Bash

Suppose you want to email changes in the Oracle's alert log, or maybe syslog's messages, it would be nice to email new 'tailed' entries. Something like tail -f logfile | mailx ... won't work as tail -f will never pipe any output. The idea is to take a snapshot of the file every x minutes, archive it, take another snapshot after x minutes, diff the two files, and email the changes. Then you roundrobin the snapshot and repeat the whole process:

crontab -l
*/5 * * * * /usr/local/bin/swatch-action.sh > /dev/null 2>&1

[root]# cat /usr/local/bin/swatch-action.sh

To search and replace text in vi:

% (entire file) s (search and replace) /old text with new/ c (confirm) g (global - all)
	:%s/oldstring/newstring/cg 	  	  	

To ignore case during search

:set ic

Let's say you have a list of tables inside a text file called e_tables.txt and you want to generate an SQL file to drop these tables. With sed this is a very easy task to do:

sed -e 's/.*/DROP TABLE & CASCADE CONSTRAINTS;/' e_tables.txt

The code can be interpreted as follows. The ".*" tells sed to match every line and replace it with strings "DROP TABLE", "CASCADE CONSTRAINTS" and the matched line, denoted by "&".

The code is very simple:

while read line; do echo $line; done < file.txt

To output the result to another text file, for example after some text manipulation:

while read line; do echo "Manipulated $line"; done < file.txt > output.txt