Why do I keep destroying my text files?

Question

I have destroyed a bunch of non-essential files and I don't know why. I have been executing commands like:

tr -sc 'A-Za-z' '\n' > somefile.txt | less

there is no output (blank page with flashing END) and upon checking all the content from the file is erased.

Another command that erased a full text file

grep someword > someotherfile.txt  | less

You may want to read [what is meant by connecting STDOUT and STDIN?](http://unix.stackexchange.com/questions/31334/31339#31339) — Gilles 'SO- stop being evil', Mar 10 '12 at 02:58

score 19 · Accepted Answer · answered Mar 10 '12 at 02:12

19

The > operator means "take the output of the command, truncate the named file, and then write the output of the command to that.

Reading that command line I guess you want <, which is "read standard input from this file, and feed it to the command" instead.

answered Mar 10 '12 at 02:12

Daniel Pittman

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this has to be the stupidest question on the site. thanks. – kuch nahi Mar 10 '12 at 02:13
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There is nothing wrong with not knowing things. Everyone starts out from zero. – Daniel Pittman Mar 10 '12 at 02:17
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“There is no shame in not knowing; the shame lies in not finding out.” -- Russian Proverb – Iain Holder Mar 10 '12 at 15:04
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Ooooh. I've never had the redirect operators explained in that way, comparatively. I've been a casual linux user for years (not full time, obviously), and never learned properly how to use the < operator. Now I know, and this answer is what did it. @kuchnahi, even the veterans and long-time users are learning new things, every day. Don't sweat it. :) – Harv Mar 12 '12 at 17:55
Still, surely it would make some sense to _read the documentation_ for the language features you use, no? – Lightness Races in Orbit Nov 25 '14 at 09:35

score 12 · Answer 2 · answered Mar 10 '12 at 06:42

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While you make yourself familiar with I/O redirection, you might find it "safer" to enable noclobber shell setting. This prevents unintentional clobbering of your files. See your shell man page and http://en.wikipedia.org/wiki/Clobbering

answered Mar 10 '12 at 06:42

Gowtham

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+1 great tip, and this is something I do, even with many years of experience. Typos happen, and this helps. – glenn jackman Mar 10 '12 at 14:34
I still have to think twice with < and >. Thanks for the tip. – stefgosselin Mar 15 '12 at 20:33

score 6 · Answer 3 · answered Mar 10 '12 at 02:13

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These commands have clobbered the text file because you told it to (> file will truncate any existing file before writing to it). You are probably looking for <, which means "redirect standard input from here".

answered Mar 10 '12 at 02:13

Chris Down

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Why do I keep destroying my text files?

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