base 64 decoding in shell scripting

Question

For Example I have a file like as follows .

A,Y29tLz9hPTQ2JmM9NDQzNzgmczE9Q0,123  
B,FJNLTA2MjQyMDE3LVAmczI9ODQ3MDA,321

I want to print field1,field2(by base 64 decoding),field3

Output Required ::

A,result of base 64 decode,123
B,result of base 64 decode,321

can some one help me out in this ? with out while loop please provide me the solution ? — Jyothi Tulasi
– Jyothi Tulasi, Commented Dec 13, 2017 at 18:51
If your goal is performance -- ie. having a single base64-decoding process, rather than starting a subprocess per line -- that requires a whole different approach (probably one best implemented by using Python or another language with native base64 decoding rather than shell). — Charles Duffy
– Charles Duffy, Commented Dec 13, 2017 at 18:53
Post the code that you have tried so far. Also, if your instructor places special requirements on how you solve this problem, let us know about those requirements. — John1024
– John1024, Commented Dec 13, 2017 at 18:54
What you're asking for can't be done in shell alone, and the tools to achieve this vary by operating system. Include your work so far, and we'll help you debug it. — ghoti
– ghoti, Commented Dec 13, 2017 at 19:03

Alexander O'Mara · Accepted Answer · 2017-12-13 18:59:47Z

1

You can do this in a bash script with a few read commands and base64 -D:

#!/bin/bash

while read -r line
do
  IFS=',' read -r c1 c2 c3 <<< "$line"
  data="$(base64 -D <<< "$c2")"
  echo "$c1,$data,$c3"
done < "inputfile.txt"

Your one base64 strings has binary data in it though, so output may look funky due to control characters.

A,com/?a=46&c=44378&s1=,123
���KL
  �
�,321T  �̏N

edited Dec 13, 2017 at 18:59

answered Dec 13, 2017 at 18:56

Alexander O'Mara

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3 Comments

Charles Duffy Over a year ago

Note "without while loop" in the OP's first comment.

Charles Duffy Over a year ago

BTW, personally, I'd use IFS=, read -r first data rest rather than read -a -- with the code as it is you're discarding fourth columns and onward if they exist, whereas if you don't use read -a it'll just put all remaining columns into the last one.

Charles Duffy Over a year ago

I'd also suggest data=$(base64 -D <<<"${parts[1]}") in place of the pipeline -- heredocs aren't free either, but they're usually less expensive than a FIFO from a subshell running echo.

Kent · Accepted Answer · 2017-12-13 18:56:01Z

0

give this awk one-liner a try:

awk -F',' -v OFS=',' '"echo "$2" | base64" | getline $2' file

Test with your example:

kent$  cat f
A,Y29tLz9hPTQ2JmM9NDQzNzgmczE9Q0,123  
B,FJNLTA2MjQyMDE3LVAmczI9ODQ3MDA,321

kent$  awk -F',' -v OFS=',' '"echo "$2" | base64" | getline $2' f
A,WTI5dEx6OWhQVFEySm1NOU5EUXpOemdtY3pFOVEwCg==,123  
B,RkpOTFRBMk1qUXlNREUzTFZBbWN6STlPRFEzTURBCg==,321

answered Dec 13, 2017 at 18:56

Kent

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2 Comments

Charles Duffy Over a year ago

Hmm. It certainly meets the text of "without while loop", but absolutely violates the spirit (since it's running a separate base64 command per line of input).

Charles Duffy Over a year ago

...and we're vulnerable to shell injection attacks if we had $(touch /tmp/i-am-evil) in place of base64-encoded data.

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