Command Line Kung-Fu

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Command Line Kung-Fu
Bash / vi / Perl
By: Ed Williams - CTL

Biff-Bash-Bosh
 /bin/bash available on most flavours of *nix.
- You all know about the arrow keys and tab completion!?
- We’ll dig a little deeper!

Bash - History
 Use the ‘history’ command to display your history:
 Tip: alias the ‘history’ command to ‘h’ in your .bashrc

Bash – History by Numbers
 Select a particular command using !<n>
 You can also use this notation in the middle of a command – e.g.

Bash – History by Numbers
 Even two [or more] commands can be combined together.

Searching history – my fav!!
 Search backwards using ctrl-r
 Hit ctrl-r, start typing the string you are looking for, the shell will
show the most recent match – ctrl-r again will take you further
back.
 Once you have the command:
 Enter will execute chosen command
 Escape / ctrl-j will place the command on the command line for editing
 ctrl-g / ctrl-c to cancel

Bash - Keyboard Accelerators
 ‘!!’ Repeats the previous command
 Similarly, ‘!-2’ [and -3...] repeats the command before the
previous command

Bash – Specifying Arguments
 ‘!$’ gets the last argument from the previous command:

Bash – Specifying Arguments
• ‘!*’ gets all of the previous arguments
• You could use substitution with ‘^’ (only replaces first instance - no
global replacement)

Bash – Fast Searching
• !<string> executes the last command that begins with
<search>
• This can be risky – so ensure you use the :p option
to print the last command

Good ol’ vi
Good ol’ vi

Good ol’ vi
 Ubiquitous. Essentially all Unix and Unix-like systems come with vi.
 AIX, Solaris, and all Linux variants
 Its very flexible and, once you get the hang of it, very quick for
development.

vi – Command Line Options
 Vi command Line Options
- vi –R file_name
- Opens file in read-only mode (or view file_name)
- vi + file_name
- Goes to the last line of file_name
- vi +n file_name
- Goes to the n’th line of file_name
- e.g. Will take you to all the Max / Min lengths variables in the
john.conf file

vi – Command Line Options
 vi +/pattern file_name
Start editing at the first line matching pattern

And for the hard core......
 Vi on the command line:
 Vi commands such as x, dd, 0, D etc. will now work

....and for the not so hardcore
 To knock the option off 

Vi and ex – address symbols
- 1G – goes to first line
- G – goes to last line
- 1,$ - all lines in file
- % - entire file
- . - current line
- $ - last line

Vi/ex tips and tricks
 Ex commands -
- :%d - delete all lines (same as :1,$d)
- :g/1/d - delete all occurrences of 1
- :%s/^M//g - removes carriage return – useful!
- Actually replaces ^M with null space
- :g/.*/m0 - reverse the order of the lines
- :g/^$/d - removes all blank lines
 Note – to get the ^M, <ctrl>v and enter.
- *m0 is the ex command to move the line to line 0.

Vi/ex tips and tricks
 Use % to match brackets – useful when dealing with regular expressions.
 The $HOME/.exrc file can be used to hold certain config options e.g. The
following are set in my .exrc file (viewed with the set command)
 set ic sm showmode
 “set nu

Vi Mappings
 Key Mapping – this is used to change the meaning of typed keys –
these mappings are held in $HOME/.exrc

Command Line Perl
Command Line Perl

Command Line Perl
 Why bother?
 Perl is pretty much standard on all *nix installs.
 Perl does a lot of the common stuff for you.
 Better than grep:
• - better sub-string matching
 String Escapes for control characters
 Line-spanning matches

Command Line Perl
 Better than awk (?): - No way to specify ranges
- No way to disable input parsing

Command Line Perl
 With the use of –M, you can use perl modules*:
 Tip: use –c as a sanity check before executing commands:

Golf & Command line perl
 Create a prog / script that will list all uid 0 users:
#! /usr/bin/perl –w
foreach (`cat /etc/passwd`) {
@line = split(/:/);
print if $line[2] =~ /^0$/
}
Note: perl increments from 0, hence $line[2] for the third element,
unlike awk**

Command line perl – cont’d....
 And from the command line:
 There is a lot going on here - lets break it down into its separate
components:
 -e - The option lets you specify a single line of code on the
command line

-n - This option places a loop around the command, in the form of:
While (<>) {
..command..
}
Note: -p adds a ‘print $_;’
-a - this will feed input lines to the split() function. The results of
the split are placed into the @F variable

 Now that we are splitting, we need to know what to split on:
 -F - lets you change the regular expression that is used to split the
input lines e.g.
–F/:/
 -l - This option turns on line-ending processing – in effect,
chomp()’s and adds ‘n’ – really useful for one-liners!

Removing ^M with command line perl
 File with ^M’s
 Run the command
 more of new_car

Resources

Any Questions?
*see http://www.cpan.org/
**awk -F: ‘{if ($3==0) print $F}’ /etc/passwd

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