Unix Basics 1

This exercise is designed to provide the basic skills required for working in the UNIX environment, using plenty of relevant examples, specifically for biologists. If you are using your personal computer, make sure that you have downloaded the files required for the workshop. This exercise will provide you information regarding navigation, files and directory creation/modification and some administrative things related to file permissions.

Getting started

The data files required for this workshop can be found on our website. You need to download this and place it in your home directory (/home/username), before you start this exercise. Please use the commands below to get started (you will learn what these command does later in the exercise). Open the terminal and enter these commands (commands are case sensitive) and each command should be entered in a single line followed by ↵ (Enter) key.

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cd ~
curl -O http://gif-server.biotech.iastate.edu/arnstrm/WORKSHOP_FILES.tar.gz

Once your cursor (command prompt) comes back to the original position, type

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tar xf WORKSHOP_FILES.tar.gz
ls

You should see WORKSHOP_FILES listed there.

PS: all materials, including the slides, handout and instructions to set up your computer should be in the folder you downloaded.

This section will introduce you to some basic file/directory navigation and manipulation techniques.

To know the present location

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pwd

Returns you the present working directory (print working directory)

You should see the output something like /home/username This means, you are now working in the username directory, which is located in home directory. The directory that you will be in after logging in is your home directory. You can also avoid writing the full path by using ~ in front of your username or simply ~

~ or ~username same as /home/username

Present directory is represented as . (dot) and parent directory is represented as .. (dot dot).

Changing directories

To jump from one directory to another we use the cd (change directory) command.

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cd ..

Changes your present location to the parent directory

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cd DIRECTORY

This changes your location back to your DIRECTORY.

Task 1.1: Change your directory to the WORKSHOP_FILES directory present in your home directory.

TIP: You can type in first few letters of the directory name and then press Tab to auto complete rest of the name (especially useful when the file/directory name is long). This only works when there are unique matches for the starting letters you have typed. If there is more than one matching files/directories, pressing Tab twice will list all the matching names. You can also recall your previous commands by pressing ↑ or ↓ arrow keys or browse all your previously used commands by typing history on your terminal (typically, last 500 commands will be saved in this file).

Directories and files

Making directories

To create a directory, mkdir (make directory) can be used.

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mkdir DIRECTORY

Unlike PC/Mac folders, here you can’t have space in your directory name (but some special characters are okay). You can also specify the path where you want to create your new folder.

Task 1.2: Make a new directory named FirstDirectory within the WORKSHOP_FILES directory. Then change your directory to the FirstDirectory.

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mkdir FirstDirectory

Copying directories

To copy a file, cp (copy) command is used. When using this command you have to provide both source file and destination file.

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cp SOURCE DESTINATION

You can also specify the absolute path of the source and/or destination file. To know more about any command you can use man command, which opens the manual of the command you ask (referred as man page).

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man cp

This opens the manual for the cp command. Take a look at the manual of cp command (use arrow keys to move top or bottom of the page). OPTIONS are arguments that can be used to accomplish more from the same command (and are not required for regular operation). Eg., by using option –i with the regular cp command, you can always make sure that you are not overwriting the existing file while copying (if the target already contains the same file). The syntax for using the options will also be provided in the manual. To exit, press q*.

Looking at the man page for cp command, what options can be used to copy a directory (including all files within it)?

How else you can get help on cp command (other than ‘man’)?

Task 1.3: Now change your directory back to the home directory. Create a copy of WORKSHOP_FILES and name it as BACKUP_WORKSHOP). This will serve as a backup copy of all files that are required for the workshop (in case you accidentally modify the contents while working).

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cp -r WORKSHOP_FILES BACKUP_WORKSHOP

Moving directories

To move a file or a directory, mv (move) command is used. Again, like the cp command you need to provide both source file and destination file.

