Buffer in order to avoir mistakes with redirections that empty your files

buffer () { tty -s && return; tmp=$(mktemp); cat > "${tmp}"; if [ -n "$1" ] && ( ( [ -f "$1" ] && [ -w "$1" ] ) || ( ! [ -a "$1" ] && [ -w "$(dirname "$1")" ] ) ); then mv -f "${tmp}" "$1"; else echo "Can't write in \"$1\""; rm -f "${tmp}"; fi }
A common mistake in Bash is to write command-line where there's command a reading a file and whose result is redirected to that file. It can be easily avoided because of : 1) warnings "-bash: file.txt: cannot overwrite existing file" 2) options (often "-i") that let the command directly modify the file but I like to have that small function that does the trick by waiting for the first command to end before trying to write into the file. Lots of things could probably done in a better way, if you know one...
Sample Output
$ echo "zbc" > file.txt # write 'zbc' in file.txt
$ cat file.txt | sed "s/z/a/g" > file.txt # we want 'abc' in file.txt (I know that the "cat" is useless here but...)
$ cat file.txt # we have nothing in file.txt

$ echo "zbc" > file.txt # write 'zbc' in file.txt
$ cat file.txt | sed "s/z/a/g" | buffer file.txt # we want 'abc' in file.txt
$ cat file.txt # we have 'abc' in file.txt
abc

2
By: Josay
2009-07-27 20:21:15

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    zsh$ M-v
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  • the last person who posted used the most roundabout way to concatinate files, there's a reason there's a "conCATinate" command... Using this method, you also get to choose the order of the files, below another person just did *.txt > combined.txt which is fine but the order depends on the implementation of "cat" which is probably alphabetical order of filenames. Show Sample Output


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  • indenting all the files at a time, if the file has local variable for indentation style its even better. This one liner is not pretty but it does the job.


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What Others Think

holy !@#$
linuxrawkstar · 464 weeks ago
debian/ubuntu moreutils has "sponge" which does what I think you're getting at: sed '...' file | grep '...' | sponge file
eichin · 464 weeks ago
Perl can do that fine too, if we just want to use a replacement: echo "zbc" > file.txt perl -pi -e 's/z/a/g' file.txt cat text.txt abc
Blackbit · 463 weeks and 5 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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