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I have data as following :

enter image description here

What i need to get is the OS_NATIVE_NAME of a particular DEVICE.

I know one way is to print its column value using:

awk '{print $*col_num*}'

But the column number for this OS_NATIVE_NAME is not fixed. This is because, other fields like STATUS can have values different (could be multiple sometime), which is causing a problem of not having fixed column number for the OS_NATIVE_NAME, which is the required data for my tests.

How can i grep that particular column's content??

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  • Can you assume that the columns begin in fixed character positions, or does that have to be determined dynamically from the header line? Commented Sep 25, 2015 at 6:53
  • Columns format & order is fixed. Is that what you are asking? Commented Sep 25, 2015 at 6:54
  • Is the output tab delimited or space delimited? Commented Sep 25, 2015 at 6:58
  • space limited. I tried like this also. # vxdisk -e list | awk '{print $1"\t\t\t" $6}' DEVICE OS_NATIVE_NAME disk_0 invalid disk_1 invalid intel_ssd0_0 sdc So you can see here, i am getting different data from different columns. Commented Sep 25, 2015 at 6:59
  • BTW: Can you please add the example data as code blocks? With an image it's hard to do test cases. Commented Sep 25, 2015 at 7:20

3 Answers 3

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With awk:

awk 'NR==1{for(i=1;i<NF;i++){if($i=="OS_NATIVE_NAME"){s=index($0,$i); l=index($0,$(i+1))-s}}} $1=="disk_0"{print substr($0,s,l)}' file
  • NR==1 if it's the first line (the header line), NR is awks internal variable for the current line number being processed.
    • for(i=1;i<NF;i++) loop trough the fields. NF is awks internal variable for the number of fields in the current line.
    • $i=="OS_NATIVE_NAME" since, we're looping trough each field, check if the field value equals OS_NATIVE_NAME
    • s=index(...) find the position of the start of the field and save it for later. index() is awks string function to get the position of the occurence of a string (here the value of $i, hence OS_NATIVE_NAME) in another string (here $0, hence the whole line).
    • l=index(...)-s get the length of the field and save it for later: same priciple as before, but to get the length we must substract s from it.
  • $1=="disk_0" find the DEVICE you are searching in the first field (disk_0 in the example). $1 represents the first field.
    • {print substr($0,s,l)} finally print for each line, the string started at position s, with length l. substr() is awks string function to cut a string (here $0; the whole line) from position s with length l (the two varibale we prevously extracted while processing line 1)

Prints (regardless of where the field is in the input):

sda
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  • I thought this but this will not work all the time, because position of OS_NATIVE_NAME string is not same as that of its data. right?? Commented Sep 25, 2015 at 7:13
  • @AmitM I think I don't understand, can you give an example? Why should the position of OS_NATIVE_NAME not be the same as its data? Commented Sep 25, 2015 at 7:15
  • Its working (y) but i couldn't understand it completely. Commented Sep 25, 2015 at 7:26
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One easy solution:

data=$(vxdisk -e list) devices=$(sed 's/ .*//' <<< "$data") # I'm just guessing that the relevant column starts in column 80 os_native_name=$(cut -c80- <<< "$data") row=0 for dev in $devices; do let row++; if [[ "$dev" = disk_1 ]]; then break; fi; done # now we know our desired data is on the row'th line of os_native_name # you can retrieve it for instance with sed -n "$row p" <<< "$os_native_name"
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  • This isnt working.. Commented Sep 25, 2015 at 7:14
  • It worked in my tests, can you give more information? Commented Sep 25, 2015 at 7:15
  • Can you tell me how can i upload image here? Data is not getting pasted properly.. Commented Sep 25, 2015 at 7:18
  • You can't upload an image to comments. Commented Sep 25, 2015 at 7:19
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Try below command:

vmdisk -e list | awk 'NR==1 { for(i=1;i<=NF;i++) { ix[$i] = i } } NR>1 { print $ix["OS_NATIVE_NAME"] }'
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