问题
I've got a script that calls grep to process a text file. Currently I am doing something like this.
$ grep 'SomeRegEx' myfile.txt > myfile.txt.temp
$ mv myfile.txt.temp myfile.txt
I'm wondering if there is any way to do in-place processing, as in store the results to the same original file without having to create a temporary file and then replace the original with the temp file when processing is done.
Of course I welcome comments as to why this should or should not be done, but I'm mainly interested in whether it can be done. In this example I'm using grep, but I'm interested about Unix tools in general. Thanks!
回答1:
Perl has the -i switch, so does sed and Ruby
sed -i.bak -n '/SomeRegex/p' file
ruby -i.bak -ne 'print if /SomeRegex/' file
But note that all it ever does is creating "temp" files at the back end which you think you don't see, that's all.
Other ways, besides grep
awk
awk '/someRegex/' file > t && mv t file
bash
while read -r line;do case "$line" in *someregex*) echo "$line";;esac;done <file > t && mv t file
回答2:
sponge (in moreutils package in Debian/Ubuntu) reads input till EOF and writes it into file, so you can grep file and write it back to itself.
Like this:
grep 'pattern' file | sponge file
回答3:
In general, this can't be done. But Perl has the -i switch:
perl -i -ne 'print if /SomeRegEx/' myfile.txt
Writing -i.bak will cause the original to be saved in myfile.txt.bak.
(Of course internally, Perl just does basically what you're already doing -- there's no special magic involved.)
回答4:
No, in general it can't be done in Unix like this. You can only create/truncate (with >) or append to a file (with >>). Once truncated, the old contents would be lost.
回答5:
To edit file in-place using vim-way, try:
$ ex -s +'%!grep foo' -cxa myfile.txt
Alternatively use sed or gawk.
回答6:
Store in a variable and then assign it to the original file:
A=$(cat aux.log | grep 'Something') && echo "${A}" > aux.log
回答7:
Take a look at my slides "Field Guide To the Perl Command-Line Options" at http://petdance.com/perl/command-line-options.pdf for more ideas on what you can do in place with Perl.
回答8:
Most installations of sed can do in-place editing, check the man page, you probably want the -i flag.
来源：https://stackoverflow.com/questions/3979548/in-place-processing-with-grep