Append output to the beginning of a file.

command > tmp && cat logfile.txt >> tmp && tmp > logfile.txt && rm tmp
Adds the stdout (standard output) to the beginning of logfile.txt. Change "command" to whatever command you like, such as 'ls' or 'date', etc. It does this by adding the output to a temporary file, then adding the previous contents of logfile.txt to the temp file, then copying the new contents back to the logfile.txt and removing the temp file.

What Others Think

Or: cat <(command) logfile.txt >tmp && mv tmp logfile.txt
TheMightyBuzzard · 654 weeks and 4 days ago
You can make that even slicker by using the mktemp command. cat <(command) logfile.txt >$(tmp=$(mktemp blah.XXX) && echo $tmp) && mv $tmp logfile.txt
isaacs · 654 weeks and 4 days ago
I can't think of it now, but there must be some way to to this using 'tac' which is the opposite of cat, meaning it spits out a file's *lines* in reverse order.
bwoodacre · 654 weeks and 4 days ago
Why stop there? How about ( sed -n '1,4p' logfile.txt; some_command; sed -n '4,$p' logfile.txt ) > tmp; mv tmp logfile.txt This *inserts* the output into the middle! For example, if you had a ChangeLog with some header text, but a last-entry-first list. Also, I put the commands in a sub-shell () so I could redirect the output of all of them at once.
flatcap · 654 weeks and 3 days ago
Sorry, typo in the above, my sed ranges overlap. They should have been, '1,4p' and '5,$p' for a 4 line header and 'the rest'.
flatcap · 654 weeks and 3 days ago
Thanks flatcap! I didn't know the sed command until now and wish I had found it when I was trying to figure this out. Very slick. Guess that's why I got a minus 2 rating. This is a harshly judging community.
akoumjian · 654 weeks and 3 days ago
this is my two cents for appending an output on top of an existing file by using sed and awk command | awk '{system("sed "'NR'"i\""$0"\" -i logfile.txt")}'
alperyilmaz · 654 weeks and 2 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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