vi Editor - Redo

To perform the redo function using the vi editor use 'Ctrl-R'.

Undo is 'u'.

Login Activity on a Unix Server

To check the login activity on a Unix server you can run the following command:
# last | head

'head' just displays the last 10 logins.

You can also check the login activity of a specific user:
# last user_name | head

Total Memory Installed on Solaris

Use the prtconf command to get the total amount of memory installed on a Solaris machine:
# prtconf

Counting the number of occurrences of each line in a file

To count the number of occurrences of each line in Linux you can use the following command:
sort input_file | uniq -c > output_file

You may want to ignore the case and then apply the count:
cat input_file | tr '[:upper:]' '[:lower:]' | sort | uniq -c > output_file

Removing punctuation from a file in Linux

To remove the punctuation from a file run the following command:
cat input_file | tr -d '[:punct:]' > output_file

Converting all Upper Case letters to Lower Case in Linux

To convert all upper case characters to lower case in Linux, run the following command:
cat input_file | tr '[:upper:]' '[:lower:]' > output_file

Obtaining a specific field from a comma separated file (using awk)

If you have a comma separated file e.g.
Name,DateOfBirth,PlaceOfBirth
Jeff,17-09-1982,London
Maggie,08-06-1976,New York
George,14-02-1991,Johannesburg

and you need to extract only the list date of birth from this file you can use the following awk command:
awk 'BEGIN{FS=","}{print $2}' filename > date_of_birth

where FS indicates the file separator (so if your file is delimited with a different character e.g. ":" you would have FS=":" within the awk command) and "$2" indicates the 2nd column.