CODEWITHSUNDEEP
bashshellsedhexascii
Ulrik
Ulrik

Reputation: 1141

Use sed te extract ascii hex string from a single line in a file

I have a file that looks like this:

some random
text
00ab46f891c2emore random
text
234324fc234ba253069
and yet more text

only one line in the file contains only hex characters (234324fc234ba253069), how do I extract that? I tried sed -ne 's/^\([a-f0-9]*\)$/\1/p' file I used line start and line end (^ and &) as delimiters, but I am obviously missing something...

Upvotes: 0

Views: 2835

Answers (3)

Avinash Raj
Avinash Raj

Reputation: 174696

Grep does the job,

$ grep '^[a-f0-9]\+$' file
234324fc234ba253069

Through awk,

$ awk '/^[a-f0-9]+$/{print}' file
234324fc234ba253069

Based on the search pattern given, awk and grep prints the matched line.

^             # start
[a-f0-9]\+    # hex characters without capital A-F one or more times
$             # End

Upvotes: 2

fedorqui
fedorqui

Reputation: 289495

sed can make it:

sed -n '/^[a-f0-9]*$/p' file
234324fc234ba253069

By the way, your command sed -ne 's/^\([a-f0-9]*\)$/\1/p' file is working to me. Note, also, that it is not necessary to use \1 to print back. It is handy in many cases, but now it is too much because you want to print the whole line. Just sed -n '/pattern/p' does the job, as I indicate above.

As there is just one match in the whole file, you may want to exit once it is found (thanks NeronLeVelu!):

sed -n '/^[a-f0-9]*$/{p;q}' file

Another approach is to let printf decide when the line is hexadecimal:

while read line
do
    printf "%f\n" "0x"$line >/dev/null 2>&1  && echo "$line"
done < file

Based on Hexadecimal To Decimal in Shell Script, printf "%f" 0xNUMBER executes successfully if the number is indeed hexadecimal. Otherwise, it returns an error. Hence, using printf ... >/dev/null 2>&1 && echo "$line" does not let printf print anything (redirects to /dev/null) but then prints the line if it was hexadecimal.

For your given file, it returns:

$ while read line; do printf "%f\n" "0x"$line >/dev/null 2>&1  && echo "$line"; done < a
234324fc234ba253069

Upvotes: 2

anubhava
anubhava

Reputation: 784868

Using egrep you can restrict your regex to select lines that only match valid hex characters i.e. [a-fA-F0-9]:

egrep '^[a-fA-F0-9]+$' file
234324fc234ba253069

Upvotes: 1

Related Questions