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explain permission columns with tabs
 modified: docs/hpc/13_tutorial_intro_shell_hpc/06_scripts_variables_loops.mdx
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‎docs/hpc/13_tutorial_intro_shell_hpc/06_scripts_variables_loops.mdx

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import { Smile } from "lucide-react";
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import Tabs from '@theme/Tabs';
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import TabItem from '@theme/TabItem';
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# Scripts, variables, and loops
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That’s a huge amount of output: a full listing of everything in the directory. Let’s see if we can understand what each field of a given row represents, working from the left to right.
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### Column 1: File/Directory Permissions
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This column contains a block of subcolumns that define the permissions for a file or directory given in each row. The permissions are shown for three user types to perform three actions each.
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The user types are:
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- user (`u`): This refers to your permissions for this file/directory.
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- group (`g`): This refers to the permissions for people in the same group as this file/directory. You will see the group in the 4th column.
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- other (`o`): This refers to the permissions for all other users.
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The actions are:
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- read (`r`): This refers to the permission to read this file.
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- write (`w`): This refers to the permission to write to this file.
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- execute (`x`): This refers to the permission to execute this file.
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The following table show what each of the subcolumns refer to and their possible values:
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| directory | user read | user write | user execute | group read | group write | group execute | other read | other write | other execute |
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| ---------- | ---------- | ---------- | ------------ | ---------- | ----------- | ------------- | ---------- | ----------- | ------------- |
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| `d` or `-` | `r` or `-` | `w` or `-` | `x` or `-` | `r` or `-` | `w` or `-` | `x` or `-` | `r` or `-` | `w` or `-` | `x` or `-` |
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If there is a `-` in the directory column, the row refers to a file. If it contains a `d`, the row refers to a directory. The following columns behave in a similar manner. If they contain a `-`, the associated action is not allowed for the associated user type.
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### Column 2: References
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This counts the number of references (hard links) to the item (file, folder, symbolic link or “shortcut”).
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### Column 3: Owner
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This is the username of the user who owns the file.
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:::note
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Their permissions are indicated in the first permissions block of three after the directory column
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:::
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### Column 4: Group
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Each user has a primary group and is optionally a member of other groups. When a user creates a file, it is normally associated with the user’s primary group. At NYU HPC, all users are in a group named ‘users’, so group permission has little meaning.
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:::note
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Other members of this group have the permissions in the second block of three after the directory column
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:::
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### Column 5: Size of item
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This is the number of bytes in a file, or the number of filesystem blocks occupied by the contents of a folder.
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:::note
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We can use the `-h` option here to get a human-readable file size in megabytes, gigabytes, etc.
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:::
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### Column 6: Time last modified
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This is the last time the file was modified.
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### Column 7: Filename
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This is the name of the file/directory.
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::::info[What each column of the output above means:]
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<Tabs>
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<TabItem value="column1" label="File/Directory Permissions">
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This column contains a block of subcolumns that define the permissions for a file or directory given in each row. The permissions are shown for three user types to perform three actions each.
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The user types are:
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- user (`u`): This refers to your permissions for this file/directory.
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- group (`g`): This refers to the permissions for people in the same group as this file/directory. You will see the group in the 4th column.
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- other (`o`): This refers to the permissions for all other users.
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The actions are:
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- read (`r`): This refers to the permission to read this file.
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- write (`w`): This refers to the permission to write to this file.
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- execute (`x`): This refers to the permission to execute this file.
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The following table show what each of the subcolumns refer to and their possible values:
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| directory | user read | user write | user execute | group read | group write | group execute | other read | other write | other execute |
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| ---------- | ---------- | ---------- | ------------ | ---------- | ----------- | ------------- | ---------- | ----------- | ------------- |
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| `d` or `-` | `r` or `-` | `w` or `-` | `x` or `-` | `r` or `-` | `w` or `-` | `x` or `-` | `r` or `-` | `w` or `-` | `x` or `-` |
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If there is a `-` in the directory column, the row refers to a file. If it contains a `d`, the row refers to a directory. The following columns behave in a similar manner. If they contain a `-`, the associated action is not allowed for the associated user type.
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</TabItem>
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<TabItem value="column2" label="References">
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This counts the number of references (hard links) to the item (file, folder, symbolic link or “shortcut”).
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</TabItem>
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<TabItem value="column3" label="Owner">
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This is the username of the user who owns the file.
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:::tip
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Their permissions are indicated in the first permissions block of three after the directory column
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:::
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</TabItem>
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<TabItem value="column4" label="Group">
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Each user has a primary group and is optionally a member of other groups. When a user creates a file, it is normally associated with the user’s primary group. At NYU HPC, all users are in a group named ‘users’, so group permission has little meaning.
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::: tip
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Other members of this group have the permissions in the second block of three after the directory column
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:::
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</TabItem>
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<TabItem value="column5" label="Size of item">
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This is the number of bytes in a file, or the number of filesystem blocks occupied by the contents of a folder.
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We can use the `-h` option here to get a human-readable file size in megabytes, gigabytes, etc.
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</TabItem>
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<TabItem value="column6" label="Time last modified">
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This is the last time the file was modified.
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</TabItem>
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<TabItem value="column7" label="Filename">
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This is the name of the file/directory.
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</TabItem>
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</Tabs>
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::::
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## Changing Permissions
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As previously mentioned, in Unix a file has three basic permissions, each of which can be set for three types of user. Those three permission also have a numeric value:
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:::tip[Key Points]
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- A shell script is just a list of bash commands in a text file.
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- To make a shell script file executable, run `chmod +x script.sh`.
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:::
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:::

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