ESSENTIAL COMMANDS IN SHELL SCRIPT
ESSENTIAL COMMANDS IN SHELL SCRIPT
LS
COMMAND:-
ls command is one of
the most frequently used command in Linux. I believe ls command is
the first command you may use when you get into the command prompt of Linux
Box.
1. List Files using ls with no option
ls with no
option list files and directories in bare format where we won’t be able to view
details like file types, size, modified date and time, permission and links
etc.
# ls
0001.pcap Desktop Downloads index.html install.log.syslog Pictures
Templates
anaconda-ks.cfg Documents
fbcmd_update.php install.log Music
Public Videos
2 List Files With option –l
Here, ls
-l (-l is character not one) shows file or directory, size, modified
date and time, file or folder name and owner of file and its permission.
# ls -l
total
176
-rw-r--r--.
1 root root 683 Aug 19 09:59 0001.pcap
-rw-------.
1 root root 1586 Jul 31 02:17 anaconda-ks.cfg
drwxr-xr-x.
2 root root 4096 Jul 31 02:48 Desktop
drwxr-xr-x.
2 root root 4096 Jul 31 02:48 Documents
drwxr-xr-x.
4 root root 4096 Aug 16 02:55 Downloads
-rw-r--r--.
1 root root 21262 Aug 12 12:42 fbcmd_update.php
3. Sort Files by File Size
With combination
of -lS displays file size in order, will display big in size first.
# ls -lS
total
176
-rw-r--r--.
1 root root 48867 Jul 31 02:17 install.log
drwxr-xr-x.
2 root root 4096 Jul 31 02:48 Desktop
4. Display Inode number of File or
Directory
We can see some
number printed before file / directory name. With -ioptions list
file / directory with inode number.
# ls -i
20112
0001.pcap 23610 Documents 23793 index.html 23611 Music 23597 Templates
23564
anaconda-ks.cfg 23595 Downloads 22 install.log 23612 Pictures 23613 Videos
23594
Desktop 23585
fbcmd_update.php 35
install.log.syslog 23601 Public
CD COMMAND:-
The cd command, also known as chdir (change directory), is a command-line OS shell command
used to change the current working directory in operating systems such
as Unix, DOS, OS/2, AmigaOS (where if a
bare path is
given, cd is implied), Windows, and Linux. It is also
available for use in shell scripts and batch files. The system call that
affects the command in most operating systems is chdir that is defined
by POSIX
EXAMPLE OF CD COMMAND:-
user@wikipedia:~$
ls
workreports
games encyclopedia text.txt
user@wikipedia:~$ cd games
user@wikipedia:~/games$
cd by itself or cd ~ will always put you in your home directory.
cd . will leave you in the same
directory you are currently in (i.e. your current directory won't change). This
can be useful if your shell's internal code can't deal with the directory you
are in being recreated; running cd . will place your shell in the recreated
directory.
cd ~username will put you in
username's home directory.
cd dir (without a /) will put you
in a subdirectory; for example, if you are in /usr, typing cd bin will
put you in /usr/bin, while cd /bin puts you in /bin.
cd .. will move you up one
directory. So, if you are /usr/bin/tmp, cd .. moves you to /usr/bin,
while cd ../.. moves you to /usr (i.e. up two levels). You can use
this indirection to access subdirectories too. So, from /usr/bin/tmp, you can
use cd ../../local to go to /usr/local.
cd - will switch you to the
previous directory. For example, if you are in /usr/bin/tmp, and go to /etc.,
you can type cd - to go back to /usr/bin/tmp. You can use this to
toggle back and forth between two directories
MV COMMAND:-
mv command.
mv command
is used to move files and directories.
mv
command syntax
$
mv [options] source dest
mv
command options:
|
option
|
description
|
|
mv -f
|
force move by
overwriting destination file without prompt
|
|
mv -i
|
interactive
prompt before overwrite
|
|
mv -u
|
update - move
when source is newer than destination
|
|
mv -v
|
verbose -
print source and destination files
|
|
man mv
|
help manual
|
EXAMPLE
OF MV COMMAND:-
Move main.c
def.h files to /home/usr/rapid/ directory:
$
mv main.c def.h /home/usr/rapid/
MAN
COMMAND:-
On Linux and other Unix-like operating systems, man is the interface used to view
the system's reference manuals.
