Insert multiline text before the first matching line in a file

Using awk:

awk 'done != 1 && /DatePattern/ {
    print "log4j.appender.DRFA=org.apache.log4j.RollingFileAppender"
    print "log4j.appender.DRFA.MaxBackupIndex=100"
    print "log4j.appender.DRFA.MaxFileSize=10MB"
    done = 1
    } 1' file >newfile && mv newfile file

This would print the three lines when the first match of DatePattern occurs in the file. The flag done is then set to 1 which stops the lines from being printed again. The trailing 1 at the very end causes every line in the in-data to be printed.

If you want empty lines in the output after the three lines, add \n\n to the end of the last string.

The output is written to newfile and if awk did not encounter any strange errors, the original is then replaced by this once the awk process terminates.

Requested in comments: Adding the lines after the matched line,

awk '1; done != 1 && /DatePattern/ {
    print "log4j.appender.DRFA=org.apache.log4j.RollingFileAppender"
    print "log4j.appender.DRFA.MaxBackupIndex=100"
    print "log4j.appender.DRFA.MaxFileSize=10MB"
    done = 1
    }' file

This moves the 1 (which does the printing of each input line and could be replaced by { print }) to before the code that is triggered when the pattern matches.

Using GNU sed you may approach it this way also:

sed -i -e '
    /DatePattern/!b

    i\
log4j.appender.DRFA=org.apache.log4j.RollingFileAppender\
log4j.appender.DRFA.MaxBackupIndex=100\
log4j.appender.DRFA.MaxFileSize=10MB

    :a;n;$!ba
' input.file

And if you are sure that the DatePattern cannot be on the last line of the file, then you could do this also:

sed -i -e '
    /DatePattern/!b
    r file2add.txt
    N;:a;n;$!ba
' input.file

where you put all the lines to be added into a file, say file2add.txt. Note: with this method, you don't put trailing backslashes in the file file2add.txt.

Since you tagged this query with perl also, so here goes one obvious way:

perl -pi -e '
     print <<\EOF if /DatePattern/ && !$seen++;
log4j.appender.DRFA=org.apache.log4j.RollingFileAppender
log4j.appender.DRFA.MaxBackupIndex=100
log4j.appender.DRFA.MaxFileSize=10MB
EOF
' input.file

Note: The added text mustn't contain the standalone string EOF on a line by itself. The backslashing of the heredoc is necessary , lest any variables get expanded .

If you cannot be sure of the above constraints in the text to add, then do this:

perl -pi -e '
    next if !/DatePattern/ || $seen++;
    open my $fh, "<", "file2add.txt" or die "Could not open file for reading:$!\n";
    $_ = join "", <$fh>, $_;
' input.file

This is a job well-suited to ed, the standard file editor:

/DatePattern/i
log4j.appender.DRFA=org.apache.log4j.RollingFileAppender
log4j.appender.DRFA.MaxBackupIndex=100
log4j.appender.DRFA.MaxFileSize=10MB
.
wq