(\(.*_g\)\{2\}\)\{2\}/&\1/
...which prints :
_good _goroso _goes _goroso _goes _gop
...because the entire match for .*_g is in & but the subdivided pattern is only a portion.
...or even...
echo _good _goroso _goes _gop |
sed 's/\(\(.*_g\)\{2\}\)\{2\}/\2&\1/
...which shuffles every level of the match like...
oes _g_good _goroso _goes _goroso _goes _gop
