Manage File from the Command Line

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File System Directories in RHEL9

.
├── afs
├── bin -> usr/bin
├── boot
├── dev
├── etc
├── home
├── lib -> usr/lib
├── lib64 -> usr/lib64
├── media
├── mnt
├── opt
├── proc
├── root
├── run
├── sbin -> usr/sbin
├── srv
├── sys
├── tmp
├── usr
└── var

Location	Purpose
/boot	Files required to start the boot process.
/dev	Special device files used to access hardware.
/etc	System-specific configuration files.
/home	User home directories for storing personal data and configurations.
/root	Home directory for the administrative superuser (root).
/run	Runtime data for processes started since the last boot (e.g., PID files, lock files). Recreated on reboot. Consolidates /var/run and /var/lock from earlier RHEL versions.
/tmp	Temporary files. Files not accessed or modified in 10 days are deleted automatically. The /var/tmp directory is another temporary space, with files deleted after 30 days.
/usr	Installed software, shared libraries, and read-only program data. Key subdirectories include:

• /usr/bin: User commands
• /usr/sbin: System administration commands
• /usr/local: Locally customized software | | /var | System-specific variable data (e.g., databases, cache directories, logs, spooled documents). Data persists between reboots. |

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Specifying File Paths

Absolute Path

• Begins at the root (/).

Relative Path

• .: Current directory
• ..: Parent directory

Navigation Commands

pwd          # Print working directory
ls           # List contents of a directory
ls -l        # Detailed list with permissions
ls -a        # Include hidden files
ls -la       # Combined detailed and hidden files view
cd           # Change directory
cd ~         # Go to the home directory
cd ..        # Go to the parent directory
touch        # Create an empty file

Managing Files and Directories

Command	Description
mkdir	Create directories.
mkdir -p	Create missing parent directories.
cp	Copy files.
cp -r	Copy directories and their contents.
mv	Move files and directories.
rm	Remove files.
rm -r	Remove directories and their contents.
rm -ri	Prompt user confirmation before removal (interactive mode).

Creating Links Between Files

Hard Links

ln {existing_file} {new_file}

• Hard links reference the same data store location as the original file.

• Check link count using ls -l.

• Remains functional even if the original file is deleted.

Limitations

• Can only link regular files (not directories or special files).

• Both files must be in the same file system (use df to check the file system).

Soft Links (Symbolic Links)

ln -s {existing_file_or_directory} {link_name}

• Can link any file or directory.

• Independent of the file system.

• Points to the file name rather than the data; becomes invalid if the original file is deleted and not recreated.

Matching File Names with Shell Expansions

Pattern Matching and Meta Characters

Pattern	Matches
*	Any string of zero or more characters.
?	Any single character.
[abc...]	Any character listed inside the brackets.
[!abc...]	Any character not listed inside the brackets.
[^abc]	Any character not listed inside the brackets.
[[:alpha:]]	Any alphabetic character.
[[:lower:]]	Any lowercase character.
[[:upper:]]	Any uppercase character.
[[:alnum:]]	Any alphanumeric character.
[[:punct:]]	Any printable character not a space or alphanumeric.
[[:digit:]]	Any digit (0-9).
[[:space:]]	Any whitespace (tabs, newlines, spaces).

Brace Expansion

• Expands sequences of strings.

echo {m..p} # Output: m n o p

Tilde Expansion

• Use ~ to represent the current user’s home directory.

Variable Expansion

VARIABLENAME=value

echo $VARIABLENAME

echo ${VARIABLENAME}

Command Substitution

• Replaces a command with its output.

$(command)

Protecting Arguments from Expansion

• Use \ to escape a single character.

• Use '' to prevent all expansions.

• Use "" to prevent all expansions except $, \, backtick , ! .