Basic Unix Editing Commands

Basic Editing

Editing commands require that you be in command mode. Many of the editing commands have a different function depending on whether they are typed in upper or lower case. Often, editing commands can be preceded by a number to indicate a repetition of the command. 

NOTE: Unless specified otherwise, the instructions in this section assume that you are in the command mode. 

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Deleting characters. To delete a character from a file, move the cursor until it is on the incorrect letter, then type x. The character under the cursor disappears. To remove four characters (the one under the cursor and the next three) type 4x. To delete the character before the cursor, type X (upper case). 

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Deleting words. To delete a word, move the cursor to the first letter of the word and type dw. The command deletes the word and the space following it. To delete three words, type 3dw.

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Deleting lines. To delete a whole line, type dd. The cursor does not have to be at the beginning of the line. dd deletes the entire line containing the cursor and places the cursor at the start of the next line. 2dd deletes two lines.

To delete from the cursor position to the end of the line, type D (upper case).

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 Replacing characters. To replace one character with another, move the cursor to the character to be replaced. Type r, then the replacement character. The new character will appear, and you will still be in command mode.

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Replacing words. To replace one word with another, move to the start of the incorrect word and type cw. The last letter of the word to be replaced will turn into a $. You are now in change mode and may type the replacement. The new text does not need to be the same length as the original. Press ESC to get back to command mode. 3cw allows you to replace three words.

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Replacing lines. To change text from the cursor position to the end of the line, type C (upper case). Type the replacement text and press ESC. Press ESC again to get back to command mode.

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Inserting text. To insert text in a line, position the cursor where the new text should go and type i. Enter the new text. The text is inserted before the cursor. Press ESC to get back to command mode.

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Appending text. To add text to the end of a line, position the cursor on the last letter of the line and type a. Enter the new text. This adds text after the cursor. Press ESC to get back to command mode.

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Opening a blank line. Type o (lower case) to insert, or open, a blank line below the current line. Type O (upper case) to insert a blank line above the current line. Press ESC to get back to command mode. 

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Joining lines. The command J (upper case) lets you join two lines together. Put the cursor on the first line to be joined and type J. 3J lets you join 3 lines together.

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Undoing. Undo your most recent edit by typing u (lower case). U (upper case) undoes all the edits on a single line, as long as the cursor stays on that line. Once you move off a line, you can't use U to restore it.

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Moving Around In a File

These shortcuts, which work in command mode, allow you to move more quickly through a file.

Key(s)	Movement
w	forward word by word
b	backward word by word
$	to end of line
0 (zero)	to beginning of line
H	to top line of screen
M	to middle line of screen
L	to last line of screen
G	to last line of file
1G	to first line of file
ctrl-f	jump forward one screen
ctrl-b	jump backward one screen
ctrl-d	scroll down one-half screen
ctrl-u	scroll up one-half screen

Moving by searching. To move quickly in a file, search for text. In command mode, type a / (slash) followed by the text to search for. Press Return. The cursor moves to the first occurrence of that text. Repeat the search in a forward direction by typing n (lower case), or in a backward direction by typing N (upper case).

General

apropos command

Locate commands by keyword lookup.

exit

Terminate your current session, or shell.

man command

Display the Unix manual page describing a given Unix command.

File System Navigation

cd

Return to your home directory.

cd directory

Change directory to make directory your current directory.

file files

Determine file type.

ls

List the contents of the current directory.

ls names

List the contents of the directories; names can name files and/or directories:

ls -l

. . . in a long format, showing permissions, owner, size, and other file info.

ls -a

. . . all files, including "hidden" files (file names that begin with a dot ".").

ls -R

. . . Recursively, for all subdirectories.

ls -t

. . . in time order (when modified, newest to oldest) rather than in name order.

pwd

Display the name of the current directory, or "print working directory."

