Extract hash from file name

Question

When archiving certain data we encode the archive's sha1 HASH within the file name so as to determine the integrity of the archive.

I am trying to find a way to automate the integrity check by extracting the HASH out of the file name:

echo myid123_2019-08-31_b7769c0e22c7f75b2935afad499852630ca83145.tar.xz | sed -n 's/^.*\([[:xdigit:]]{40}\).*$/\1/p'
echo myid123_2019-08-31_b7769c0e22c7f75b2935afad499852630ca83145.tar.xz | sed -n 's/^.([0-9a-fA-F]{40}).$/\1/p'

Both tests above return no results. Am I missing something?

I would prefer to test for the HASH explicitly, rather then by elimination or position as the filename format can vary. In any case the hash would be delimited by non-hash characters.

Follow-up:

Thanks for the help.

This is the final product I was looking to create:

function checkhash () { 
 for f in "$@"
  do 
   test -f $f || continue
   export HASH=$(echo ${f}| grep -o  '[0-9a-fA-F]\{32,128\}' )
   case $(echo -n ${HASH} | wc -c) in
    32)
       echo "${HASH} *${f}" | md5sum -c -
    ;;
    40)
       echo "${HASH} *${f}" | sha1sum -c -
    ;;
    56)
       echo "${HASH} *${f}" | sha224sum -c -
    ;;
    64)
       echo "${HASH} *${f}" | sha256sum -c -
    ;;
    96)
       echo "${HASH} *${f}" | sha384sum -c -
    ;;
    128)
       echo "${HASH} *${f}" | sha512sum -c -
    ;;
    *)
       echo "No Identified HASH found in filename: ${f}"
    ;;
   esac
 done
}

{40} isn't a quantifier in a sed basic regular expression - you'd need sed -n 's/^.*$[[:xdigit:]]\{40\}$.*$/\1/p' or sed -En 's/^.*([[:xdigit:]]{40}).*$/\1/p'. See Why does my regular expression work in X but not in Y? — steeldriver, Sep 01 '22 at 00:24

score 1 · Answer 1 · answered Sep 01 '22 at 00:35

1

Your examples suggest the hash string begins after the right-most underscore (_) character and ends before the left-most dot (.) character.

If you don't mind a two-step process, you can do it in bash like this:

file_name="myid123_2019-08-31_b7769c0e22c7f75b2935afad499852630ca83145.tar.xz"
name_hash="${file_name%%.*}"
hash="${name_hash##*_}"
echo "$hash"

produces

b7769c0e22c7f75b2935afad499852630ca83145

answered Sep 01 '22 at 00:35

Sotto Voce

4,131

Again, this is biased on testing for something other then the hash/digest. A hash is a fixed length, long-run sequence 32, 40, 56, 64, 96, or 128 characters (depending on the hash) consisting of hexadecimal case in-sensitive characters [0-9,a-f]. The only thing I can count on about the delimiter is that they will be non-hexadecimal characters. – Mark C Sep 01 '22 at 18:55

score 1 · Answer 2 · answered Sep 01 '22 at 06:22

1

Let me offer something in awk:

echo myid123_2019-08-31_b7769c0e22c7f75b2935afad499852630ca83145.tar.xz | awk -F'[_.]' '{print $3}'

answered Sep 01 '22 at 06:22

Romeo Ninov

17,484

The problem here is that the test fixes on the delimiters which cannot be relied upon. I need to test for the embedded HASH string in the file name. – Mark C Sep 01 '22 at 16:47
@MarkC, provide REAL example and we can help you extract the hash. – Romeo Ninov Sep 01 '22 at 17:00
1

You seem to have missed the point. I got there eventually. Thanks to everyone for their efforts. – Mark C Sep 01 '22 at 18:45

QuartzCristal · Answer 3 · 2022-09-01T03:03:33.863

0

Perhaps using grep would do a cleaner job:

$ a='myid123_2019-08-31_b7769c0e22c7f75b2935afad499852630ca83145.tar.xz'
$ echo "$a" | grep -o  '[0-9a-fA-F]{40}'
b7769c0e22c7f75b2935afad499852630ca83145

Please note that the {...} need quoting \{...\} in BRE.

edited Sep 01 '22 at 03:03

answered Sep 01 '22 at 02:57

QuartzCristal

2,023

THANKS. This one seems to do the job quite nicely and keeps the code simple. – Mark C Sep 01 '22 at 18:57

score 0 · Answer 4 · answered Sep 01 '22 at 07:00

0

Using sed

$ sed -E 's/([^_]*_){2}([^.]*).*/\2/' input_file
b7769c0e22c7f75b2935afad499852630ca83145

answered Sep 01 '22 at 07:00

sseLtaH

2,786

score 0 · Answer 5 · answered Sep 01 '22 at 09:05

0

echo "myid123_2019-08-31_b7769c0e22c7f75b2935afad499852630ca83145.tar.xz"|awk -F "_" '{gsub(/\..*/,"",$NF);print $NF}'

output

b7769c0e22c7f75b2935afad499852630ca83145

answered Sep 01 '22 at 09:05

Praveen Kumar BS

5,211

Extract hash from file name

5 Answers5