CODEWITHSUNDEEP
stringbash
CIsForCookies
CIsForCookies

Reputation: 12807

hex to ascii in bash

I have a binary file containing ascii values and \000: its name is input and this is its hexdump (xxd -c 1):

0000000: 68  h
0000001: 65  e
0000002: 6c  l
0000003: 6c  l
0000004: 6f  o
0000005: 20
0000006: 00  .
0000007: 20
0000008: 77  w
0000009: 6f  o
000000a: 72  r
000000b: 6c  l
000000c: 64  d

I'm trying to create a script to parse this file, and yield the string up to the null byte.

this is my attempt so far:

buf=""
for x in $(xxd -p -c 1 input); do
    echo "x   = $x"
    if [ ${x} == 00 ]; then
        echo "break"
        break;
    else
        y=$(echo $x | xxd -r)
        echo "y   = $y"
        echo "buf = $buf"
        buf="$buf$y"
    fi
done
echo $buf

The output is:

x   = 68
y   =
buf =
x   = 65
y   =
buf =
x   = 6c
y   =
buf =
x   = 6c
y   =
buf =
x   = 6f
y   =
buf =
x   = 20
y   =
buf =
x   = 00
break

so at least I'm breaking the loop at the right time, but I don't understand why the assignment is not happening right

Upvotes: 1

Views: 2242

Answers (2)

CIsForCookies
CIsForCookies

Reputation: 12807

Ok, figured it out.

xxd -r expects 0x as a prefix to identify the hexadecimal number. This solved it for me: 

y=$(echo "0x$x" | xxd -r)

Though, I must admit this is weird, because I thought echo "a" | xxd -p | xxd -r should result in the original letter

Upvotes: 2

Maya
Maya

Reputation: 1527

There's a better solution! head supports NUL as a line delimiter. Try

head -zn1 input

In case you need other fields, try

head -zn7 input | tail -zn1

Upvotes: 0

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