File/Directory Manipulation

compress files

Reduces the size of a file.

uncompress files

Restores compressed files to their original form.

cp file1 file2

Copy file(s).

cp files directory

Copy file(s) into a directory.

cp -r dir1 dir2

Copy a directory and, recursively, its subdirectories.

mkdir directory

Create, or "make" a directory.

mv file1 file2

Move a file or, if file1 and file2 are in the same directory, rename a file.

mv files directory

Move files into a directory.

mv dir1 dir2

If directory dir2 exists, move dir1 into dir2; otherwise, rename dir1 as dir2.

rm files

Remove (erase) file(s).

rm -r names

Remove files, directories, and recursively, any subdirectories.

rmdir directory

Remove directory (directory must be empty).

Data Manipulation

cat files

Concatenate file(s); you can use cat to display the contents of a file (this is not advisable if the file is a binary file).

grep "pattern" files

Display all lines in the files that match a pattern.

more files

Display contents of files one screen at a time.

sort files

Order the lines in a file or files alphabetically (this command does not alter the file or files -- it merely displays the sorted output to the screen):

sort -r files

. . . in reverse order.

sort -n files

. . . numerically (puts 2 before 10 instead of after).

Networking/Communications

finger user@umich.edu

Displays information about a U-M user from the U-M Online Directory.

ssh hostname

Connect to a remote host using Secure Shell.

telnet hostname

Connect to a remote host using the telnet protocol.

talk user

Initiate a conversation with another user (end conversation with Control-C); talk works only between machines of the same architecture.

Miscellaneous

!!

Repeat last shell command.

!string

Repeat last shell command that began with string (for example, type "!m" to repeat the last command that began with "m").

cal

Display a calendar of the current month.

cal month year

Display a calendar of the given month and year. Note that the year must be fully qualified, for example, "2003" and not "03."

clear

Clears terminal screen.

date

Display the current local date and time.

who

Display a list of users currently logged in.

Q. What is echo $? Command do?

A. It returns the status of last command run. E.g if we run grep command then if the patter is found in the file it shows 0, pattern not found then 1 and file not found then 2.

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Frequently Used Unix Commands

Unix Command Summary

 

For more documentation on a command, consult a good book, or use the man pages. For example, for more information on grep, use the command man grep.

 

cat  -  for creating and displaying short files

 

This is one of the most flexible Unix commands. We can use to create, view and concatenate files. For our first example we create a three-item English-Spanish dictionary in a file called "dict."

 

   % cat >dict

     red rojo

     green verde

     blue azul

<control-D>

   %

 

<control-D> stands for "hold the control key down, then tap 'd'". The symbol > tells the computer that what is typed is to be put into the file dict. To view a file we use cat in a different way:

 

   % cat dict

     red rojo

     green verde

     blue azul

   %

 

If we wish to add text to an existing file we do this:

   % cat >>dict

     white blanco

     black negro

     <control-D>

   %

 

Now suppose that we have another file tmp that looks like this:

 

   % cat tmp

     cat gato

     dog perro

   %

 

Then we can join dict and tmp like this:

   % cat dict tmp >dict2

 

We could check the number of lines in the new file like this:

 

   % wc -l dict2

8

 

The command wc counts things --- the number of characters, words, and line in a file.

 

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chmod --- change permissions

This command is used to change the permissions of a file or directory. For example to make a file essay.001 readable by everyone, we do this:

 

   % chmod a+r essay.001

 

To make a file, e.g., a shell script mycommand executable, we do this

 

   % chmod +x mycommand

 

Now we can run mycommand as a command.

To check the permissions of a file, use ls -l . For more information on chmod, use man chmod.

 

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cd --- change directory

Use cd to change directory. Use pwd to see what directory you are in.

 

   % cd english

   % pwd

   % /u/ma/siya/english

   % ls

novel poems

   % cd novel

   % pwd

   % /u/ma/siya/english/novel

   % ls

ch1 ch2 ch3 journal scrapbook

   % cd ..