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mv SOURCE DESTINATION

Absolute path also works fine. Some of the options used by cp command also work with mv command. mv can also be used to rename files and directories

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mv OLDNAME NEWNAME

Task 1.4: Rename WORKSHOP_FILES as tutorials.

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mv WORKSHOP_FILES tutorials

Viewing the contents of the directory

The contents of a directory can be viewed using ls (list) command.

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ls DIRECTORY

If no directory name is provided then ls will list all the contents of the present directory. Like any other command, you can use absolute path or abbreviated path. There are also various options available for ls command. Some very useful options include:

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ls –l #Lists all the files in lengthy or detailed view
ls –t #Lists all the files, sorted based on creation time
ls –S #Lists all the files, sorted based on size

You can also combine these options together for getting more focused results.

Looking at the manual for ls, what option can you use to view hidden files in a directory (files starting with dot)?

Can you sort the files based on its extension? How?

Task 1.5: Examine the contents of the tutorials directory. Try options such as -l, -t, -a and -X. Also check if you can combine many options together (like -la or -lh etc). Try these:

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ls -l tutorials
ls -a
ls -1 tutorials
ls -lh tutorials
ls -t tutorials

Creating and editing files

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touch FILENAME

Creates a new file in the present location

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nano FILENAME

Like notepad/textedit, this text editor lets you edit a file.

Task 1.6: Create a new file named firstfile inside the tutorials directory. You can create using touch or using nano. Then add some contents (Your name and email address) to the firstfile (using nano). After editing, press Ctrl + X to exit, then enter y to save changes and confirm the file name.

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touch firstfile
nano firstfile

Viewing contents of the files

Moving directories

To move a file or a directory, mv (move) command is used. Again, like the cp command you need to provide both source file and destination file.

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mv SOURCE DESTINATION

Absolute path also works fine. Some of the options used by cp command also work with mv command. mv can also be used to rename files and directories

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mv OLDNAME NEWNAME

Task 1.4: Rename WORKSHOP_FILES as tutorials.

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mv WORKSHOP_FILES tutorials

Viewing the contents of the directory

The contents of a directory can be viewed using ls (list) command.

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ls DIRECTORY

If no directory name is provided then ls will list all the contents of the present directory. Like any other command, you can use absolute path or abbreviated path. There are also various options available for ls command. Some very useful options include:

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ls –l #Lists all the files in lengthy or detailed view
ls –t #Lists all the files, sorted based on creation time
ls –S #Lists all the files, sorted based on size

You can also combine these options together for getting more focused results.

Looking at the manual for ls, what option can you use to view hidden files in a directory (files starting with dot)?

Can you sort the files based on its extension? How?

Task 1.5: Examine the contents of the tutorials directory. Try options such as -l, -t, -a and -X. Also check if you can combine many options together (like -la or -lh etc). Try these:

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ls -l tutorials
ls -a
ls -1 tutorials
ls -lh tutorials
ls -t tutorials

Creating and editing files

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touch FILENAME

Creates a new file in the present location

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nano FILENAME

Like notepad/textedit, this text editor lets you edit a file.

Task 1.6: Create a new file named firstfile inside the tutorials directory. You can create using touch or using nano. Then add some contents (Your name and email address) to the firstfile (using nano). After editing, press Ctrl + X to exit, then enter y to save changes and confirm the file name.

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touch firstfile
nano firstfile

Viewing contents of the files

There are various commands to print the contents of the file in bash. Most of these commands are often used in specific contexts. All these commands when executed with filenames displays the contents on the screen. Most common ones are less, more, cat, head and tail

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less FILENAME
#try this:
less AT_cDNA.fa

Displays file contents on the screen with line scrolling (to scroll you can use arrow keys, PgUp/PgDn keys, space bar or Enter key).

When you are done press q to exit.

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more FILENAME
# try this:
more AT_cDNA.fa

Like less command, more also displays file contents on the screen with line scrolling, but uses only space bar or Enter key to scroll.

When you are done press q to exit.

