Re: [linux] expansion of tilde for home directory
On Thu, 17 Jun 2021 11:35:19 -0400 jean-Francois Messier wrote: > I would also assume that if this command was run as root it would not > work, as root's home directory is /root. DIR="$(echo ~)/Something/" would "fix" that, but... ... this is why you should not use shell programming for anything serious or production-level, IMO. Its quoting rules are traps for the unwary. Better to use a proper language like Python, Perl or whatever. Regards, Dianne. To unsubscribe send a blank message to linux+unsubscr...@linux-ottawa.org To get help send a blank message to linux+h...@linux-ottawa.org To visit the archives: https://lists.linux-ottawa.org
Re: [linux] expansion of tilde for home directory
On Thu 2021-06-17 14:26:01 -0400, Alex Pilon wrote: > On Thu 2021-06-17 13:43:43 -0400, Ian! D. Allen wrote: > > As others have said, quoting (even double quoting) hides tilde expansion. > > Just make sure the tilde isn't inside quotes and it works fine: > > > > DIR=~/"Something" > > Strictly speaking per spec this won't work. Tilde expansion happens > before parameter substitution. If it happens in any other order, that is > undefined behaviour and a portability issue. I misread that. That's my fault. I was thinking of some other thread when referring to other users. Ian's right. Apologies for the spam list. To unsubscribe send a blank message to linux+unsubscr...@linux-ottawa.org To get help send a blank message to linux+h...@linux-ottawa.org To visit the archives: https://lists.linux-ottawa.org
Re: [linux] expansion of tilde for home directory
On Thu 2021-06-17 13:43:43 -0400, Ian! D. Allen wrote: > As others have said, quoting (even double quoting) hides tilde expansion. > Just make sure the tilde isn't inside quotes and it works fine: > > DIR=~/"Something" Strictly speaking per spec this won't work. Tilde expansion happens before parameter substitution. If it happens in any other order, that is undefined behaviour and a portability issue. So § 2.6 ¶ 2 of the 2018 rev of the spec. https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06 > > Heck, I'd just if [ -d ~/Something ]; then > > No, not if "Something" is text or a variable that could include spaces > or GLOB characters. Always double-quote your variables. This is a literal. We all know what we are doing for space-less literals. I would never imply otherwise for variables. It's in my company policy, that I wrote, that there will be no exceptions even if you know that the inputs are always safe, and it's there because humans consistently make mistakes at least some times (or all the time for juniors developers who learned shell script chaotically or haphazardly). > None of the above is needed if you only want the HOME directory of the > person running the script. All that work is already done for you and > sitting in your $HOME environment variable. The one line: > > DIR="$HOME/Something" > > Works for any user, even root, even on old shells that don't expand > tildes, even if $HOME or Something contains blanks or GLOB characters. I'm pretty sure that JFM meant that it doesn't look up the home of the original user if you ran it under sudo (and expect nothing from su or other). That'd be $SUDO_USER then, though it's only 40 more characters to command sub then cut -d : -f …, like I said in a private email. To unsubscribe send a blank message to linux+unsubscr...@linux-ottawa.org To get help send a blank message to linux+h...@linux-ottawa.org To visit the archives: https://lists.linux-ottawa.org
Re: [linux] expansion of tilde for home directory
> DIR="/home/$(basename ~)/Something/" As others have pointed out, it's the unquoted tilde in the command substitution that is expanding above. You could have used this (but don't): DIR="$(echo ~)/Something/" As others have said, quoting (even double quoting) hides tilde expansion. Just make sure the tilde isn't inside quotes and it works fine: DIR=~/"Something" > Heck, I'd just if [ -d ~/Something ]; then No, not if "Something" is text or a variable that could include spaces or GLOB characters. Always double-quote your variables. Since the tilde is exactly equivalent to $HOME, this is cleanest: DIR="$HOME/Something" if [ -d "$DIR" ] ; then ... > I would also assume that if this command was run as root it would not > work, as root's home directory is /root. Same for any other user whose > home directory is not under /home. Perhaps a few-lines script would > first have to grep the login ID from /etc/passwd (read-only, so OK), > parse the line to get the actual home directory and return it. None of the above is needed if you only want the HOME directory of the person running the script. All that work is already done for you and sitting in your $HOME environment variable. The one line: DIR="$HOME/Something" Works for any user, even root, even on old shells that don't expand tildes, even if $HOME or Something contains blanks or GLOB characters. *ALWAYS DOUBLE QUOTE YOUR VARIABLE EXPANSIONS* https://teaching.idallen.org/cst8207/19w/notes/320_shell_variables.html#double-quote-all-uses-of-variables -- | Ian! D. Allen, BA, MMath - idal...