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  • Since this question keeps on coming up, I thought I’d try my hand at writing a “canonical answer”. Should I post it here (and maybe link to it from some of the other more heavily trafficked questions), or should I move it to one of the questions that actually raises this issue? Also, is this perhaps a situation where questions should be merged? Commented Feb 21, 2015 at 20:43
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    /tmp A directory made available for applications that need a place to create temporary files. Applications shall be allowed to create files in this directory, but shall not assume that such files are preserved between invocations of the application. Commented Feb 21, 2015 at 22:05
  • @mikeserv: Yeah, (1) I'm quoting syntaxerror, and (2) I said I was surprised. I thought that, if anything would be read-write, it would be /tmp. Commented Feb 21, 2015 at 22:09
  • Well, the thing @syntaxerror said is doubly strange because, as I think, dash would be the default recovery shell on Ubuntu and it not only does not understand a <<< herestring, but it also gets anonymous pipes for << heredocuments and doesn't mess with ${TMPDIR:-/tmp} for that purpose at all. See this or this for demos on here-document handling. Also why the same amount of output or less warning? Commented Feb 21, 2015 at 22:15
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    @mikeserv: Well, the dd … conv=notrunc and the 1<> answers never truncate the output file, so, if the output of the command is less than the input (e.g., grep), there will be some bytes of the original left over at the end of the file. And, if the output is larger than the input (e.g., cat -n, nl, or (potentially) grep -n), there's a risk of overwriting old data before you've read it. Commented Feb 21, 2015 at 23:32