Re: Typo in Bash Reference Manual
Date:Sun, 29 Jun 2025 08:13:07 -0600 From:Stan Marsh Message-ID: | So, is this POSIX, or just a dash-extension? It is original Bourne Shell (from 7th edition Bell Labs Unix) and is (or should be) supported by every Bourne-compatible shell. It definitely is in POSIX. kre
Re: Typo in Bash Reference Manual
>"Note that a negative offset must be separated from the [non-following]
>colon by at least one space to avoid being confused with the ':-'
>expansion,' since a negative offset can exist immediately beside a
>subsequent colon.
>Wiley
Note, incidentally, that it is not strictly true that a negative offset has
to be preceded by a space. A zero will work as well. And I think that is
clearer. I.e., instead of:
# Print the last 2 characters of $HOME
$ echo ${HOME: -2}
You can do:
$ echo ${HOME:0-2}
Or even:
$ echo ${HOME:7-9}
=
Please do not send me replies to my posts on the list.
I always read the replies via the web archive, so CC'ing to me is unnecessary.
Note that they always end up in my Spam file anyway, so it is annoying to have
to
periodically clean that out.
Re: Typo in Bash Reference Manual
And here is another interesting thing inspired by this thread. I always thought the "colon-free" versions of the P.E. was a bash-ism, but experimentation shows that it works in "dash" as well. And "man dash" contains the following text: In the parameter expansions shown previously, use of the colon in the format re- sults in a test for a parameter that is unset or null; omission of the colon re- sults in a test for a parameter that is only unset. So, is this POSIX, or just a dash-extension? = Please do not send me replies to my posts on the list. I always read the replies via the web archive, so CC'ing to me is unnecessary. Note that they always end up in my Spam file anyway, so it is annoying to have to periodically clean that out.
Re: Typo in Bash Reference Manual
On Sun, Jun 29, 2025 at 21:51:52 +0700, Robert Elz wrote:
> Date:Sun, 29 Jun 2025 08:13:07 -0600
> From:Stan Marsh
> Message-ID:
>
> | So, is this POSIX, or just a dash-extension?
>
> It is original Bourne Shell (from 7th edition Bell Labs Unix)
> and is (or should be) supported by every Bourne-compatible shell.
>
> It definitely is in POSIX.
In fact, the colon-less forms ${var-word} and so on were the originals.
The colon variants ${var:-word} were added later, IIRC by ksh.
See
Re: Typo in Bash Reference Manual
On Sun, Jun 29, 2025 at 06:39:18 -0600, Stan Marsh wrote:
> Note, incidentally, that it is not strictly true that a negative offset has
> to be preceded by a space. A zero will work as well. And I think that is
> clearer. I.e., instead of:
>
> # Print the last 2 characters of $HOME
> $ echo ${HOME: -2}
>
> You can do:
>
> $ echo ${HOME:0-2}
Or ${HOME:(-2)} if you like.
Re: Typo in Bash Reference Manual
On Sun, Jun 29, 2025, at 11:41 AM, Greg Wooledge wrote:
> The colon variants ${var:-word} were added later, IIRC by ksh.
Looks like the System III shell released them first:
https://www.in-ulm.de/~mascheck/bourne/#system3
--
vq