@idallen.ca - Ottawa, Ontario, Canada | Home: www.idallen.com Contact Improvisation Dance: www.contactimprov.ca | Former college professor (Free/Libre GNU+Linux) at: teaching.idallen.com | Defend digital freedom: http://eff.org/ and have fun: http://fools.ca/ To unsubscribe send a blank message to linux+unsubscr...@linux-ottawa.org To get help send a blank message to linux+h...@linux-ottawa.org To visit the archives: https://lists.linux-ottawa.org
Re: [linux] expansion of tilde for home directory
I would also assume that if this command was run as root it would not work, as root's home directory is /root. Same for any other user whose home directory is not under /home. Perhaps a few-lines script would first have to grep the login ID from /etc/passwd (read-only, so OK), parse the line to get the actual home directory and return it. On 2021-06-17 10:55 a.m., J C Nash wrote: > While I've found a workaround, I was a bit surprised that a test for > existence of > a directory in a bash script did not work. > > I tried > > DIR="~/Something/" > if [ -d "$DIR" ]; then > > and got that the directory did NOT exist when it was clearly there. > > Workaround was to use > > DIR="/home/$(basename ~)/Something/" > > I did a bit of a search, but found no mention of the fact that ~ is not > expanded in the if [ ] construct. Is it, in fact, "well-known" except > to me? > > Cheers, JN > > > > To unsubscribe send a blank message to linux+unsubscr...@linux-ottawa.org > To get help send a blank message to linux+h...@linux-ottawa.org > To visit the archives: https://lists.linux-ottawa.org > To unsubscribe send a blank message to linux+unsubscr...@linux-ottawa.org To get help send a blank message to linux+h...@linux-ottawa.org To visit the archives: https://lists.linux-ottawa.org
Re: [linux] expansion of tilde for home directory
On 2021-06-17 10:55 a.m., J C Nash wrote: DIR="~/Something/" if [ -d "$DIR" ]; then DIR=~/Something/ if [ -d "$DIR" ]; then or DIR=~/"Something with spaces/" if [ -d "$DIR" ]; then
Re: [linux] expansion of tilde for home directory
On Thu 2021-06-17 10:55:27 -0400, J C Nash wrote: > While I've found a workaround, I was a bit surprised that a test for > existence of > a directory in a bash script did not work. This is POSIX shell in general. > I tried > > DIR="~/Something/" Just DIR="$HOME/Something" unless you need to refer to someone else's home. > if [ -d "$DIR" ]; then Heck, I'd just if [ -d ~/Something ]; then > and got that the directory did NOT exist when it was clearly there. > > Workaround was to use > > DIR="/home/$(basename ~)/Something/" > > I did a bit of a search, but found no mention of the fact that ~ is not > expanded in the if [ ] construct. Is it, in fact, "well-known" except > to me? It's because the tilde is in quotes. See 2018 POSIX shell command language § 2.6.1 Tilde Expansion A "tilde-prefix" consists of an unquoted character at the beginning of a word, followed by all of the characters preceding the first unquoted in the word, or all the characters in the word if there is no . https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_01 Your tilde in your command substitution is unquoted, which is why it works. To unsubscribe send a blank message to linux+unsubscr...@linux-ottawa.org To get help send a blank message to linux+h...@linux-ottawa.org To visit the archives: https://lists.linux-ottawa.org
[linux] expansion of tilde for home directory
While I've found a workaround, I was a bit surprised that a test for existence of a directory in a bash script did not work. I tried DIR="~/Something/" if [ -d "$DIR" ]; then and got that the directory did NOT exist when it was clearly there. Workaround was to use DIR="/home/$(basename ~)/Something/" I did a bit of a search, but found no mention of the fact that ~ is not expanded in the if [ ] construct. Is it, in fact, "well-known" except to me? Cheers, JN To unsubscribe send a blank message to linux+unsubscr...@linux-ottawa.org To get help send a blank message to linux+h...@linux-ottawa.org To visit the archives: https://lists.linux-ottawa.org
