EmbLogic » bash

ls – list command

Ankur Garg — Wed, 10 Feb 2016 17:20:32 +0000

ls – list command
=================
- ls means list directory content
- Prototype :
ls [OPTION] … [FILE] …
- Exit status
It returns 0 ,on success
Returns 1 in case of minor problems (eg. cannot access subdirectory)
returns 2 in case of serious trouble (eg. Cannot access command line argument)
- For specific listing you can use *
eg.1) For listing all files starting with a use :
ls a*
2) for listing all .c files use :
ls *.c
3) for listing all .c files starting with a use :
ls a*.c
- Some common options are :
i) -a –all –> Do not ignore enteries starting with .
Use this to view swap or temporary files.
ii) -l –> long listing format
iii) -r –) Reverse order sort (by name) and list
iv) -s –size –> Print allocated size of each file in blocks
v) -S –> Sort by file size
vi) -t –> Sort by modification time, newest first
vii) -U –> Do not sort; list enteries in directory order
viii) -X –> Sort alphabetically by entry extension.
ix) -F –> to distinguish files from directories (Puts / in directory and * with executable files)
x) -R –> It shows files that are contained in directory. It continued to dirrectory in a directory and so on.

- In fedora for long lsting use command :

CD – Change Directory Command

Ankur Garg — Wed, 10 Feb 2016 17:18:28 +0000

CD – Change Directory Command
=============================
- cd means change working directory
- Prototype:
cd [-L | -P] [directory]
cd -
-If you do not give any directory to cd command, it will take you to home directory.
eg. cd –> It will go to home directory.
- For previous directory use :
cd ..
- Further for more than one previous directory use :
cd ../..
- Directory can be defined by 2 types :
i) Absolute filepath – Path starting from ‘/’.
eg. cd /usr/bin/
ii)Relative Filepath – Path relative to current directory
eg. cd /usr –> Absolute filepath
cd etc –> Relative Filepath

Linux Filesystem

Ankur Garg — Tue, 09 Feb 2016 14:56:41 +0000

Linux Filesystem
================
- In windows, physical drive determines the pathname of the file.
- Windows assigns a letter to each disk drive.
- Each directory contains its own directory structure for accesing files stored in it.
- For eg. in windows filepath is as:
c:\Users\ankur\Documents\Lessons.doc

- Linux does not use drive letters in pathnames like windows.
- Linux stores files within a single directory structure, called a virtual directory.
- Virtual directory contains filepaths from all storage devices installed on PC, mergedinto a single directory.
- There is a single base directory, called the root.
- root drive contains core of virtual directory.
- On root drive, Linux has special directories called mount points.
-When we start a new shell prompt, your session starts in your home directory.

How to get help in Linux – Fedora

Ankur Garg — Tue, 09 Feb 2016 14:54:58 +0000

To get help in fedora
=====================
To learn about any new command, function or utility in Fedora we can get help from it.
It has 3 such commands :-

i) man pages – These are manual pages .
- It contains interface to online reference manuals
- Press q to exit.
- How to Use ( Command ) – man command_name
- for all man pages of BASH shell, use
man bash
- It generally contains following information about command(command_name) :-
* Name
* Synopsis (Prototype)
* Description (Options)
* Author (author of command)
* Reporting Bugs (Feedback emails/Website)
* Copyright (copyright details)
* See Also (for further reference of command)

ii) Info pages – Read info documents
- It contains BASH manuals.
- Press q to exit
- How to Use (command) – info command_name
- It contains information about :-
* Prototype
* Introduction
* Options
* Exit Status
iii) help command
- It gives basic help for using a command and its various options.
- It gives output on Standard Output.
- It do not require exit command.
- How to Use (command) – help command_name
- It contains following information about command (command_name) :-
* Function of command
* Options
* Exit status

eg.
man echo
info echo
help echo

- To check total no. of enteries in each of three
I) type either of three (with space at end)
II) Press tab button for 3-4 times.
We will get the total number of possible options defined or list of them also.
eg. ( means Press tab button)
man

How to change default prompt in BASH shell

Ankur Garg — Sun, 07 Feb 2016 15:46:40 +0000

To change default prompt :-
========================
- We can change default prompt by assigning the character to it.
- Each character have a specific meaning.

BASH Shell Prompt Characters :-
Character Description
\a Bell Character
\d Date in format “Day Month Date”
\e ASCII escape character
\h Local hostname
\H Fully qualified domain hostname
\j Number of jobs currently managed by the shell
\l Basename of the shell’s terminal device name
\n ASCII newline character
\r ASCII carriage return
\s Name of the shell
\t Current time in 24-hour HH:MM:SS format
\T Current time in 12-hour HH:MM:SS format
\@ Current time in 12-hour am/pm format
\u Username of current user
\v Version of BASH shell
\V Release level of bash shell
\w Current working directory
\W Basename of current working directory
\# Command number of this command
\$ A dollar sign if normal user, #(Pound) for root user
/nnn Character corresponding to value nnn
\\ Backslash
\[ Begins a control code sequence
/] Ends a control code sequence

eg.
[ankur@(none) ~]$ PS1 = “[\t][\u]$”
[15:20:30][ankur]$

Command line Prompt – PS1, PS2

Ankur Garg — Sun, 07 Feb 2016 15:44:42 +0000

Command line Prompt
===================
Environmental variables that controls Command line Prompt
PS1 : Controls the format of default command line prompt.
PS2 : Controls the format of second-tier command line prompt.
PS3 : Controls the format of tertiary command line prompt.

- Shell uses default PS1 prompt for initial data entry into shell.
- If we enter a command that requires additional information, shell displays second-tier prompt specified by PS2 .
- To display current settings for prompt use command :
echo $PS1
echo $PS2
- PS3 is used only in shell scripts.