unix commands part-1

simple and frequent use commands -- can not update all same time will update more day by day

cd ==> change directory.
ls ==> the list command.
mkdir ==> allows the user to make a new directory
rmdir ==> remove directory(Be very careful using the rm command).
rm ==> the rmdir command will remove directories and files held within, the rm command. will delete created files(Be very careful using the rm command).
CP ==> allows a user to copy a file to another folder or directory.
mv ==> allows a user to move a file to another folder or directory.
touch ==> allows users to make files using the(exaple touch test.txt).

more ==> Look at file, one page at a time.
cat ==> concatenate and display files.
bdf ==> See how much free disk space (in linux use df ).
du ==> Estimate disk usage of directory in Bytes.
top ==> Print system usage and top resource .
gzip ==> compress file (ex: gzip filename).
gunzip ==> Uncompress file (ex: gunzip compressedfile.gz).
passwd ==> Change passwd.
chmod ==> Change permissions(it need more explanation it will explain in part-2)
chown ==> Change ownership(it need more explanation it will explain in other post)

who ==> Lists who is logged on your machine.
history ==> Lists commands you've done recently.
date ==> Print out current date.

======================to get more detail or help for above commds==========

man ==> this command is helps you give detail view of other command

example :- i will take ls command ls ==> is use for list

$ man ls ==> output will be like below

$ man ls

ls(1) ls(1)

NAME

ls, lc, l, ll, lsf, lsr, lsx - list contents of directories

SYNOPSIS

ls [-abcdefgilmnopqrstuxACFHLR1] [names]

lc [-abcdefgilmnopqrstuxACFHLR1] [names]

l [ls_options] [names]

ll [ls_options] [names]

lsf [ls_options] [names]

lsr [ls_options] [names]

lsx [ls_options] [names]

DESCRIPTION

For each directory argument, the ls command lists the contents of the

directory. For each file argument, ls repeats its name and any other

information requested. The output is sorted in ascending collation

order by default (see Environment Variables below). When no argument

is given, the current directory is listed. When several arguments are

given, the arguments are first sorted appropriately, but file

arguments appear before directories and their contents.

If you are a user with appropriate privileges, all files except . and

.. are listed by default.

There are three major listing formats. The format chosen depends on

whether the output is going to a login device (determined by whether

output device file is a tty device), and can also be controlled by

option flags.

The default format for a login device is to list the contents of

directories in multicolumn format, with entries sorted vertically by

column. (When individual file names (as opposed to directory names)

appear in the argument list, those file names are always sorted across

the page rather than down the page in columns because individual file

names can be arbitrarily long.) If the standard output is not a login

device, the default format is to list one entry per line.

The -C and -x options enable multicolumn formats, and the -m option

enables stream output format in which files are listed across the

page, separated by commas. In order to determine output formats for

the -C, -x, and -m options, ls uses an environment variable, COLUMNS,

to determine the number of character positions available on each

output line. If this variable is not set, the terminfo database is

used to determine the number of columns, based on the environment

variable TERM. If this information cannot be obtained, 80 columns is

assumed.

The command lc functions the same as ls except that the lc default

output is columnar, even if output is redirected.

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Options

ls recognizes the following options:

-a List all entries; usually entries whose names begin with a

period (.) are not listed.

-b List nonprinting characters in the octal \ddd notation.

-c Use time of last modification of the inode (file created,

mode changed, etc.) for sorting (-t) or printing (-l (ell)).

-d If an argument is a directory, list only its name (not its

contents); often used with -l (ell) to get the status of a

directory.

Under the UNIX 2003 environment (see standards(5)), ls with

-d does not follow symbolic links unless the -H or -L option

is specified.

-e List the extent attributes of the file. If any of the files

has a extent attribute, this option lists the extent size,

space reserved and allocation flags. This option must be

used with the -l (ell) option.

-f Interpret each argument as a directory and list the name

found in each slot. This option disables -l (ell), -r, -s,

and -t, and enables -a; the order is the order in which

entries appear in the directory.

-g Same as -l (ell), except that only the group is printed

(owner is omitted). If both -l (ell) and -g are specified,

the owner is not printed.

