The following is a quick overview of essential UNIX commands.
ls –ld directory
List directory contents
List permissions on directory
|pwd||pwd||Display current directory|
cp source target
cp –r source target
Copy file source to target
Copy directory, recursive copy
|mv||mv source target||Move file or directory from source to target (the source is removed after the move)|
rm –f filename
rm –rf directory
Remove a file
Remove a file in which you have directory write privileges but not file write privileges
Remove non-empty directory
|mkdir||mkdir directory||Create a directory|
|rmdir||rmdir directory||Remove empty directory|
ps –u userid
Display process statuses
Display all processes
Display all process for userid
kill -9 PID
Terminate process with process ID (PID). Sends UNIX process the TERM signal. This signal should terminate most UNIX processes.
Terminate process with PID. Sends UNIX process the KILL signal. This should only be used when normal attempts to terminate the process are ineffective.
grep pattern filename
grep –l pattern filename(s)
Display all occurrences of pattern in filename
Display all filename(s) containing pattern
cat file file2
cat file1 file2>file3
Display contents of filename
Display contents of file1 and file2
Create file3 from contents of file1 and file2
|more||more filename||Display file contents, one page at a time|
|man||man command||Display UNIX man(ual) page for given command|
tar tvf tarfile.tar
tar xvf tarfile.tar
tar cvf tarfile.tar*
Display contents of tarfile
Extract contents of tarfile
Create tarfile named tarfile.tar with all files and directories in the current directory
|chmod||chmod 755 directory||Change file or directory permissions|
|gunzip||gunzip file.gz||Uncompress .gz file (generally used with tarfiles). If it is not in your path, check /vol.nsm/tools/bin.|
|vi||vi file||Edit file|
|find||find / -name file||Locate file starting in root (/) directory|
|exit||exit||Logout of your UNIX session|
|id||id||Display user name, user ID, and primary group ID|
-- or --
-- or --
|Display all UNIX groups to which you belong|
-- or --
-- or --
|Display the hostname of the UNIX machine|
|passwd||passwd||Change your UNIX password|
|env||env||Display your environment variables|
|nohup||nohup command &||Execute command in the background, and do not terminate the process if you logout of your UNIX session.|
|command &||command &||Execute the command in the background. Output will be sent to a file named nohup.out rather than your display.|
|jobs||jobs||List background processes|
|Ctrl-Z and bg||Suspend current foreground process, put process in background for execution|
|gzip||gzip filename||Compress file (generally used with tarfiles)|
File and Directory Permissions Demystified
When doing a long listing (ls –l) of a directory, we see the following entry:
drwxr-xr-x 2 hutchib nsm 512 Apr 20 11:09 bin
This is a directory named bin that is owned by user hutchib and group nsm. Let's explore the first 10 characters in detail.
- The first character is a d, which indicates that we are looking at a directory. Other possibilities for the first character include an - for an ordinary file and an l for a symbolic link (like a shortcut in Windows).
- Characters 2 through 4 correspond to user permissions, or permissions corresponding to the owner of the directory. They are rwx, which indicates that the directory is readable, writable, and executable by the user (the owner of the directory, hutchib).
- Characters 5 through 7 correspond to group permissions. In this example, these permissions apply to the group nsm. They are r-x, indicating that the directory is readable and executable by any user belonging to group nsm.
- Characters 8 through 10 correspond to other permissions. If you are not the owner of the directory, nor a member of the group, the other permissions are applicable. They are r-x, meaning that the directory is readable and executable by everyone else.
What do read, write, and execute permissions mean on a directory?
Read = You are able to list contents of the directory and display contents of files.
Write = You are able to create, modify, or delete files in the directory.
Execute = You are able to change into the directory. (Even if
you had read and write privileges
on a directory, if you do not have execute privileges on the directory, you would not be able to get into (cd) the directory.)
Note: If you have write privileges to a directory, you may delete any file in that directory, even if it is not writable, and is owned by somebody else.
What do read, write, and execute permissions mean on a file?
