问题
I have got a file file.txt witch has got these entries
NY
LA
SF
I ran the command tr '\n' ',' < file.txt and it successfully deleted all of the newline characters.
I need all of this output in the same file.txt file, so I redirected the output like this
tr '\n' ',' < file.txt > file.txt,
but It does not put anything in the file.txt and the resultant file is empty, Can anyone explain to me why the output of tr is getting lost due to redirection.
回答1:
because it opens the output file first which deletes what is in the file and then feels nothing into the tr command and back out into the empty file
tr '\n' ',' < file.txt > file2.txt
will work
回答2:
since you have tagged your question with sed, I suggest a sed oneliner, also sed could change your file "in-place" with option "-i"
sed -i ':a $!N; s/\n/,/; ta' file
or with awk
awk '{x=x""sprintf($0",")}END{gsub(/,$/,"",x);print x}' file
no like sed, awk has no "in-place" changing option, you have to :
awk '...' file > /tmp/mytmp && mv /tmp/mytmp file
回答3:
If you just want to replace the newline with , you can us this
awk 'ORS=","' temp.txt > file.txt
来源：https://stackoverflow.com/questions/14675849/tr-command-not-able-to-direct-the-output