Here are some useful command line tips and tricks for Linux/Unix systems. Indispensable are commands to find certain processes or files which match a specific name or keyword:

$ ps ax | grep "tomcat"    # returns all instances of tomcat runnning on your system
$ find . -name *xml        # find all XML files in the current directory
$ grep -r keyword *        # find all Files which match a certain keyword recursively

If you want to inspect log files, the following commands are useful. The grep command is useful to get all log file entries for a certain expression with a short description (-Ax means list x lines after the match) e.g. to list all logins, all registrations, or all exceptions of a certain kind

$ tail -f error.log        # view live access to log file
$ grep -A1 keyword *.log   # find all lines around the match for a certain keyword, 
                           # i.e. all logins for the keyword="SessionsController#create"

Various commands are available to add and count line numbers..

$ ls | nl                  # Numerates files in a directory 
$ ls | wc -l               # Count the number of files in a directory 
$ cat README | wc -l       # Count the number of lines in a file
$ nl -ba README            # Show file content with line numbers

Some essential file system operations:

$ ls -lsrt                            # file list sorted by (reverse) timestamp.
$ scp file.txt username@server:~      # copy file from local machine to remote server
$ scp username@server:~/file.txt .    # copy file from remote server to local machine