Timeline for What are the shell's control and redirection operators?
Current License: CC BY-SA 4.0
40 events
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| Mar 15, 2023 at 11:53 | comment | added | Imran |
When you're using &, you should be aware that ctrl + c only stops last command, other commands run in the background and you've to manually find and kill the processes.
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| Sep 30, 2021 at 13:13 | history | edited | ilkkachu | CC BY-SA 4.0 |
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| Jun 24, 2020 at 16:13 | comment | added | terdon♦ |
@felwithe essentially, yes. In fact, you very rarely (if ever) need cat file | command, this is a classic example of UUoC (useless use of cat).
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| Jun 24, 2020 at 15:54 | comment | added | felwithe |
So command < file.txt is the same as cat file.txt | command?
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| Jun 6, 2020 at 16:16 | history | rollback | terdon♦ |
Rollback to Revision 18
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| Jun 6, 2020 at 16:03 | history | rollback | terdon♦ |
Rollback to Revision 16
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| Jun 6, 2020 at 16:01 | history | edited | user232326 | CC BY-SA 4.0 |
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| Jun 6, 2020 at 15:38 | history | edited | user232326 | CC BY-SA 4.0 |
Extended description of `>&` and `&>` redirection.
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| Jun 3, 2020 at 19:07 | history | edited | Gilles 'SO- stop being evil' | CC BY-SA 4.0 |
https://unix.stackexchange.com/questions/590694/posix-compliant-way-to-redirect-stdout-and-stderr-to-a-file
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| Jun 25, 2019 at 20:03 | history | edited | user232326 | CC BY-SA 4.0 |
Correct `!` description. Links to operators (redirection and control) reference in the posix spec.
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| Mar 8, 2019 at 4:40 | comment | added | Stilez |
Can this excellent answer be edited to clarify one small aspect of redirects: Is there actually any difference between cmd1 | cmd2 and cmd2 < $( cmd1 )? Why are there two ways, syntactically, to direct stdin from one process to another, and when do shell scripts tend to use one or the other? Are there any commonly-encountered limitations in other usual syntax + operators one can use, or any common confusions, caused by the "<" appearing after the command it's directing into?
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| May 22, 2018 at 19:12 | comment | added | Amit Naidu |
There's also the >! analogue of >| to be aware of, in some non-bash shells.
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| Dec 11, 2017 at 22:06 | comment | added | G-Man Says 'Reinstate Monica' |
It should be noted that these symbols lose their special meaning and become ordinary textual characters when they are quoted (with '…' or "…") or escaped (with \); e.g., echo 'Tom & Jerry' or grep \< prog.c. Bash, specifically, also supports a $'…' syntax. These quoting methods — '…' and "…" (and $'…') — differ in ways that are discussed elsewhere.
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| Sep 15, 2017 at 14:54 | comment | added | terdon♦ |
@Arc676 No, they don't evaluate to true or false, that's a completely different context. This just means that an exit value of non-0 indicates a problem (not false) and an exit code of 0 indicates success (not true). That's always been the way and is quite standard. A non-0 exit code indicates an error in every environment I know of.
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| Sep 15, 2017 at 14:42 | comment | added | Arc676 |
The && and || uses seem counterintuitive. Doesn't this mean that exit code 0 evaluates to True and non-zero evaluates to False?
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| May 23, 2017 at 12:40 | history | edited | CommunityBot |
replaced http://stackoverflow.com/ with https://stackoverflow.com/
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| Apr 13, 2017 at 12:37 | history | edited | CommunityBot |
replaced http://unix.stackexchange.com/ with https://unix.stackexchange.com/
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| S Mar 19, 2017 at 16:02 | history | suggested | Moshe | CC BY-SA 3.0 |
fix var to foo
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| Mar 19, 2017 at 15:27 | review | Suggested edits | |||
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| Aug 4, 2016 at 11:08 | history | edited | cas | CC BY-SA 3.0 |
added info about piping from herenow docs
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| Dec 22, 2015 at 13:15 | history | edited | Stéphane Chazelas | CC BY-SA 3.0 |
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| Jun 25, 2015 at 11:32 | history | edited | Stéphane Chazelas | CC BY-SA 3.0 |
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| May 4, 2015 at 14:17 | vote | accept | terdon♦ | ||
| Mar 11, 2015 at 7:29 | comment | added | mikeserv | @hildred - I dunno. Maybe I was just trying to be thorough...? More likely it was a typo. Sorry to disappoint... | |
| Mar 11, 2015 at 5:06 | comment | added | hildred | @mikeserv >>> ? what does that do? where can I find out more about it? I know that you are not talking about >> which is standard. | |
| Nov 29, 2014 at 16:48 | history | edited | Stéphane Chazelas | CC BY-SA 3.0 |
There's no `>>(:)` just `>` redirection to a `>(...)` process substitution.
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| Nov 22, 2014 at 15:45 | history | edited | terdon♦ | CC BY-SA 3.0 |
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| Nov 4, 2014 at 14:50 | history | edited | Kimmax | CC BY-SA 3.0 |
corrected 2x "command1" where "command" should stand
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| Oct 6, 2014 at 23:33 | history | edited | mikeserv | CC BY-SA 3.0 |
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| Oct 6, 2014 at 20:11 | history | edited | Gilles 'SO- stop being evil' | CC BY-SA 3.0 |
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| Oct 6, 2014 at 20:02 | history | edited | Gilles 'SO- stop being evil' | CC BY-SA 3.0 |
indicate which operators are available only in some shells; group the sentence punctuation operators; link to my well-appreciated answer on brackets; show equivalences of && and ||; mention !; mention >|; mention process substitution
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| Oct 6, 2014 at 19:07 | history | made wiki | Post Made Community Wiki by terdon♦ | ||
| Oct 6, 2014 at 4:52 | comment | added | user44370 | This may help with the comparative angle. | |
| Oct 6, 2014 at 3:29 | comment | added | mikeserv | And ksh93, yash, mksh, and many others. But they will all likely operate slightly differently in edge-cases between shells - thats why these types of things are iffy. | |
| Oct 6, 2014 at 3:26 | comment | added | terdon♦ | @mikeserv thanks. They work on bash and zsh though. I don't know what, if anything, is truly bash-specific in that list. I should go through this and add the shells each works in but that would involve finding out first. | |
| Oct 6, 2014 at 3:23 | comment | added | mikeserv |
&>, >>>, and <<< are all non-posix as is the reference to not-only non-alphanum chars in a here-doc's name. This answer also discusses very little about how they work - for example, it is almost worse than useless to talk about a simple command and a command without explaining what these are and how the shell decides.
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| Oct 6, 2014 at 2:51 | comment | added | terdon♦ |
@GregHewgill yeah, I weaseled out of it by saying that I am discussing with respect to bash. This is being groomed as a canonical Q&A to close the various "What does this weird thingy do" questions and most of them are from users of bash. I'm hoping someone else will pitch in and answer for non bash shells, but highlighting the bash-specific ones makes a lot of sense. I'll have to check though, I don't know which they are off the top of my head.
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| Oct 6, 2014 at 2:34 | comment | added | Greg Hewgill | It would probably be worthwhile noting that not all shells are equal, and specifically highlighting the bash-specific features. | |
| Oct 6, 2014 at 2:25 | history | edited | terdon♦ | CC BY-SA 3.0 |
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| Oct 6, 2014 at 2:18 | history | answered | terdon♦ | CC BY-SA 3.0 |