   % pwd

   % /u/ma/siya/english

   % cd poems

   % cd

   % /u/ma/siya

 

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cp --- for copying files

Use cp to copy files or directories.

   % cp foo foo.2

 

This makes a copy of the file foo.

   % cp ~/poems/jabber .

 

This copies the file jabber in the directory poems to the current directory. The symbol "." stands for the current directory. The symbol "~" stands for the home directory.

 

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date --- display date

Use this command to check the date and time.

   % date

Mon May  3 10:25:33 IST 2010

 

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echo --- echo argument

The echo command echoes its arguments. Here are some examples:

 

   % echo this

     this

   % echo $EDITOR

     /usr/local/bin/emacs

   % echo $PRINTER

     b129lab1

 

Things like PRINTER are so-called environment variables. This one stores the name of the default printer --- the one that print jobs will go to unless you take some action to change things. The dollar sign before an environment variable is needed to get the value in the variable. Try the following to verify this:

 

   % echo PRINTER

     PRINTER

 

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ftp --- connect to a remote machine to download or upload files

 

Use ftp to connect to a remote machine, then upload or download files. See also: ncftp

 

Example 1: We'll connect to the machine fubar.net, then change director to mystuff, then download the file homework11:

 

   % ftp solitude

     Connected to fubar.net.

     220 fubar.net FTP server (Version wu-2.4(11) Mon Apr 18 17:26:33 MDT 1994) ready.

   Name (solitude:carlson): jeremy

     331 Password required for jeremy.

   Password:

     230 User jeremy logged in.

   ftp> cd mystuff

     250 CWD command successful.

   ftp> get homework11

   ftp> quit

 

Example 2: We'll connect to the machine fubar.net, then change director to mystuff, then upload the file collected-letters:

 

   % ftp solitude

     Connected to fubar.net.

     220 fubar.net FTP server (Version wu-2.4(11) Mon Apr 18 17:26:33 MDT 1994) ready.

   Name (solitude:carlson): jeremy

     331 Password required for jeremy.

   Password:

     230 User jeremy logged in.

   ftp> cd mystuff

     250 CWD command successful.

   ftp> put collected-letters

   ftp> quit

 

The ftp program sends files in ascii (text) format unless you specify binary mode:

 

   ftp> binary

   ftp> put foo

   ftp> ascii

   ftp> get bar

 

The file foo was transferred in binary mode, the file bar was transferred in ascii mode.

 

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grep --- search file

Use this command to search for information in a file or files. For example, suppose that we have a file dict whose contents are

 

   red rojo

   green verde

   blue azul

   white blanco

   black negro

 

Then we can look up items in our file like this;

   % grep red dict

     red rojo

   % grep blanco dict

     white blanco

   % grep brown dict

   %

 

Notice that no output was returned by grep brown. This is because "brown" is not in our dictionary file.

 

Grep can also be combined with other commands. For example, if one had a file of phone numbers named "ph", one entry per line, then the following command would give an alphabetical list of all persons whose name contains the string "Fred".

 

   % grep Fred ph | sort

     Alpha, Fred: 333-6565

     Beta, Freddie: 656-0099

     Frederickson, Molly: 444-0981

     Gamma, Fred-George: 111-7676

     Zeta, Frederick: 431-0987

 

The symbol "|" is called "pipe." It pipes the output of the grep command into the input of the sort command.

For more information on grep, consult

 

   % man grep

 

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head --- display first part of file

Use this command to look at the head of a file. For example,

 

   % head essay.001

 

displays the first 10 lines of the file essay.001 To see a specific number of lines, do this:

 

   % head -20 essay.001

 

This displays the first 20 lines of the file.

 

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ls --- see what files you have

Use ls to see what files you have. Your files are kept in something called a directory.

 

   % ls

     foo       letter2

     foobar    letter3

     letter1   maple-assignment1

   %

 

Note that you have six files. There are some useful variants of the ls command:

 

   % ls l*

     letter1 letter2 letter3

   %

 

Note what happened: all the files whose name begins with "l" are listed. The asterisk (*) is the " wildcard" character. It matches any string.

