Re: echo $'\0' >a does not write the nul byte
Hello Ilkka, hello *! > Bash's echo is a builtin, so using it doesn't involve an execve(). Sure – but while passing a string (however it will be encoded) containing a null byte to builtins would be possible in principle (as zsh shows) this would lead to a large bunch of problems, e.g. another incompatibility between the builtin and the external echo. Best regards Martin
Re: echo $'\0' >a does not write the nul byte
Le 17/01/2021 à 22:02, Chet Ramey écrivait : On 1/17/21 3:05 PM, h...@artax.karlin.mff.cuni.cz wrote: Description: Command echo $'\0' |od -c writes 000 \n 001 in contrast to echo $'\1' |od -c 000 001 \n 002 The nul byte is not echoed by $'\0'. Repeat-By: echo $'\0' |od -c echo $'\1' |od -c Shell builtin commands obey the same argv conventions as any other Unix program: arguments are null-terminated strings. That means that echo $'\0' echo '' echo "" are all equivalent, and none of them will output a null byte. The only way to output a null byte with shell built-in is: printf '\0' or non portable: echo -ne '\0' This is because `\0' is not a null byte or a nulll string but interpreted internally to the command to print a null byte. -- Léa Gris
Re: echo $'\0' >a does not write the nul byte
On Mon, Jan 18, 2021 at 12:02 AM Martin Schulte wrote: > To be exact, this is already caused by a Unix Kernel - strings passed by > the exex* system calls are null terminated, too. As it is the default in > the C programming language. Thus you can't pass a null byte in an argument > when invoking a program. > Bash's echo is a builtin, so using it doesn't involve an execve(). Most shells still don't allow passing NULs to builtins. Zsh is the exception, it does allow NUL bytes in internal variables and in arguments to builtins. But, that's Zsh, and of course even it can't pass the NUL as an argument to an external program, exactly because of the execve() interface.
Re: echo $'\0' >a does not write the nul byte
On 1/17/21 3:05 PM, h...@artax.karlin.mff.cuni.cz wrote: Description: Command echo $'\0' |od -c writes 000 \n 001 in contrast to echo $'\1' |od -c 000 001 \n 002 The nul byte is not echoed by $'\0'. Repeat-By: echo $'\0' |od -c echo $'\1' |od -c Shell builtin commands obey the same argv conventions as any other Unix program: arguments are null-terminated strings. That means that echo $'\0' echo '' echo "" are all equivalent, and none of them will output a null byte. -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, UTech, CWRUc...@case.eduhttp://tiswww.cwru.edu/~chet/
Re: echo $'\0' >a does not write the nul byte
Hello Hans, hello Eduardo! > On Sun, Jan 17, 2021 at 12:05 PM wrote: > > (...) > > The nul byte is not echoed by $'\0'. > > This is expected. Bash uses NUL-byte terminated character sequences to > store strings, so it can't actually store NUL bytes themselves. To be exact, this is already caused by a Unix Kernel - strings passed by the exex* system calls are null terminated, too. As it is the default in the C programming language. Thus you can't pass a null byte in an argument when invoking a program. Best regards Martin
echo $'\0' >a does not write the nul byte
Configuration Information [Automatically generated, do not change]: Machine: x86_64 OS: linux-gnu Compiler: gcc Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H -I. -I../bash -I../bash/include -I../bash/lib -D_FORTIFY_SOURCE=2 -g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall uname output: Linux artax 3.2.0-4-amd64 #1 SMP Debian 3.2.96-2 x86_64 GNU/Linux Machine Type: x86_64-pc-linux-gnu Bash Version: 4.2 Patch Level: 37 Release Status: release Description: Command echo $'\0' |od -c writes 000 \n 001 in contrast to echo $'\1' |od -c 000 001 \n 002 The nul byte is not echoed by $'\0'. Repeat-By: echo $'\0' |od -c echo $'\1' |od -c
Re: echo $'\0' >a does not write the nul byte
On Sun, Jan 17, 2021 at 12:05 PM wrote: > (...) > The nul byte is not echoed by $'\0'. This is expected. Bash uses NUL-byte terminated character sequences to store strings, so it can't actually store NUL bytes themselves. $'\0' is the same as '' (i.e. an empty string). If you want to output an actual NUL byte, try using: printf '\0' Instead
