Variable Meaning $_ The default or implicit variable. @_ Within a subroutine the array @_ contains the parameters passed to that subroutine. $a, $b Special package variables when using sort() $<digit> Contains the subpattern from the corresponding set of capturing parentheses from the last pattern match, not counting patterns matched in nested blocks that have been exited already. $. Current line number for the last filehandle accessed. $/ The input record separator, newline by default. $| If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel. Default is 0 (regardless of whether the channel is really buffered by the system or not; $| tells you only whether you've asked Perl explicitly to flush after...

These variables are set or used by the Unix shell to modify its behavior. Variable Description ENV=file Name of script that gets executed at startup; Usually, ENV=$HOME/.kshrc FCEDIT=file Editor used by fc (fix command) command. If $FCEDIT is not defined, use $EDITOR, otherwise use the default (vi or ed). FPATH=dirs Directories to search for function definitions; undefined functions are set via typeset -fu . FPATH is searched when these functions are first referenced. HISTFILE=file File in which to store command history. Default is $HOME/.sh_history for Korn shell, $HOME/.bash_history for Bash. If not set, history is lost after logout. HISTSIZE=n Max number of commands to keep in history. HOME=dir Home directory; set by login from passwd file. IFS='chars' Internal field separators. Default is space, tab, and...

The command lsof lists all open files. Here are some simple uses: 1. List what files are in use by process with id 2512: /usr/sbin/lsof -p 2512 2. To find the process that has /u/abe/foo open, use: lsof /u/abe/foo 3. To find who's accessing the CDROM: $ /usr/sbin/lsof /media/cdrom COMMAND PID ... 4. To list all files using any protocol on port 80: lsof -i :80 This is a link to the man page: http://www.netadmintools.com/html/lsof.man.html

In vi mode ( set -o vi ), hit ESC-\ (escape-backslash) for file name completion. In emacs mode, hit ESC-ESC . For file list hit the ESC key followed by the = key.

Use the nm command to list symbols in object files: nm file1.o # default is a.out, if no file na... here's a typical output: 08049568 A __bss_start 080482fc t call_gmon...

Show current directory (print working directory) pwd Show contents of a directory ls (list current directory) ls <directory name> ls -l (list directory, long form) Change to parent directory cd .. Change to previous directory cd - Create a new directory mkdir Remove a directory rmdir Rename a directory or file mv <old_name> <new_name>