converting bash output to JSON / Dictionary

Question

I am trying to create a JSON compatible output in bash that can be read by nodejs & python:

{"link":XX,"signal":YY,"noise":ZZ}

here's the unfiltered result:

iwconfig wlan0            
wlan0     IEEE 802.11bg  ESSID:"wifi@someplace"  Nickname:"<WIFI@REALTEK>"
          Mode:Managed  Frequency:2.452 GHz  Access Point: C8:4C:75:20:B4:8E   
          Bit Rate:54 Mb/s   Sensitivity:0/0  
          Retry:off   RTS thr:off   Fragment thr:off
          Encryption key:A022-1191-3A   Security mode:open
          Power Management:off
          Link Quality=100/100  Signal level=67/100  Noise level=0/100
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

But after applying my filters:

iwconfig wlan0 | grep Link | tr -d '/100' | tr '=' ' ' | xargs | awk '{printf "{\"link\":"$3",\"signal\":"$6",\"noise\":"$9"}"}'

I am getting erratic and incomplete results:

{"link":98,"signal":6,"noise":}
{"link":Signal,"signal":Noise,"noise":}

The "noise" value is never captured, and sometimes printf returns the wrong chunk.

Is there a more 'reliable' way of doing this ?

Thanks for all of the suggestions, but I really needed to fix my version of the code as I really struggle with REGEX and selected @Thrustmaster solution in the end. — crankshaft
– crankshaft, Commented Dec 17, 2013 at 0:34

UltraInstinct · Accepted Answer · 2013-12-16 09:14:53Z

1

The problem with the code in your question is here:

tr -d '/100'

What that command does it simply delete all the characters: '/', '1', '0'.

From the manual for tr,

  -d, --delete
      delete characters in SET1, do not translate

Thats not something you'd want. What you want is to replace the entire string /100 with "".

Use: sed 's/\/100//g' instead.

... | grep Link | sed 's/\/100//g' | tr '=' ' ' | awk '{printf "{\"link\":"$3",\"signal\":"$6",\"noise\":"$9"}"}'

answered Dec 16, 2013 at 9:14

UltraInstinct

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Sebastian Paaske Tørholm · Accepted Answer · 2013-12-16 09:10:45Z

0

You could restructure the output using perl, by piping the output through the following command:

perl -n -E 'if ($_ =~ qr{Link Quality=(\d+)/100.*?Signal level=(\d+)/100.*?Noise level=(\d+)/100}) { print qq({"link":$1,"signal":$2,"noise":$3}); }'

answered Dec 16, 2013 at 9:10

Sebastian Paaske Tørholm

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anubhava · Accepted Answer · 2013-12-16 09:14:31Z

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Using awk it is quite simple:

awk -F '[ =/]+' '$2=="Link"{printf "{\"%s\":%s,\"%s\":%s,\"%s\":%s}\n", 
                                   $2, $5, $6, $8, $10, $12}'
{"Link":100,"Signal":67,"Noise":0}

answered Dec 16, 2013 at 9:14

anubhava

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