Sed - Deleting lines matching a pattern

sed -i '/.*log$/d' file_names.txt

Deletes all the lines ending with "log" from the file "file_names.txt"

sed : inplace replacement

It is easy to open a file in vim and do a search replace - but if the file runs into huge sizes, a regular editor would not be able to perform search and replace tasks on it efficiently. For these situation, you need a "stream" editor. Here is an example for replacing "foo" with "bar" in a file called snafu.txt

sed -i -e 's/foo/bar/g' snafu.txt


Where:

-i : Is for inplace replacement

-e: sed script to be run on the file

Regular Expressions Across Multiple Lines

I was looking at this huge java file which had hundreds of SQL statements and thousands of java code interleaved like a spaghetti ! What I really needed was to analyze all the SQL statements in the file since they were all related to a single application which we were supposed to modify. I needed a mechanism to extract all the SQL statements from the file for sake of brevity.

Simple regular expressions using vim or sed did not work since they all deal with a single line, but each one of them provide a mechanism to match regular expression over multiple lines.

sed - the following command will extract all lines between a 'select' and the first ';' following that. Hence you would have printed all the sql queries from a file

sed -ne '/^select/,/;/p' SqlIntensiveFile.java

vim - using the 'g' command can achieve the same. For e.g. the following will delete all the sql queries from the file.

%g/select/,/;/d