How do you append output to a file instead of overwriting it?

Question

Accepted Answer

Use >> instead of > — it adds output to the end of the file, keeping what's already there.
echo "First line"  > file.txt    # > truncates: file now holds just this line
echo "Second line" >> file.txt   # >> appends: file now holds both lines

Operator
Effect on an existing file

>
wipes it first, then writes

>>
leaves it intact, writes at the end

The single vs. double > is the difference between replace and add. It's a one-character mistake with big consequences: > on your logfile silently erases the entire history. Reach for >> whenever a file should accumulate over time — logs, audit trails, or output gathered from many commands in a script.
date              >> log.txt
echo "Backup started" >> log.txt   # each run grows the log instead of resetting it

Tip: 2>> is the stderr equivalent — append errors to an error log without overwriting.

Operator	Effect on an existing file
`>`	wipes it first, then writes
`>>`	leaves it intact, writes at the end