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lpr --- standard print command (see also print )

This is the standard Unix command for printing a file. It stands for the ancient "line printer." See

 

   % man lpr

 

for information on how it works. See print for information on our local intelligent print command.

 

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more --- use to read files

More is a command used to read text files. For example, we could do this:

 

   % more poems

 

The effect of this to let you read the file "poems ". It probably will not fit in one screen, so you need to know how to "turn pages". Here are the basic commands:

 

q --- quit more

spacebar --- read next page

return key --- read next line

b --- go back one page

For still more information, use the command man more.

 

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mkdir --- create directory

Use this command to create a directory.

   % mkdir essays

 

To get "into" this directory, do

   % cd essays

 

To see what files are in essays, do this:

   % ls

 

There shouldn't be any files there yet, since you just made it. To create files, see cat or emacs.

 

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mv --- for moving and renaming files

Use this command to change the name of file and directories.

 

   % mv foo foobar

 

The file that was named foo is now named foobar

 

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ncftp --- especially good for downloading files via anonymous ftp.

Use ncftp for anonymous ftp --- that means you don't have to have a password.

 

   % ncftp ftp.fubar.net

     Connected to ftp.fubar.net

   > get jokes.txt

 

The file jokes.txt is downloaded from the machine ftp.fubar.net.

 

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print --- custom print command (see also lpr )

This is a moderately intelligent print command.

   % print foo

   % print notes.ps

   % print manuscript.dvi

 

In each case print does the right thing, regardless of whether the file is a text file (like foo ), a postcript file (like notes.ps, or a dvi file (like manuscript.dvi. In these examples the file is printed on the default printer. To see what this is, do

 

 

   % print

 

and read the message displayed. To print on a specific printer, do this:

   % print foo jwb321

   % print notes.ps jwb321

   % print manuscript.dvi jwb321

 

To change the default printer, do this:

   % setenv PRINTER jwb321

 

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pwd --- find out what directory you are in

Use this command to find out what directory you are working in.

   % pwd

/u/ma/jeremy

   % cd homework

   % pwd

/u/ma/jeremy/homework

   % ls

assign-1 assign-2 assign-3

   % cd

   % pwd

/u/ma/jeremy

   %

 

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rm --- remove a file

Use rm to remove files from your directory.

   % rm foo

     remove foo? y

   % rm letter*

     remove letter1? y

     remove letter2? y

     remove letter3? n

   %

 

The first command removed a single file. The second command was intended to remove all files beginning with the string "letter." However, our user (Jeremy?) decided not to remove letter3.

 

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rmdir --- remove directory

Use this command to remove a directory. For example, to remove a directory called "essays", do this:

 

   % rmdir essays

 

A directory must be empty before it can be removed. To empty a directory, use rm.

 

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rsh --- remote shell

Use this command if you want to work on a computer different from the one you are currently working on. One reason to do this is that the remote machine might be faster. For example, the command

 

   % rsh solitude

 

connects you to the machine solitude. This is one of our public workstations and is fairly fast.

 

See also: telnet

 

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setenv --- set an environment variable

   % echo $PRINTER

     labprinter

   % setenv PRINTER myprinter

   % echo $PRINTER

     myprinter

 

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sort --- sort file

Use this commmand to sort a file. For example, suppose we have a file dict with contents

red rojo

green verde

blue azul

white blanco

black negro

 

Then we can do this:

   % sort dict

     black negro

     blue azul

     green verde

     red rojo

     white blanco

 

Here the output of sort went to the screen. To store the output in file we do this:

   % sort dict >dict.sorted

 

You can check the contents of the file dict.sorted using cat , more , or emacs .

 

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tail --- display last part of file

Use this command to look at the tail of a file. For example,

 

   % head essay.001

 

displays the last 10 lines of the file essay.001 To see a specific number of lines, do this:

 

   % head -20 essay.001

 

This displays the last 20 lines of the file.

