Unix FAQ

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Question:

I'm new to Linux and need some basic commands. I am lost how to list a directory, delete or rename a files, and search for strings and files. Apparently I've got a Shell. What is a shell ?

Sorry this is really basic but I don't know where to start..
Thanks,
Maria.

Answer:

Well the short answer to your question is that ls lists a directory, rm deletes and mv renames files. grep searches for strings in files, and find searches for files. A Shell is Unix jargon for a command line interpreter - simply a program you enter commands into and it does something useful with them, well hopefully.

Might by worth mentioning that there are two main flavours of shell - "Bourne" and "C" shells, at some point you may need to find out which you have, but at the moment its not that important to you.

Below are some basic Unix commands you'll find useful, these are intended for both beginners & intermediate users, in alphabetical order;

What no feedback ?

One quirk of many Unix commands that newcomers find disturbing it they don't report anything if the command succeeds. This is probably most perturbing with command like rm and rmdir which delete files and directories;

shell% touch somefile
shell% ls -l somefile
-rw-------   1 andrew   mercury        0 Jun 11 16:35 somefile
shell% rm somefile
shell%

shell% rm somefile
somefile: No such file or directory
shell% 

The behaviour seems a little odd if you're used to verbose operating systems like Windows or VMS, but this is all part of the Unix philosophy - why report anything when's there's nothing to say?
You could liken it to the difference between men and women    [ You could, I couldn't. I'm married......]

Getting Help; The manual and the 'man' command.

There's no help command for Unix, well if there is your site has made some special effort to provide it. The nearest thing is the man command - manual page. Say we wanted more information about the 'mkdir' command.

shell% man mkdir
User Commands                                            mkdir(1)

NAME
     mkdir - make directories

SYNOPSIS
     mkdir  [ -m mode ]  [ -p ] dir ...

DESCRIPTION
     The mkdir  command creates the named directories in mode 777
     (possibly altered by the file mode creation mask umask(1)).

     Standard entries in a directory  (for  instance,  the  files
     ".", for the directory itself, and "..", for its parent) are
     made automatically. mkdir  cannot create  these  entries  by
     name.  Creation  of a directory requires write permission in
     the parent directory..........

The synopsis shows how to use the command and any options it may have. The square brackets '[]' indicate that that parameter is optional. In this case mkdir has the options -m and -p. -m requires a mode argument. The parameter dir (name of directory) is compulsory. The '...' denotes that there can be more 'dir' arguments - you can create multiple directories with one command.

Manual page sections

Note the top line of the above manual page - mkdir(1).

You'll likely witness this a lot as you learn more about Unix. The number in brackets is the section number in the manual. The entry above came from section 1 - User Commands.

You may come across references like "see lpc(8) for more information". This simply is referring you to the entry for lpc (line printer control) in section 8 of the manual.

You can specify the section number to the man command, on Solaris use 'man -s 2 mkdir', on Linux and some other systems you should use 'man 2 mkdir'.

shell% man -s 2 mkdir 
System Calls                                             mkdir(2)


NAME
     mkdir - make a directory


SYNOPSIS
     #include <sys/types.h>
     #include <sys/stat.h>

     int mkdir(const char *path, mode_t mode);

DESCRIPTION 
   .............

Now you can see there is another manual page entry for mkdir, this time in section #2 - System Calls. This section is primarily aimed at programmers, we shown it here simply to demonstrate that the same name can exist in different sections. If you use the man command and see something completely unexpected check the man page section at top of the page.

Keyword searches / Finding a command

Before finishing up with the 'man' command one last useful feature is worth a mention - keyword searches. By using the '-k' option on the 'man' command you can find all the commands with that word in their description field. This can be quite useful when you don't know the name of a command;

shell% man -k mkdir

sun (bash) % man -k mkdir
mkdir           mkdir (1)       - make directories
mkdir           mkdir (2)       - make a directory
mkdirp          mkdirp (3g)     - create, remove directories in a path
nis_mkdir       nis_server (3n) - miscellaneous NIS+ functions
nismkdir        nismkdir (1)    - create NIS+ directories
rmdirp          mkdirp (3g)     - create, remove directories in a path     

Tips:

To search for a string (e.g "xyx") in all the files in the current directory, try;
    % find . -type f -exec grep xyz '{}' /dev/null \;
This causes find to run "grep xyz <file>" on every plain file ("-type f")