Append contents of pattern space to file. This action occurs when the command is encountered rather than when the pattern space is output. Exactly one space must separate the w and the filename. This command will create the file if it does not exist; if the file exists, its contents will be overwritten each time the script is executed. Multiple write commands that direct output to the same file append to the end of the file.
GNU sed allows you to use the special filenames /dev/stdout and /dev/stderr to write to standard output or standard error, respectively.
# Store HTML tables in a file /<table/,/<\/table>/w tables.html