Useful Linux/Unix commands


Summary and the usage of the unix/Linux commands.

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Help on any Unix command. RTFM!

man {command} Type “man ls” to read the manual for the ls command.

man {command} > {filename} Redirect help to a file to download.

whatis {command} Give short description of command.

apropos {keyword} Search for all Unix commands that match keyword, eg “apropos file”.

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List a directory

ls {path} It’s ok to combine attributes, eg “ls -laF” gets a long listing of all files with types.

ls {path_1} {path_2} List both {path_1} and {path_2}.

ls -l {path} Long listing, with date, size and permisions.

ls -a {path} Show all files, including important .dot files that don’t otherwise show.

ls -F {path} Show type of each file.
“/” = directory, “*” = executable.

ls -R {path} Recursive listing, with all subdirs.

ls {path} > {filename} Redirect directory to a file.

ls {path} | more Show listing one screen at a time.

dir {path} Useful alias for DOS people, or use with ncftp.

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Change to directory

cd {dirname} There must be a space between.

cd ~ Go back to home directory, useful if you’re lost.

cd .. Go back one directory.

cdup Useful alias, like “cd ..”, or use with ncftp.

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Make a new directory

mkdir {dirname}

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Remove a directory

rmdir {dirname} Only works if {dirname} is empty.

rm -r {dirname} Remove all files and subdirs.
Careful!

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Print working directory

pwd Show where you are as full path.
Useful if you’re lost or exploring.

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Copy a file or directory

cp {file1} {file2}

cp -r {dir1} {dir2} Recursive, copy directory and all subdirs.

cat {newfile} >> {oldfile} Append newfile to end of oldfile.

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Move or rename a file

mv {oldfile} {newfile} Moving a file and renaming it are the same thing.

mv {oldname} {newname}

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Delete a file

rm {filespec} ? and * wildcards work like DOS should. “?” is any character; “*” is any string of characters.

ls {filespec} Good strategy: first list a group to rm {filespec} make sure it’s what’s you think…then delete it all at once.

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Download with zmodem (Use sx with xmodem.)

sz [-a|b] {filename} -a = ascii, -b = binary. Use binary for everything. (It’s the default?)

sz *.zip Handy after downloading with FTP.
Go talk to your spouse while it does it’s stuff.

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View a text file

more {filename} View file one screen at a time.

less {filename} Like more, with extra features.

cat {filename} View file, but it scrolls.

cat {filename} | more View file one screen at a time.

page {filename} Very handy with ncftp.

pico {filename} Use text editor and don’t save.

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Edit a text file.

pico {filename} The same editor PINE uses, so you already know it. vi and emacs are also available.

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Create a text file.

cat > {filename} Enter your text (multiple lines with
enter are ok) and press control-d to save.

pico {filename} Create some text and save it.

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Compare two files

diff {file1} {file2} Show the differences.

sdiff {file1} {file2} Show files side by side.

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Other text commands

grep ‘{pattern}’ {file} Find regular expression in file.

sort {file1} > {file2} Sort file1 and save as file2.

sort -o {file} {file} Replace file with sorted version.

spell {file} Display misspelled words

wc {file} Count words in file.

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Find files on system

find {filespec} Works with wildcards. Handy for snooping.

find {filespec} > {filename} Redirect find list to file. Can be big!

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Make an Alias

alias {name} ‘{command}’ Put the command in ‘single quotes’.
More useful in your .cshrc file.

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Wildcards and Shortcuts

* Match any string of characters, eg “page*” gets page1, page10, and page.txt.

? Match any single character, eg “page?” gets page1 and page2, but not page10.

[...] Match any characters in a range, eg “page[1-3]” gets page1, page2, and page3.

~ Short for your home directory, eg
“cd ~” will take you home, and
“rm -r ~” will destroy it.

. The current directory.

.. One directory up the tree,
eg “ls …”

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Pipes and Redirection You pipe a command to another command, and redirect it to a file.

{command} > {file} Redirect output to a file, eg “ls > list.txt” writes directory to file.

