GNU bug report logs - #47281
sed: problem with hex replace a literal '$'

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Bastian Bittorf <bb <at> npl.de>
To: bug-sed <at> gnu.org
Subject: sed: problem with hex replace a literal '$'
Date: Sat, 20 Mar 2021 09:56:43 +0000

Dear hard working developers,

when replacing in hex mode, and a '$' = \x24 is at
the end of the search string, it seems to be parsed
as 'end', which was at least not intended by my usage:

e.g.
# echo 'foo $bar$ baz' >testfile

# hexdump -C testfile
00000000  66 6f 6f 20 24 62 61 72  24 20 62 61 7a 0a        |foo $bar$ baz.|
#                     ^^^^^^^^^^^^^^^

# i want to replace '$bar$'
# sed 's/\x24\x62\x61\x72\x24/\x65\x65\x65\x65\x65/' testfile
foo $bar$ baz

(no match/replacement happens)

# now omit the last char '$'
# sed 's/\x24\x62\x61\x72/\x61\x65\x65\x65/' testfile
foo aeee$ baz

# now making the match on char longer:
# sed 's/\x24\x62\x61\x72\x24\x20/\x61\x65\x65\x65\x65\x20/' testfile
foo aeeee baz

# this happends with latest trunk/master:
# bastian <at> ryzen:~/software/sed$ sed/sed --version
sed/sed (GNU sed) 4.8.7-b352-dirty

I stumpled over this behaviour while
replacing real binary data, where randomly
a 0x24 was involved at the end of the match string

Thanks for reading and maybe fixing 8-)

bye, bastian

Message #8 received at 47281 <at> debbugs.gnu.org (full text, mbox):

From: Nora Platiel <nplatiel <at> gmx.us>
To: 47281 <at> debbugs.gnu.org
Subject: bug#47281: sed: problem with hex replace a literal '$'
Date: Sat, 20 Mar 2021 18:06:05 +0100

Hello,
the behavior you are describing is documented here:
https://www.gnu.org/software/sed/manual/sed.html#Escaping-Precedence
If you want to produce a basic regular expression given a string to be matched literally, precede any of $*.[\]^ with \
Likewise, if you are using hex escapes (\xHH), precede any of \x24 \x2a \x2e \x5b \x5c \x5d \x5e with \x5c

Message #11 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Bastian Bittorf <bb <at> npl.de>
To: bug-sed <at> gnu.org
Cc: nplatiel <at> gmx.us
Subject: bug#47281: sed: problem with hex replace a literal '$'
Date: Sun, 21 Mar 2021 14:53:58 +0000

> Hello,
>
> the behavior you are describing is documented here:
> https://www.gnu.org/software/sed/manual/sed.html#Escaping-Precedence
>
> If you want to produce a basic regular
> expression given a string to be matched 
> literally, precede any of $*.[\]^ with \
> Likewise, if you are using hex escapes (\xHH),
> precede any of \x24 \x2a \x2e \x5b \x5c \x5d \x5e with \x5c

Hi Nora,

thanks for your help suggesting the escaping.

I understand, that this behaviour is valid and not a bug.
Maybe you can post this to the Mailingslist as well,
i'am not subscribed there.

Indeed this is really awkward, but I have to
accept that and use now something like that:

#!/bin/sh
#
# [...]
#
# case "$hex" in
#   24|2a|2e|5b|5c|5d|5e)
#     hex="5c\x$hex"
#   ;;
# esac

see:
https://github.com/bittorf/kritis-linux/commit/d3cc6c84a6c021ae2f7e9351f9f4ef0fc7098c0b

Thanks again & bye,
Bastian Bittorf

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