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Excerpt
nameStarting Shell Access in OnDemand
Click shell.pngImage RemovedClick shell.pngImage Added

image-20240731-224939.pngImage Removed

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The Command-Line Prompt

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Your Prompt

Note

From now on, your prompt will take the form: [<username>@<hostname> ~]$

where:

  • <username> is YOUR username or potentially arcc-txx if you are using a training account.

  • <hostname> will take the form of mblog1, mblog2 - it should have log within the name to indicate you are using a login node - this will be covered within the Intro to HPC workshop, specifically What is HPC?

...

Syntax of a Shell Command

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Linux IS Case Sensitive

Info

In Linux, commands, options, folder, filenames… are Case Sensitive.

Code Block
# Lists what is in the current location.
[arcc-t05@blog1<username>@<hostname> ~]$ ls
Desktop  Documents  Downloads
# Throws an error.
[arcc-t05@blog1<username>@<hostname> ~]$ LS
-bash: LS: command not found
Filename  ≠  FiLeNaMe  ≠  FILENAME
Note
Code Block

 

...

Remember: Filename 

≠ 

FiLeNaMe 

≠ 

FILENAME

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Getting Help: man

Info

Linux has a number of ways to find help on commands. The first is man - “manual”.

Code Block
[arcc-t05@blog1<username>@<hostname> ~]$ man ls
LS(1)                                     User Commands                                     LS(1)
NAME
       ls - list directory contents
SYNOPSIS
       ls [OPTION]... [FILE]...
DESCRIPTION
       List  information about the FILEs (the current directory by default).  Sort entries alpha‐
       betically if none of -cftuvSUX nor --sort is specified.
       Mandatory arguments to long options are mandatory for short options too.
       -a, --all
              do not ignore entries starting with .
       -A, --almost-all
              do not list implied . and ..
       ...
Manual page ls(1) line 1 (press h for help or q to quit)

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Getting Help: <command --help>

Info

The next method is to use a command's --help option.

Code Block
[arcc-t05@blog1<username>@<hostname> ~]$ ls --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.
Mandatory arguments to long options are mandatory for short options too.
  -a, --all                  do not ignore entries starting with .
  -A, --almost-all           do not list implied . and ..
      --author               with -l, print the author of each file
  -b, --escape               print C-style escapes for nongraphic characters
      --block-size=SIZE      with -l, scale sizes by SIZE when printing them;
                               e.g., '--block-size=M'; see SIZE format below
  -B, --ignore-backups       do not list implied entries ending with ~
...

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Getting Help: Options

Info

Typically, options can have a:

  • short-name: “-a”:

    • Single letter following a single “-”

  • long-name: “--all”: 

    • More descriptive word after two dashes “--”

Short options can be grouped: 

  • “ls -a –l” can be shortened to “ls –al”

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Single vs Multiple Lines

Info
Code Block
[arcc-t05@blog1

If you have a long command, which is difficult to read over a single line, you can split it up across multiple lines.

To split, at the end of the line where you want to split type \ followed by ENTER, and you’ll see that me move to the next line as indicated by the >.

You can continue to split across multiple lines.

Once you’re ready to execute, simply press ENTER (without the \ character).

Code Block
[<username>@<hostname> ~]$ ls -al ~

[arcc-t05@blog1<username>@<hostname> ~]$ ls \
> -al \
> ~

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Exercises

Info

Questions:

  1. Is there a difference between running ls versus ls -al?

  2. How can you find out what the –al options do?

  3. What does the pwd command do?

  4. From the command line, what happens if you press the up/down arrow keys?

...

Answers(1)

1: Is there a difference between running ls versus ls -al?

Expand
titleAnswer

Yes. The ls command is used to list files.

The characters after the '-' are flags, which select options associated with the command.

Code Block
[
arcc-t05@blog1
<username>@<hostname> ~]$ ls
Desktop  Documents  Downloads
[
arcc-t05@blog1
<username>@<hostname> ~]$ ls -al
total 76
drwxr-x---   8
arcc-t05 arcc-t05
<username> <username>  4096 Oct  3 13:57 .
drwxr-xr-x 925 root       root       32768 Sep 27 16:21 ..
-rw-------   1
arcc-t05 arcc-t05
<username> <username>   212 Sep 12 15:44 .bash_history
-rw-r--r--   1
arcc-t05 arcc-t05
<username> <username>    18 Aug 10 17:00 .bash_logout
-rw-r--r--   1
arcc-t05 arcc-t05
<username> <username>   141 Aug 10 17:00 .bash_profile
-rw-r--r--   1
arcc-t05 arcc-t05
<username> <username>   376 Aug 10 17:00 .bashrc
drwx------   3
arcc-t05 arcc-t05
<username> <username>  4096 Sep 12 11:36 .config
drwxr-xr-x   2
arcc-t05 arcc-t05
<username> <username>  4096 Aug 10 17:00 Desktop
drwxr-xr-x   2
arcc-t05 arcc-t05
<username> <username>  4096 Aug 10 17:00 Documents

...

Answers(2)

2: How can would you find out what the –al options do?

Expand
titleAnswer

  • Use man ls or ls --help

    • -a

...

    • is to specify “all”, which will include hidden files.

    • -l is to specify “long” which gives us the “long format” output about the listed files.

  • Options are also case sensitive:

    Code Block
    [

...

  • <username>@<hostname> ~]$ ls -A
.bash_history  .bash_profile  .config  Documents  .emacs     .kshrc    .mozilla  .zshrc
.bash_logout   .bashrc        Desktop  Downloads  .esd_auth  .lesshst  .ssh

...

Answers(3, 4)

3: What does the pwd command do?

Expand
titleAnswer

  • Use man pwd or pwd --help

  • pwd - print name of current/working directory

4: From the command line, what happens if you press the up/down arrow keys?

Expand
titleAnswer

Steps through the previous commands you’ve typed.

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What do you find?

This should access your previous commands. Hitting the up arrow once will give you the last command you typed in. Pressing it over again will produce the command that preceded that one, and so on.

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Previous

Getting Started with Linux

Workshop Home

Intro to Linux CLI: The File System

Next

The Linux File System

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