Navigating the File System

Let's learn some commands on navigating the file system.

The LS command

ls- lists the contents of the current directory or can also be used to list the contents of any other directory.

By default, the list is sorted alphabetically by name.

e.g. ls /

will list the contents of the root directory (/ indicates the root directory)

ls can be used to list the contents of multiple directories, by separating each directory with a space.

e.g. ls ~ Sweta

will list the contents of my home directory (indicated by ~) and that of user Sweta. Note what the output looks like

/home/me:

Aditya nick ranin Shraddha Sweta

Sweta:

CAT NOD

Options

Note that some commands in Linux support options that alter the behavior of the command. We will discuss the options with the list (ls) command below.

-l

can be used to display the output in a long format so that you can view more details about the directories and files. See what the output looks like below :

total 20

drwxrwxr-x 2 app_etlmgmt_qa app_etlmgmt_qa 4096 Aug 18 15:00 Aditya

drwxrwxr-x 2 app_etlmgmt_qa app_etlmgmt_qa 4096 Aug 11 10:08 nick

drwxrwxr-x 4 app_etlmgmt_qa app_etlmgmt_qa 4096 Aug 15 11:25 ranin

drwxrwxr-x 3 app_etlmgmt_qa app_etlmgmt_qa 4096 Aug 17 16:15 Shraddha

drwxrwxr-x 4 app_etlmgmt_qa app_etlmgmt_qa 4096 Aug 11 14:05 Sweta

will display the contents of the current working directory, in a long (l) format including permissions, owners, groups, size and creation date of files and folders, sorted by the file's modification time (t) in reverse order (--reverse).

e.g. ls -l ./

total 8

drwxr-xr-x. 2 user user 6 Jan 7 2015

Desktop

-rw-rw-r--. 1 user user 431 Aug 6 2015 VNCHOWTO

-rw-------. 1 user user 68 Mar 18 2016 xrdp-chansrv.log

Note we have the permissions, owners, groups, size and creation date of each of the files and folders in the list.

Compare the above output to only the 'ls' command

$ ls ./

Desktop VNCHOWTO xrdp-chansrv.log

-a / --all

List all files, even those with names that begin with a period, which are normally not listed (i.e., hidden).

-R

The capital R flag is used to list the contents of a directory recursively such that all files under the current folder and under all the subfolders are listed.

In order to test how the recursive command works, I created a folder structure like this with some files under it. Note directories are indicated by the - sign.

-rbTest1

rbTestFile

-rbTest2

rbTestFile2

-rbTest21

rbTestFile21

Now when I use the -R option (along with the -p option so that I can easily identify directories), this is the result I get :

$ ls -pR

.:

Desktop/ rbTest1/ rbTest2/ VNCHOWTO xrdp-chansrv.log

./Desktop:

./rbTest1: rbTestFile

./rbTest2: rbTest21/ rbTestFile2

./rbTest2/rbTest21: rbTestFile21

Note how you can see the entire structure of the directory from the current directory all the way until the bottom level.

Wildcards

Note you can use wildcards with the ls command to filter the list of files and folders to those whose names match a specific pattern. For e.g. if you only wanted to list the contents of only those files and folders that begin with the pattern "rb", you would use the command: ls rb*

-S

Sort results by file size.

-t

Sort by modification time.

-p

This option appends an indicator to folders (the indicator is a forward slash /).

e.g. $ ls

Output : Desktop VNCHOWTO xrdp-chansrv.log

In the results above, we can't tell which of the items are files and which ones are folders.

$ ls -p

Output : Desktop/ VNCHOWTO xrdp-chansrv.log

Now with the -p option, the "Desktop" item has a forward slash appended to it, indicating that it is a folder. The rest of the items are files.

Similarly some command options use the entire word spelled out preceeded by two dashes e.g. ls --reverse will reverse the order of the sort. Also commands support multiple options to be strung together e.g. ls -lt where the t options sorts the output by the file's modification time.

ls -lt --reverse

Will display the list of files and folders sorted in reverse order by file's modification time

-h / --human-readable

In long format listings, displays file sizes in human-readable format rather than in bytes.

Note the difference in the output between ls -lh and ls -l

ls -lh

drwxrwxr-x 2 app_etlmgmt_qa app_etlmgmt_qa4.0KAug 18 15:00 Aditya

drwxrwxr-x 2 app_etlmgmt_qa app_etlmgmt_qa4.0KAug 11 10:08 nick

ls -l

drwxrwxr-x 2 app_etlmgmt_qa app_etlmgmt_qa4096Aug 18 15:00 Aditya

drwxrwxr-x 2 app_etlmgmt_qa app_etlmgmt_qa4096Aug 11 10:08 nick

The File command

To get more information about a file's type, we use the file command

e.g. file test.jpg

could give you the following output :

test.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, baseline, precision 8, 1280x5859, frames 3

The PWD command

pwd- prints the name of the current working directory

The CD command

cd- used to change the directory

cd can also be used to navigate up the directory structure using relative paths. cd .. takes you to the parent directory of your current directory cd ../../ takes you two levels up. A sngle dot . represents the current directory

Note that as you change your current directory, the shell prompt changes accordingly to show your current working directory.

Some shortcuts to change the current working directory:

IMPORTANT FACTS ABOUT FILENAMES

• Filenames that begin with a period character are hidden. This only means thatlswill not list them unless you sayls -a. When your account was created, several hidden files were placed in your home directory to configure things for your account. Later on we will take a closer look at some of those files to see how you can customize your environment. In addition, some applications place their configuration and settings files in your home directory as hidden files.

• Filenames and commands in Linux, as in Unix, are case sensitive. The filenames_File1_and_file1_refer to different files.

• Linux has no concept of a “file extension” like some other operating systems. You may name files any way you like. The contents and/or purpose of a file is determined by other means. Although Unix-like operating systems don’t use file extensions to determine the contents/purpose of files, some application programs do.

• Though Linux supports long filenames that may contain embedded spaces and punctuation characters, limit the punctuation characters in the names of files you create to period, dash (hyphen), and underscore.Most importantly, do not embed spaces in filenames. Embedding spaces in filenames will make many command line tasks more difficult

The CP command

This is the Copy command.

The cp command copies files or directories. It can be used two different ways:

cp item1 item2

to copy the single file or directory item1 to file or directory item2 and:

cp item... directory

to copy multiple items (either files or directories) into a directory.

Some common options used with the copy command (with the long and short equivalent) :

-a, --archive

Copy the files and directories and all of their attributes, including ownerships and permissions. Normally, copies take on the default attributes of the user performing the copy.

-i, --interactive

Before overwriting an existing file, prompt the user for confirmation. If this option is not specified, cp will silently overwrite files.

-r, --recursive

Recursively copy directories and their contents. This option (or the -a option) is required when copying directories.

-u, --update

When copying files from one directory to another, copy only files that either don’t exist or are newer than the existing corresponding files in the destination directory.

-v, --verbose

Display informative messages as the copy is performed.

Some examples:

cp file1 file2

Copy file1 to file2. If file2 exists, it is overwritten with the contents of file1. If file2 does not exist, it is created.

cp -i file1 file2

Same as above, except that if file2 exists, the user is prompted before it is overwritten.

cp file1 file2 dir1

Copy file1 and file2 into directory dir1. dir1 must already exist.

cp dir1/* dir2

Using a wildcard, all the files in dir1 are copied into dir2. dir2 must already exist.

cp -r dir1 dir2

Copy directory dir1 (and its contents) to directory dir2. If directory dir2 does not exist, it is created and will contain the same contents as directory dir1.