Read = You are able to list the contents of a file.
Write = You are able to modify or delete the file. (If you have
permission to write to a file, you
may modify it, but may not delete it, if the directory is not writable.)
Execute = You are able to execute the file. (This is needed if the file is a shell script or Executable.)
How do I change file/directory permissions?
You may change file and directory permissions with the chmod command.
The syntax is:
chmod octal-mode file_or_directory
You may recursively change permissions with the chmod –R command.
When looking at the following table, remember these values when setting file or directory permissions:
Read = 4
Write = 2
Execute = 1
User: rwx = 4 + 2 + 1 = 7
Group: rwx = 4 + 2 + 1 = 7
Other: rwx = 4 + 2 + 1 = 7
|777||chmod 777 file_or_directory|
User: rwx = 4 + 2 + 1 = 7
Group: r-x = 4 + 1 = 5
Other: r-x = 4 + 1 = 5
|755||chmod 755 file_or_directory|
User: rw- = 4 + 2 = 6
Group: r-- = 4
Other: r-- = 4
|644||chmod 644 file_or_directory|
Useful 'vi' Commands for Vim Text Editor
The vi editor has two modes: Input and Command. In Input mode, any characters you type will be entered into the text file. In Command mode, characters you type are used to move around the screen and modify the file. If you are unsure which mode you are in, press Esc, and you will be put into Command mode.
|h||Move cursor one position left|
|j||Move cursor one position down|
|k||Move cursor one position up|
|l||Move cursor one position right|
|:1||Go to beginning of file|
|G||Go to bottom of file|
|0||Go to beginning of line|
|$||Go to end of line|
|i||Insert text before cursor|
|a||Append text after cursor|
|A||Append text at end of line|
|Esc||Enter command mode|
|:w||Save the file, continue working|
|:wq||Save the file and exit|
|:q!||Exit without saving|
|:%s/search/replace/g||Replace all occurrences of search with replace within the file|
File Extension Primer
|.tar.gz||File was archived with tar and compressed with the gzip command. Use gunzip to uncompress it, then tar xvf filename.tar to extract it. (If gunzip is not in your path, you may find it in /vol.nsm/tools/bin)|
|.gz||File was compressed with the gzip command. Use gunzip to uncompress it.|
|.Z||File was compressed with the compress command. Use uncompress to uncompress it.|
|.zip||File was compressed with the zip command. Use unzip to uncompress it.|
You can use the UNIX command file to attempt to determine the file type.
$ file /home/hutchib/long_cmd.sh
/home/hutchib/long_cmd.sh: executable shell script
$ file /usr/bin/ls
/usr/bin/ls: ELF 32-bit MSB executable SPARC Version 1, dynamically linked, stripped
How do I redirect command output?
Generally, output of your UNIX commands is sent to standard output (STDOUT). You may redirect command output to a file by using:
command > file
If file does not exist, it will be created. If file already exists, it will be overwritten. You could instead append to the end of file by using:
command >> file
In addition to standard output, UNIX has a mechanism called standard error (STDERR). It is sometimes useful to discard standard error when performing commands. For example, when executing a find command on a UNIX system, you normally don't want to see permission denied messages when find attempts to read directories you don't have access to. The following command would redirect standard error to /dev/null, effectively discarding the output:
If you absolutely do not want the command to generate any output (e.g. a crontab entry), use the following command to send both standard output and standard error to /dev/null:
command >/dev/null 2>&1
How do I put a process in the background?
Z + Stopped (SIGTSTP) long_cmd.sh
$ bg %1
 + Running long_cmd.sh
$ fg %1
Execute a shell script called long_cmd.sh, which will take several minutes to complete. Since no interaction with the terminal can occur while this script is executing, press Ctrl-Z to suspend the script. After suspending the script, put it in the background with the bg %1 command. List the background processes with the jobs command. The background process will continue to execute and will complete; the shell will notify you when the job has completed. For this example, you can put the job back in the foreground with the fg %1 command.