-i For each file, list the inode number in the first column of

the report. When used in multicolumn output, the number

precedes the file name in each column.

-l (ell) List in long format, giving mode, number of links,

owner, group, size in bytes, and time of last modification

for each file (see further DESCRIPTION and Access Control

Lists below). If the time of last modification is greater

than six months ago, or any time in the future, the year is

substituted for the hour and minute of the modification

time. If the file is a special file, the size field

contains the major and minor device numbers rather than a

size. If the file is a symbolic link, the filename is

printed, followed by -> and the pathname of the referenced

file.

Under the UNIX 2003 environment (see standards(5)), ls with

-l does not follow symbolic links unless the -H or -L option

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is specified.

-m Stream output format.

-n The same as -l, (ell) except that the owner's UID and

group's GID numbers are printed, rather than the associated

character strings.

-o The same as -l, (ell) except that only the owner is printed

(group is omitted). (If both -l (ell) and -o are specified,

the group is not printed).

-p Put a slash (/) after each file name if that file is a

directory.

-q List nonprinting characters in file names as the character

(?).

-r Reverse the order of sort to get reverse (descending)

collation or oldest first, as appropriate.

-s List size in blocks of 512-byte units, including indirect

blocks, for each entry. The first entry listed is the total

number of blocks in the directory. When used in multicolumn

output, the number of blocks precedes the file name in each

column. The number of indirect blocks in a file is

filesystem dependent.

-t Sort by time modified (latest first) before sorting

alphabetically.

-u Use time of last access instead of last modification for

sorting (-t option) or printing (-l (ell) option).

-x List multicolumn output with entries sorted across rather

than down the page.

-A The same as -a, except that the current directory . and

parent directory .. are not listed. For a user with

appropriate privileges, this flag defaults to on, and is

turned off by -A.

-C List multicolumn output with entries sorted down the

columns.

-F After each file name, put one of:

+ A slash (/) if the file is a directory or a symbolic link

to a directory.

+ An asterisk (*) if the file is executable;

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+ An at-sign (@) if the file is a symbolic link to a file;

+ A vertical bar (|) if the file is a fifo.

Under the UNIX 2003 environment (see standards(5)), ls with

-F does not follow symbolic links unless the -H or -L option

is specified.

-H If a symbolic link referencing a file of type directory is

specified on the command line, ls evaluates the file

information and file type to be those of the file referenced

by the link, and not the link itself. However, ls writes the

name of the link itself and not the file referenced by the

link.

-L Evaluate the file information and file type for all symbolic

links (whether named on the command line or encountered in a

file hierarchy) to be those of the file referenced by the

link, and not the link itself. However, ls writes the name

of the link itself and not the file referenced by the link.

When -L is used with -l, write the contents of symbolic

links in the long format.

-R Recursively list subdirectories encountered.

-1 (one) List the file names in single column format regardless

of the output device. This forces single column format to

the user's terminal.

Specifying more than one of the options in the following mutually

exclusive pairs is not considered an error: -C and -l (ell), -m and -l

(ell), -x and -l (ell), -C and -1 (one), -H and -L, and -c and -u.

ls is known by several shorthand-version names for the various

formats:

l is equivalent to ls -m

ll is equivalent to ls -l (ell)

lsf is equivalent to ls -F

lsr is equivalent to ls -R

lsx is equivalent to ls -x

The shorthand notations are implemented as links to ls. Option

arguments to the shorthand versions behave exactly as if the long form

above had been used with the additional arguments.

Mode Bits Interpretation (-l option)

The mode printed in listings produced by the -l (ell) option consists

of 10 characters, for example, -rwxr-xr-x.

The first character indicates the entry type:

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b Block special file

c Character special file

d Directory

l Symbolic link

n Network special file

p Fifo (also called a "named pipe") special file

s Socket

- Ordinary file

The next 9 characters are interpreted as three sets of three

characters each which identify access and execution permissions for

the owner, group, and others categories, as described in chmod(1).

The - indicates the permission is not granted. The various

permissions can be put together in any combination, except that the x,

s, S, t, and T characters are mutually exclusive, as implied below.