{command} >> {file} Append output to an existing file, eg “cat update >> archive” adds update to end of archive.

{command} < {fil1} Get input from a file, eg “sort < file.txt”

{command} < {file1} > {file2} Get input from file1, and write to file2, eg “sort < old.txt > new.txt” sorts old.txt and saves as new.txt.

{command} | {command} Pipe one command to another, eg
“ls | more” gets directory and sends it to more to show it one page at a time.

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Permissions, important and tricky!

Unix permissions concern who can read a file or directory, write to it, and execute it. Permissions are granted or withheld with a magic 3-digit number. The three digits correspond to the owner (you); the group (?); and the world (everyone else).

Think of each digit as a sum:

execute permission = 1
write permission = 2
write and execute (1+2)= 3
read permission = 4
read and execute (4+1)= 5
read and write (4+2)= 6
read, write and execute (4+2+1)= 7

Add the number value of the permissions you want to grant each group to make a three digit number, one digit each for the owner, the group, and the world. Here are some useful combinations. Try to figure them out!

chmod 600 {filespec} You can read and write; the world can’t. Good for files.

chmod 700 {filespec} You can read, write, and execute; the world can’t. Good for scripts.

chmod 644 {filespec} You can read and write; the world can only read. Good for web pages.

chmod 755 {filespec} You can read, write, and execute; the world can read and execute. Good for programs you want to share, and your
public_html directory.

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Permissions, another way

You can also change file permissions with letters:
u = user (yourself) g = group a = everyone
r = read w = write x = execute

chmod u+rw {filespec} Give yourself read and write permission

chmod u+x {filespec} Give yourself execute permission.

chmod a+rw {filespec} Give read and write permission to everyone.

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System info

date Show date and time.

df Check system disk capacity.

du Check your disk usage and show bytes in each directory.

more /etc/motd Read message of the day, “motd” is a useful alias.

printenv Show all environmental variables (in C-shell% – use “set” in Korn shell$).

quota -v Check your total disk use.

uptime Find out system load.

w Who’s online and what are they doing?

 

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How to Make an Alias

An alias lets you type something simple and do something complex. It’s a shorthand for a command. If you want to type “dir” instead of “ls -l” then type “alias dir ‘ls -l'”. The single quotes tell Unix that the enclosed text is one command.

Aliases are more useful if they’re permanent so you don’t have to think about them. You can do this by adding the alias to your .cshrc file so they’re automatically loaded when you start. Type “pico .cshrc” and look for the alias section and add what you want. It will be effective when you start. Just remember that if you make an alias with the name of a Unix command, that command will become unavailable.

Here are a few aliases from my .cshrc file:

# enter your aliases here in the form:
# alias this means this

alias h history
alias m more
alias q quota -v
alias bye exit
alias ls ls -F
alias dir ls
alias cdup cd ..
alias motd more /etc/motd

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Dotfiles (aka Hidden Files)

Dotfile names begin with a “.” These files and directories don’t show up when you list a directory unless you use the -a option, so they are also called hidden files. Type “ls -la” in your home directory to see what you have.

Some of these dotfiles are crucial. They initialize your shell and the programs you use, like autoexec.bat in DOS and .ini files in  Windows. rc means “run commands”. These are all text files that can be edited, but change them at your peril. Make backups first!

Here’s some of what I get when I type “ls -laF”:

.addressbook my email addressbook.
.cshrc my C-shell startup info, important!
.gopherrc my gopher setup.
.history list of past commands.
.login login init, important!
.lynxrc my lynx setup for WWW.
.ncftp/ hidden dir of ncftp stuff.
.newsrc my list of subscribed newsgroups.
.pinerc my pine setup for email.
.plan text appears when I’m fingered, ok to edit.
.profile Korn shell startup info, important!
.project text appears when I’m fingered, ok to edit.
.signature my signature file for mail and news, ok to edit.
.tin/ hidden dir of my tin stuff for usenet.
.ytalkrc my ytalk setup.

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