sed - pass match to external command

Question

I have written a little script using sed to transform this:

kaefert@Ultrablech ~ $ cat /sys/class/power_supply/BAT0/uevent
POWER_SUPPLY_NAME=BAT0
POWER_SUPPLY_STATUS=Full
POWER_SUPPLY_PRESENT=1
POWER_SUPPLY_TECHNOLOGY=Li-ion
POWER_SUPPLY_CYCLE_COUNT=0
POWER_SUPPLY_VOLTAGE_MIN_DESIGN=7400000
POWER_SUPPLY_VOLTAGE_NOW=8370000
POWER_SUPPLY_POWER_NOW=0
POWER_SUPPLY_ENERGY_FULL_DESIGN=45640000
POWER_SUPPLY_ENERGY_FULL=44541000
POWER_SUPPLY_ENERGY_NOW=44541000
POWER_SUPPLY_MODEL_NAME=UX32-65
POWER_SUPPLY_MANUFACTURER=ASUSTeK
POWER_SUPPLY_SERIAL_NUMBER=

into a csv file format like this:

kaefert@Ultrablech ~ $ Documents/Asus\ Zenbook\ UX32VD/power_to_csv.sh 
"date";"status";"voltage µV";"power µW";"energy full µWh";"energy now µWh"
2012-07-30 11:29:01;"Full";8369000;0;44541000;44541000 
2012-07-30 11:29:02;"Full";8369000;0;44541000;44541000 
2012-07-30 11:29:04;"Full";8369000;0;44541000;44541000
... (in a loop)

What I would like now is to divide each of those numbers by 1.000.000 so that they don't represent µV but V and W instead of µW, so that they are easily interpretable on a quick glance. Of course I could do this manually afterwards once I've opened this csv inside libre office calc, but I would like to automatize it.

So what I found is, that I can call external programs in between sed, like this:

...
s/\nPOWER_SUPPLY_PRESENT=1\nPOWER_SUPPLY_TECHNOLOGY=Li-ion\nPOWER_SUPPLY_CYCLE_COUNT=0\nPOWER_SUPPLY_VOLTAGE_MIN_DESIGN=7400000\nPOWER_SUPPLY_VOLTAGE_NOW=\([0-9]\{1,\}\)/";'`echo 0`'\1/

and that I could get values like I want by something like this:

echo "scale=6;3094030/1000000" | bc | sed 's/0\{1,\}$//'

But the problem now is, how do I pass my match "\1" into the external command?

If you are interested in looking at the full script, you'll find it there: http://koega.no-ip.org/mediawiki/index.php/Battery_info_to_csv

I guess so: kaefert@Ultrablech ~ $ sed --version GNU sed version 4.2.1 — kaefert, Jul 30 '12 at 10:17

score 11 · Accepted Answer · answered Jul 30 '12 at 10:20

11

if your sed is GNU sed. you can use 'e' to pass matched group to external command/tools within sed command.

an example might be helpful to make it clear:

say, you have a problem:
you have a string "120+20foobar" now you want to get the calculation result of 120+20 part, and replace "oo" to "xx" in "foobar" part.

Note that this example is not for solving the problem above, just for showing the sed 'e' usage

so you could make 120+20 in the first match group, and rest in 2nd group, then pass two groups to different command/tools and then get the result. like:

   kent$  echo "100+20foobar"|sed -r 's#([0-9+]*)(.*)#echo  \1 \|bc\;echo \2 \| sed "s/oo/xx/g"#ge'
    120
    fxxbar

in this way, you could nest many seds one in another one, till you get lost. :D

answered Jul 30 '12 at 10:20

Kent

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thats exactly what I wanted! I tried to incoperate it into my script by adding this line: "s/$[0-9]\{1,\}$/echo \1/e" - but as soon as I add the "e" modifier at the end of this line, he tries to run earlier printed stuff that is surely not matched by this line as commands.. --> "sh: 1: Full: not found" – kaefert Jul 30 '12 at 10:50
okey, solved it. e is not as I first thought a modifier but a command on its own, that makes sed execute all the resulting text on the linux command line. SO I had to adapt everything so that that worked. If anyone want's to see the result, I've updates the script at http://kaefert.is-a-geek.org/mediawiki/index.php/Battery_info_to_csv – kaefert Jul 30 '12 at 11:40
@Sławosz there is a similar question with the same trick. I explained there. check this out: http://stackoverflow.com/questions/15454914 – Kent May 14 '13 at 14:29
Here is the archived link of user @kaefert: https://web.archive.org/web/20140414054655/https://kaefert.is-a-geek.org/mediawiki/index.php/Battery_info_to_csv – Serge Stroobandt Feb 09 '15 at 09:36

score 2 · Answer 2 · answered Jul 30 '12 at 10:08

2

As sed doesn't do arithmetic on its own I would recommend using awk for something like this, e.g. to divide 3rd, 5th and 6th field by a million do something like this:

 awk -F';' -v OFS=';' '
   NR == 1
   NR != 1 { 
     $3 /= 1e6
     $5 /= 1e6
     $6 /= 1e6
     print
   }'

Explanation

-F';' and -v OFS=';' specify the input and output field separator.
NR == 1 pass first line through without change.
NR != 1 if it is not the first line, divide and print.

answered Jul 30 '12 at 10:08

Thor

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thanks for the answer. the reason I did not do it that way is that I wanted to do everything in one step. With this method I would have needed to either rewrite everything, or to first do my sed stuff and use the output of sed as input for awk and then parse the csv with awk. would probably also have worked but since there is another way to do it directly with sed I used that one. – kaefert Jul 30 '12 at 13:07

alinsoar · Answer 3 · 2012-07-30T11:34:45.570

0

To divide by 1,000,000 directly, you do so :

Q='3094030/1000000'
sed ':r /^[[:digit:]]\{7\}/{s$\([[:digit:]]*\)\([[:digit:]]\{6\}\)/1000000$\1.\2$;p;d};s:^:0:;br;d'

edited Jul 30 '12 at 11:34

answered Jul 30 '12 at 10:09

alinsoar

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thats a nice idea! but the problem is that those numbers can also have less than 6 digits, in which case your solution would not match it – kaefert Jul 30 '12 at 10:27
I think I'm gonna go with Kent's answer, will accept it as soon as finished adapting my script in a way that it works again ;) – kaefert Jul 30 '12 at 11:11

sed - pass match to external command

3 Answers3

Explanation

Linked