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cat FILENAME
try this:
cat AT_cDNA.fa

Simplest form of displaying contents. It catalogs the contents of the file on the screen. In case of large files, entire file will scroll on the screen without pausing

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head FILENAME
# try this:
head AT_cDNA.fa

Displays only the starting lines of a file. The default is first ten lines. But any number of lines can be displayed using –n option (followed by required number of lines).

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tail FILENAME
try this:
tail AT_cDNA.fa

Similar to head, but displays the last 10 lines. Again –n option can be used to change this.

More information about any of these commands can be found in man pages (man command)

Task 1.7: Try using all these commands on the RefSeq.faa. You are also welcome to try these commands on various other files that are present in the tutorials directory. These commands don’t change the contents of the file; they just display them on the screen.

Deleting files and directories

To delete directories from the system, you can use rmdir (remove directory) command. You can also use rm command to delete file(s).

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rmdir DIRECTORY

The directory should be empty before you use the rmdir command.

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rm FILE

To delete a file rm command can be used Some useful options include : –r recursively delete files, -f delete forcefully

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rm –rf DIRECTORY  [DO NOT USE THIS NOW!]

When you want to delete a folder, with all its content

Task 1.8: Delete the directory named delete_me inside the tutorials directory (to do this you may first want to delete the sample.txt file inside this directory).

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cd delete_me
rm sample.txt
cd ..
rmdir delete_me

Compression/Decompression

There are several options for archiving and compressing groups of files or directories. Compressed files are not only easier to handle (copy/move) but also occupy less size on the disk (less than 1/3 of the original size). In Linux systems you can use zip, tar or gz for archiving and compressing files/directories.

zip

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zip OUTFILE.zip INFILE.txt

Compress INFILE.txt

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zip -r OUTDIR.zip DIRECTORY

Compress all files in a DIRECTORY into one archive file (OUTDIR.zip)

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zip -r OUTFILE.zip . -i *.txt

Compress all txt files in a DIRECTORY into one archive file (OUTFILE.zip)

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unzip SOMEFILE.zip

Decompress a file Task 1.9: Zip AT_genes.gff file located in the tutorials directory. Check the file size before and after zip compression (Hint: use ls command with special options to check file sizes).

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zip AT_genes.gff.zip AT_genes.gff

Is there any size difference before and after compressing?

tar

tar (tape archive) utility saves many files together into a single archive file, and restores individual files from the archive. It also includes automatic archive compression/decompression options and special features for incremental and full backups.

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tar -cvf OUTFILE.tar INFILE

archive INFILE

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tar -czvf OUTFILE.tar.gz INFILE

archive and compress file INFILE

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tar -tvf SOMEFILE.tar

list contents of archive SOMEFILE.tar

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tar -xvf SOMEFILE.tar

extract contents of SOMEFILE.tar

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tar -xzvf SOMEFILE.tar.gz

extract contents of gzipped archive SOMEFILE.tar.gz

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tar -czvf OUTFILE.tar.gz DIRECTORY

archive and compress all files in a directory into one archive file

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tar -czvf OUTFILE.tar.gz *.txt

archive and compress all “.txt” files in current directory into one archive file

Task 1.10: Archive and compress the BACKUP_WORKSHOP directory you created in Task 1.3 (you can name it as backup.tar.gz or anything you want)

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tar -czvf backup.tar.gz BACKUP_WORKSHOP

gzip

gzip (gnu zip) compression utility designed as a replacement for zip, with much better compression and no patented algorithms. The standard compression system for all GNU software.

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gzip SOMEFILE

compress SOMEFILE (also removes uncompressed file)

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gunzip SOMEFILE.gz

uncompress SOMEFILE.gz (also removes compressed file)

Task 1.11: gzip the file AT_genes.gff and examine the size. gunzip it back so that you can use this file for the later exercises.

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gzip AT_genes.gff
ls -lh
gunzip AT_genes.gff.gz
ls –lh

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