UNIX Command Summary

List of All Unix/Linux Command.

Used to check the accessibility of files

Access(pathname, access_mode)
Char* pathname;
int access-mode;
The access modes are.
04 read
02 write
01 execute (search)
00 checks existence of a file

prints the specified string in large letters. Each argument may be upto 10 characters long.


is used to break out of a loop. It does not exit from the program.

Produces a calender of the current month as standard output. The month (1-12) and year (1-9999) must be specified in full numeric format.

Cal [[ month] year]

Displays contents of the calendar file

case operator
The case operator is used to validate multiple conditions.

Case $string in

Pattern 1)
Command list;;
Command list;;

Pattern 3)
Command list;;

(for concatenate) command is used to display the contents of a file. Used without arguments it takes input from standard input <Dtrl d> is used to terminate input.

cat [filename(s)]
cat > [filename]
Data can be appended to a file using >>

Some of the available options are :
Cat [-options] filename(S)
-s silent about files that
cannot be accessed
-v enables display of non printinging characters (except tabs, new lines, form-

-t when used with –v, it causes tabs to be printed as ^I’s
-e when used with –v, it causes $ to be printed at the end of each line
The –t and –e options are ignored if the –v options is not specified.

Used to change directories

Changes the group that owns a file.
Chgrp [grou –id] [filename]

Allows file permissions to be changed for each user. File permissions can be changed only by the owner (s).
Chmod [+/-][rwx] [ugo] [filename]

Used to change the owner of a file.
The command takes a file(s) as source files and the login id of another user as the target.
Chown [user-id] [filename]

The cmp command compares two files (text or binary) byte-by-byte and displays the first occurrence where the files differ.
Cmp [filename1] [filename2] -1 gives a long listing

The comm command compares two sorted files and displays the instances that are common. The display is separated into 3 columns.
Comm. filename1 filename2
first displays what occurs in first files but not in the second
second displays what occurs in second file but not in first
third displays what is common in both files

continue statement
The rest of the commands in the loop are ignored. It moves out of the loop and moves on the next cycle.

The cp (copy) command is used to copy a file.
Cp [filename1] [filename2]

cpio(copy input/output)
Utility program used to take backups.
Cpio operates in three modes:
-o output
-i input
-p pass

the system call creates a new file or prepares to rewrite an existing file. The file pointer is set to the beginning of file.
int creat(path, mode)

char *path;
int mode;

used to cut out parts of a file. It takes filenames as command line arguments or input from standard input. The command can cut columns as well as fields in a file. It however does not delete the selected parts of the file.
Cut [-ef] [column/fie,d] filename
Cut-d “:” –f1,2,3 filename
Where –d indicates a delimiter specified within “:”

used to find the number of free blocks available for all the mounted file systems.
#/etc/df [filesystem]

the diff command compares text files. It gives an index of all the lines that differ in the two files along with the line numbers. It also displays what needs to be changed.
Diff filename1 filename2

The echo command echoes arguments on the command line.
echo [arguments]

Displays the permanent environment variables associated with a user’s login id

exit command
Used to stop the execution of a shell script.

expr command
Expr (command) command is used for numeric computation.
The operators + (add), -(subtract), *(multiplu), /(divide), (remainder) are allowed. Calculation are performed in order of normal numeric precedence.

The find command searches through directories for files that match the specified criteria. It can take full pathnames and relative pathnames on the command line.
To display the output on screen the –print option must be specified

for operator
The for operator may be used in looping constructs where there is repetitive execution of a section of the shell program.
For var in vall val2 val3 val4;

Do commnds; done

Used to check the file system and repair damaged files. The command takes a device name as an argument
# /etc/fsck /dev/file-system-to-be-checked.

grave operator
Used to store the standard the output of a command in an enviroment variable. (‘)

The grep (global regular expression and print) command can be used as a filter to search for strings in files. The pattern may be either a fixed character string or a regular expression.
Grep “string” filename(s)

User’s home directory

if operator
The if operator allows conditional operator

If expression; then commands; fi
if … then…else… fi
$ if; then

efile; then


used to stop background processes

used to link files. A duplicate of a file is created with another name

displays user’s login name

Lists the files in the current directory

Some of the available options are:
-l gives a long listing
-a displays all file{including hidden files

used to print data on the line printer.
Lp [options] filename(s)

The mesg command controls messages received on a terminal.
-n does not allow messages to be displayed on screen
-y allows messages to be displayed on screen

used to create directories

The more command is used to dispay data one screenful at a time.
More [filename]

Mv (move) moves a file from one directory to another or simply changes filenames. The command takes filename and pathnames as source names and a filename or exiting directory as target names.
mv [source language=”-file”][/source] [target-file]

The news command allows a user to read news items published by the system administrator.

Displays the contents of a file with line numbers

Changes the password

The paste command joins lines from two files and displays the output. It can take a number of filenames as command line arguments.
paste file1 file2

The directories that the system searches to find commands

Used to display data one page (screenful) at a time. The command can take a number of filenames as arguments.
Pg [option] [filename] [filename2]…..

Operator (1) takes the output of one commands as input of another command.

Gives information about all the active processes.

The system prompt

(print working directory) displays the current directory.

The rm (remove) command is used to delete files from a directory. A number of files may be deleted simultaneously. A file(s) once deleted cannot be retrieved.
rm [filename 1] [filename 2]…

sift command
Using shift $1becomes the source string and other arguments are shifted. $2 is shifted to $1,$3to $2 and so on.

The sleep command is used to suspend the execution of a shell script for the specified time. This is usually in seconds.

Sort is a utility program that can be used to sort text files in numeric or alphabetical order
Sort [filename]

Used to split large file into smaller files
Split-n filename
Split can take a second filename on the command line.

Used to switch to superuser or any other user.

Used to copy data in buffers to files

Used to run a UNIX command from within a C program

The tail command may be used to view the end of a file.
Tail [filename]

Used to save and restore files to tapes or other removable media.
Tar [function[modifier]] [filename(s)]

output that is being redirected to a file can also be viewed on standard output.

test command
It compares strings and numeric values.
The test command has two forms : test command itself If test ${variable} = value then
Do commands else do commands

The test commands also uses special operators [ ]. These are operators following the of are interpreted by the shell as different from wildcard characters.
Of [ -f ${variable} ]

Do commands
[ -d ${variable} ]

do commands

do commands

many different tests are possible for files. Comparing numbers, character strings, values of environment variables.

Used to display the execution time of a program or a command. Time is reported in seconds.
Time filename values

The tr command is used to translate characters.
tr [-option] [string1 [string2]]

Displays the terminal pathname

Used to specify default permissions while creating files.

The uniq command is used to display the uniq(ue) lines in a sorted file.
Sort filename uniq

The operator executes the commands within a loop as long as the test condition is false.

Used to send a message to all users logged in.
# /etc/wall message

the command halts the execution of a script until all child processes, executed as background processes, are completed.

The wc command can be used to count the number of lines, words and characters in a fine.
wc [filename(s)]

The available options are:
wc –[options] [filename]
while operator
the while operator repeatedly performs an operation until the test condition proves false.

$ while
Ø do

Ø done

displays information about all the users currently logged onto the system. The user name, terminal number and the date and time that each user logged onto the system.
The syntax of the who command is who [options]

The write command allows inter-user communication. A user can send messages by addressing the other user’s terminal or login id.
write user-name [terminal number]


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One Comment

  1. I am not really wonderful with English but I get hold this very leisurely to read .

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