 

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tar --- create an archive, add or extract files

Use create compressed archives of directories and files, and also to extract directories and files from an archive. Example:

 

   % tar -tvzf foo.tar.gz

 

displays the file names in the compressed archive foo.tar.gz while

 

   % tar -xvzf foo.tar.gz

 

extracts the files.

 

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telnet --- log in to another machine

Use this command to log in to another machine from the machine you are currently working on. For example, to log in to the machine "solitude", do this:

 

   % telnet solitude

 

See also: rsh.

 

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top --- display the most resource consuming processes in the below format

 

CPU TTY  PID USERNAME PRI NI   SIZE    RES STATE    TIME %WCPU  %CPU COMMAND

 0   ? 19984 root     240 20  2268K   576K run      0:33 28.76 28.71 gzip

 

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wc --- count characters, words, lines

Use this command to count the number of characters, words, and lines in a file. Suppose, for example, that we have a file dict with contents

 

red rojo

green verde

blue azul

white blanco

black negro

 

Then we can do this

   % wc dict

     5      10      56  dict

 

This shows that dict has 5 lines, 10 words, and 56 characters.

 

The word count command has several options, as illustrated below:

 

   % wc -l dict

     5 dict

   % wc -w dict

     10 dict

   % wc -c dict

     56 dict

 

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Unix Shell Scripting Interview Questions - 1

• How do you find out what’s your shell? - echo $SHELL
• What’s the command to find out today’s date? - date
• What’s the command to find out users on the system? - who
• How do you find out the current directory you’re in? - pwd
• How do you remove a file? - rm
• How do you remove a - rm -rf
• How do you find out your own username? - whoami
• How do you send a mail message to somebody? - mail somebody@mindgrillq.com -s ‘Your subject’ -c ‘cc@mindgrillq.com‘
• How do you count words, lines and characters in a file? - wc
• How do you search for a string inside a given file? - grep string filename
• How do you search for a string inside a directory? - grep string *
• How do you search for a string in a directory with the subdirectories recursed? - grep -r string *
• What are PIDs? - They are process IDs given to processes. A PID can vary from 0 to 65535.
• How do you list currently running process? - ps
• How do you stop a process? - kill pid
• How do you find out about all running processes? - ps -ag
• How do you stop all the processes, except the shell window? - kill 0
• How do you fire a process in the background? - ./process-name &
• How do you refer to the arguments passed to a shell script? - $1, $2 and so on. $0 is your script name.
• What’s the conditional statement in shell scripting? - if {condition} then … fi
• How do you do number comparison in shell scripts? - -eq, -ne, -lt, -le, -gt, -ge
• How do you test for file properties in shell scripts? -
  -s filename tells you if the file is not empty,
  -f filename tells you whether the argument is a file, and not a directory,
  -d filename tests if the argument is a directory, and not a file,
  -w filename tests for writeability,
  -r filename tests for readability,
  -x filename tests for executability
• How do you do Boolean logic operators in shell scripting?
  - ! tests for logical not,
  -a tests for logical and, and
  -o tests for logical or.
• How do you find out the number of arguments passed to the shell script? - $#
• What’s a way to do multilevel if-else’s in shell scripting?
  - if {condition} then {statement} elif {condition} {statement} fi
• How do you write a for loop in shell? - for {variable name} in {list} do {statement} done
• How do you write a while loop in shell? - while {condition} do {statement} done
• How does a case statement look in shell scripts?
  - case {variable} in {possible-value-1}) {statement};; {possible-value-2}) {statement};; esac
• How do you read keyboard input in shell scripts? - read {variable-name}
• How do you define a function in a shell script? - function-name() { #some code here return }
• How does getopts command work?
  - The parameters to your script can be passed as -n 15 -x 20. Inside the script, you can iterate through the getopts array as while getopts n:x option, and the variable $option contains the value of the entered option.

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