MAN COMMAND SYNTAX:-
man [-C file] [-d] [-D] [--warnings[=warnings]] [-R encoding]
[-L locale]
[-m system[,...]] [-M path] [-S list] [-e extension]
[-i|-I]
[--regex|--wildcard] [--names-only] [-a] [-u] [--no-subpages] [-P pager]
[-r prompt] [-7] [-E encoding] [--no-hyphenation] [--no-justification]
[-p string] [-t] [-T[device]] [-H[browser]] [-X[dpi]]
[-Z]
[[section] page ...] ...
|
-h, --help
|
Print a help
message and exit.
|
|
-V, --version
|
Display
version information and exit.
|
|
-C file, --config-file=file
|
Use
configuration file file rather
than the default of ~/.manpath.
|
|
-d, --debug
|
Print debugging information.
|
|
-D, --default
|
This option,
when used, is normally specified as the first option; it resets man's behaviour to its default. Its
use is to reset those options that may have been set in $MANOPT. Any options that
follow -D will have
their usual effect.
|
|
--warnings[=warnings]
|
Enable
warnings from the groff text
formatter. This may be used to perform sanity checks on the source text of
manual pages. The warnings is
a comma-separated list of warning names; if it is not supplied, the default
is "mac". See the
"Warnings"node in
the groff info page for a list
of available warning names.
|
MKDIR COMMAND:-
The mkdir command in UNIX
allows users to create directories or folders as they are referred to in some
operating systems. The mkdir command can create multiple directories
at once and also set permissions when creating the directory. The user running
the command must have appropriate permissions on the parent directory to create
a directory or will receive a permission denied error.
How to create a
directory
To create a
directory in UNIX or Linux using the mkdir command pass the name of
directory to the mkdir command.
mkdir
mydirectory
ls
mydirectory
syntax of mkdir
mkdir directory
The rmdir command removes empty directories from
your filesystem.
Description
The rmdir command removes each
directory specified on the command line, if they are empty. That is, each
directory removed must contain no files or directories, or it cannot be removed
by rmdir.
Syntax
rmdir
[-p] [-v | --verbose] [--ignore-fail-on-non-empty] directory ...
|
-p
|
|
|
-v,
--verbose |
Display verbose information
for every directory processed.
|
|
--ignore-fail-on-non-empty
|
Do not report
a failure which occurs solely because a directory is non-empty. Normally,
when rmdir is instructed
to remove a non-empty directory, it reports an error. This option suppresses
those error messages.
|
|
--help
|
Display a help
message, and exit.
|
|
--version
|
Output version
information, and exit.
|
Examples
rmdir mydir
Remove the
directory mydir, if it is
empty.
rmdir dir1 dir2 dir3
The rm ("remove") command
is used to delete files. When used
recursively, it may be used to delete directories.
Description
rm removes
each file specified on the command line. By default, it does not remove
directories; see removing
directories below for details
Syntax
rm
[-f | --force] {[-i | --interactive[=always]] | [-I | --interactive=once] |
[--interactive=never]} [--one-file-system] [--no-preserve-root |
--preserve-root] [-r | -R | --recursive] [-d | --dir] [-v | --verbose]
FILE...
|
-f,
--force |
Ignore
nonexistant files, and never prompt before
removing.
|
|
-i
|
Prompt before
every removal.
|
|
-I
|
Prompt once
before removing more than three files, or when removing recursively. This
option is less intrusive than -i,
but still gives protection against most mistakes.
|
|
--interactive[=WHEN]
|
Prompt
according to WHEN: never, once (-I),
or always (-i). If WHEN is not specified, then prompt always.
|
|
--one-file-system
|
When removing
a hierarchy recursively,
skip any directory that is on a file system different from that of the
corresponding command line argument
|
|
--no-preserve-root
|
Do not treat
"/"(the root directory)
in any special way.
|
|
--preserve-root
|
Do not remove
"/"(the root
directory), which is the default behavior.
|
|
-r,
-R, --recursive |
Remove
directories and their contents recursively.
|
|
-d,
--dir |
Remove empty
directories. This option permits you to remove a directory without
specifying -r/-R/--recursive, provided that the directory is empty. In other
words, rm -d is
equivalent to using rmdir.
|
|
-v,
--verbose |
Verbose mode;
explain at all times what is being done.
|
|
--help
|
Display a help
message, and exit.
|
|
--version
|
Display
version information, and exit.
|
NAME
clear -
clear the terminal screen
SYNOPSIS
clear
DESCRIPTION
clear clears your screen if this is
possible. It looks in the environment for the terminal type and then in the terminfo
database to figure out how to clear the screen. clear ignores any command-line
parameters that may be present.
OPTIONS
|
--help
|
display help
and exit
|
EXAMPLES
Clear the terminal
$ clear
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