Busybox hexdump bug

[MochiMoppel]

Hexdump can convert control characters into their backslash equivalents but there seems to be a problem with the form feed character (hex 0C)

Below example pipes a string of 3 characters to hexdump: backspace (x08) newline (x0a) and form feed (x0c)

Hexdump's "%_u" format translates this string correctly to bs lf and ff
However the "%_c" format translates it to \b \n and \b
And that's wrong. The backslash escape sequence of form feed is \f and not \b
My BusyBox version v1.21.0. may be too old. Has this been corrected? Does this bug exist in the full version (which I don't have)?

Code: Select all

#!/bin/bash
echo -en "\x08\x0A\x0C" | hexdump  -e '1 "%_u\n"'
echo
echo -en "\x08\x0A\x0C" | hexdump  -e '1 "%_c\n"'

[fredx181]

Hi mochimoppel, on Ubuntu Bionic, busybox version 1.27.2, it is correct:

Code: Select all

root@live64:~# echo -en "\x08\x0A\x0C" | busybox hexdump  -e '1 "%_c\n"'
\b
\n
\f

On Debian Stretch, busybox version 1.22.1, it's incorrect, same as your output.

Fred

[misko_2083]

busybox 1.22.1 busybox hexdump: b

Code: Select all

echo -en "\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0A\x0B\x0C\x0D" | busybox hexdump  -e '1 "%_c\n"' 
\0
001
002
003
004
005
006
\a
\b
\t
\n
\v
\b
\r

busybox 1.22.1 busybox od: f

Code: Select all

echo -en "\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0A\x0B\x0C\x0D" | busybox od -An -tc -w1 | sed -e 's/^[ \t]*//'
\0
001
002
003
004
005
006
\a
\b
\t
\n
\v
\f
\r

[drunkjedi]

Hexdump can convert control characters into their backslash equivalents but there seems to be a problem with the form feed character (hex 0C)

Below example pipes a string of 3 characters to hexdump: backspace (x08) newline (x0a) and form feed (x0c)

Hexdump's "%_u" format translates this string correctly to bs lf and ff
However the "%_c" format translates it to \b \n and \b
And that's wrong. The backslash escape sequence of form feed is \f and not \b
My BusyBox version v1.21.0. may be too old. Has this been corrected? Does this bug exist in the full version (which I don't have)?

Code: Select all

#!/bin/bash
echo -en "\x08\x0A\x0C" | hexdump  -e '1 "%_u\n"'
echo
echo -en "\x08\x0A\x0C" | hexdump  -e '1 "%_c\n"'

In fatdog64 both hexdump are present, busybox version is different from your's though.

Code: Select all

# whereis hexdump
hexdump: /usr/bin/hexdump /bin/hexdump /usr/share/man/man1/hexdump.1
#
# /usr/bin/hexdump -V
hexdump from util-linux 2.25.2
#
# /bin/hexdump --help
BusyBox v1.27.0.git (2017-11-10 04:22:11 UTC) multi-call binary.

Usage: hexdump [-bcCdefnosvxR] [FILE]...

Display FILEs (or stdin) in a user specified format

	-b		1-byte octal display
	-c		1-byte character display
	-d		2-byte decimal display
	-o		2-byte octal display
	-x		2-byte hex display
	-C		hex+ASCII 16 bytes per line
	-v		Show all (no dup folding)
	-e FORMAT_STR	Example: '16/1 "%02x|""\n"'
	-f FORMAT_FILE
	-n LENGTH	Show only first LENGTH bytes
	-s OFFSET	Skip OFFSET bytes
	-R		Reverse of 'hexdump -Cv'
# 

So I ran your code with both hexdumps.

hexdump from util-linux 2.25.2 gives following results

Code: Select all

# echo -en "\x08\x0A\x0C" | /usr/bin/hexdump  -e '1 "%_u\n"' 
bs
lf
ff
# echo -en "\x08\x0A\x0C" | /usr/bin/hexdump  -e '1 "%_c\n"'
\b
\n
\f
#

hexdump from BusyBox v1.27.0 gives same output

Code: Select all

# echo -en "\x08\x0A\x0C" | /bin/hexdump  -e '1 "%_u\n"' 
bs
lf
ff
# echo -en "\x08\x0A\x0C" | /bin/hexdump  -e '1 "%_c\n"'
\b
\n
\f
#

Hope this helps.

[MochiMoppel]

Thanks everyone.

So versions 1.26.0 and newer seem to be OK.

hexdump: fix numerous bugs in handling of backslashes

Wait a second - numerous? What did I miss?