-r-------- Read by owner

--w------- Write by owner

---x------ Execute (or search directory) by owner; do not set

user ID on execution

---s------ Execute/search by owner; set user ID on execution

---S------ No execute/search by owner; set user ID on

execution

----r----- Read by group

-----w---- Write by group

------x--- Execute/search by group; do not set group ID on

execution

------s--- Execute/search by group; set group ID on execution

------S--- No execute/search by group; set group ID on

execution

-------r-- Read by others

--------w- Write by others

---------x Execute/search by others; do not set sticky bit on

execution

---------t Execute/search by others; set sticky bit on

execution

---------T No execute/search by others; set sticky bit on

execution

The mode characters are interpreted as follows:

- Deny all permissions in the corresponding position.

r Grant read permission to the corresponding user class.

w Grant write permission to the corresponding user class.

x Grant execute (or search in directory) permission to the

corresponding user class.

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s Grant execute (search) permission to the corresponding user

class. Execute the file as if by the owner (set user ID,

SUID) or group (set group ID, SGID), as indicated by

position.

S Deny execute (search) permission to the corresponding user

class. Execute the file as if by the owner (set user ID,

SUID) or group (set group ID, SGID), as indicated by

position.

t Grant execute (search) permission to others. The "sticky"

bit is set (see the description of S_ISVTX in chmod(2)).

T Deny execute (search directory) permission to others. The

"sticky" bit is set.

When an option is specified that results in a listing of directory

and/or file sizes in bytes or blocks (such as the -s or -l (ell)

option), a total count of blocks, including indirect blocks, is also

printed at the beginning of the listing.

Access Control Lists (ACLs)

If a file has optional ACL entries, the -l (ell) option displays a

plus sign (+) after the file's permissions. The permissions shown are

a summary representation of the file's access control list, as

returned by stat() in the st_mode field (see stat(2)). To list the

contents of an access control list, use the lsacl command (see

lsacl(1) and acl(5)) for HFS file systems, or the getacl command (see

getacl(1) and aclv(5)) for JFS file systems.

EXTERNAL INFLUENCES

For information about the UNIX standard environment, see standards(5).

Environment Variables

If the COLUMNS variable is set, ls uses the width provided in

determining positioning of columnar output.

LANG determines the locale to use for the locale categories when both

LC_ALL and the corresponding environment variable (beginning with LC_)

do not specify a locale. If LANG is not set or is null, it defaults

to C (see lang(5)).

LC_COLLATE determines the order in which the output is sorted.

LC_CTYPE determines which characters are classified as nonprinting for

the -b and -q options, and the interpretation of single- and/or

multibyte characters within file names.

LC_TIME determines the date and time strings output by the -g, -l

(ell), -n, and -o options.

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LC_MESSAGES determines the language in which messages (other than the

date and time strings) are displayed.

If any internationalization variable contains an invalid setting, they

all default to C (see environ(5)).

International Code Set Support

Single- and multibyte character code sets are supported.

RETURN VALUE

ls exits with one of the following values:

0 All input files were listed successfully.

>0 ls was aborted because errors occurred when accessing files.

The following conditions cause an error:

+ Specified file not found.

+ User has no permission to read the directory.

+ Process could not get enough memory.

+ Invalid option specified.

EXAMPLES

Print a long listing of all the files in the current working directory

(including the file sizes). List the most recently modified

(youngest) file first, followed by the next older file, and so forth,

to the oldest. Files whose names begin with a . are also printed.

ls -alst

WARNINGS

Setting options based on whether the output is a login (tty) device is

undesirable because ls -s is very different from ls -s | lp. On the

other hand, not using this setting makes old shell scripts that used

ls almost inevitably fail.

Nonprinting characters in file names (without the -b or -q option) may

cause columnar output to be misaligned.

DEPENDENCIES

NFS

The -l (ell) option does not display a plus sign (+) after the access

permission bits of networked files to represent existence of optional

access control list entries.

AUTHOR

ls was developed by AT&T, the University of California, Berkeley and

HP.

FILES

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/etc/group For group IDs for -l (ell) and -g.

/etc/passwd For user IDs for -l (ell) and -o.

/usr/share/lib/terminfo/?/* For terminal information.

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Anuroop Challa