| Command | Description |
|---|---|
uname -a |
Display system information (kernel version, hostname, etc.) |
hostnamectl |
View and change hostname |
uptime |
Show how long the system has been running |
free -m |
Display memory usage in MB |
df -h |
Display disk space usage in human-readable format |
lsblk |
List information about block devices |
| Command | Description |
|---|---|
useradd <username> |
Create a new user |
passwd <username> |
Set or change a user's password |
usermod -aG <group> <username> |
Add a user to a group |
userdel <username> |
Delete a user |
groupadd <groupname> |
Create a new group |
groups <username> |
List groups for a user |
| Command | Description |
|---|---|
chmod <permissions> <file> |
Change file or directory permissions |
chown <user>:<group> <file> |
Change ownership of a file or directory |
chgrp <group> <file> |
Change group ownership of a file or directory |
umask |
Set default file permissions |
| Command | Description |
|---|---|
yum update |
Update all packages |
yum install <package> |
Install a package |
yum remove <package> |
Remove a package |
yum list installed |
List all installed packages |
yum search <package> |
Search for a package |
| Command | Description |
|---|---|
systemctl start <service> |
Start a service |
systemctl stop <service> |
Stop a service |
systemctl restart <service> |
Restart a service |
systemctl enable <service> |
Enable a service to start at boot |
systemctl disable <service> |
Disable a service from starting at boot |
systemctl status <service> |
Check the status of a service |
| Command | Description |
|---|---|
ip addr show |
Display IP address and network interfaces |
nmcli device status |
Show the status of network devices |
nmcli con up <connection-name> |
Bring up a network connection |
ping <host> |
Test network connectivity |
firewall-cmd --permanent --add-service=<service> |
Open a service in the firewall (e.g., HTTP, SSH) |
firewall-cmd --reload |
Reload the firewall to apply changes |
| Command | Description |
|---|---|
mount /dev/<device> /mnt |
Mount a device to a directory |
umount /mnt |
Unmount a device |
mkfs.ext4 /dev/<device> |
Format a device with ext4 filesystem |
ls -l |
List files in a directory with detailed information |
du -sh <directory> |
Show the size of a directory |
| Command | Description |
|---|---|
ps aux |
Display running processes |
top |
Interactive process viewer |
kill <PID> |
Terminate a process by PID |
killall <process_name> |
Terminate all processes with the given name |
| Command | Description |
|---|---|
crontab -e |
Edit the current user's crontab |
crontab -l |
List the current user's cron jobs |
systemctl restart crond |
Restart the cron service |
| Command | Description |
|---|---|
getenforce |
Check the current SELinux mode (Enforcing, Permissive, or Disabled) |
setenforce 0 |
Set SELinux to permissive mode temporarily |
semanage fcontext -a -t httpd_sys_content_t "/web(/.*)?" |
Set SELinux context for web directories |
restorecon -Rv /web |
Apply SELinux context to a directory recursively |
| Command | Description |
|---|---|
journalctl -xe |
View system logs and errors |
tail -f /var/log/messages |
Monitor the system log in real-time |
dmesg |
Display kernel ring buffer messages (hardware logs) |
| Command | Description |
|---|---|
passwd |
Change the current user's password |
visudo |
Edit the sudoers file |
firewall-cmd --list-all |
List all active firewall rules |
iptables -L |
List all iptables rules |
| Command | Description |
|---|---|
ssh user@hostname |
SSH into a remote server |
scp file user@hostname:/path/to/destination |
Securely copy a file to a remote server |
rsync -avz /src user@hostname:/dest |
Synchronize files between local and remote systems |
| Command | Description |
|---|---|
tar -czvf backup.tar.gz /path/to/directory |
Create a compressed backup of a directory |
tar -xzvf backup.tar.gz |
Extract a compressed backup |
rsync -av /source /destination |
Backup files using rsync |
| Command | Description |
|---|---|
useradd <username> |
Create a new user with the specified username. |
passwd <username> |
Set or change the password for the specified user. |
usermod -aG <group> <username> |
Add an existing user to a specified group. |
userdel <username> |
Delete the specified user. |
userdel -r <username> |
Delete the specified user and their home directory. |
id <username> |
Display the user ID (UID) and group ID (GID) information. |
whoami |
Display the username of the current user. |
lastlog |
Display the last login information for all users. |
| Command | Description |
|---|---|
groupadd <groupname> |
Create a new group with the specified name. |
groupdel <groupname> |
Delete the specified group. |
gpasswd -a <username> <group> |
Add a user to a group. |
gpasswd -d <username> <group> |
Remove a user from a group. |
groups <username> |
Display all groups the specified user belongs to. |
newgrp <group> |
Log in to a new group session. |
getent group <groupname> |
Display group information from the system databases. |
| Command | Description |
|---|---|
chmod <permissions> <file> |
Change the permissions of a file or directory. |
chown <user>:<group> <file> |
Change the owner and group of a file or directory. |
chgrp <group> <file> |
Change the group ownership of a file or directory. |
umask |
Display or set the default file creation permissions mask. |
ls -l |
List files and directories with their permissions. |
find / -user <username> |
Find all files and directories owned by a specified user. |
find / -group <groupname> |
Find all files and directories belonging to a specified group. |
| Command | Description |
|---|---|
visudo |
Edit the sudoers file to grant or revoke sudo privileges. |
sudo <command> |
Execute a command with elevated privileges. |
sudo -l |
List the allowed and forbidden commands for the current user. |
| File | Description |
|---|---|
/etc/passwd |
Contains user account information. |
/etc/shadow |
Contains encrypted passwords and account expiration data. |
/etc/group |
Contains group information. |
/etc/gshadow |
Contains group passwords (if any) and group administrator information. |
| Command | Description |
|---|---|
lsblk |
List all block devices, including partitions and LVM volumes. |
fdisk -l |
List partitions on all disks. |
fdisk /dev/sdX |
Create, modify, or delete partitions on /dev/sdX. |
parted /dev/sdX |
Advanced partition management, supporting GPT and MBR. |
mkfs.ext4 /dev/sdXn |
Create an ext4 filesystem on the partition /dev/sdXn. |
mkfs.xfs /dev/sdXn |
Create an XFS filesystem on the partition /dev/sdXn. |
blkid |
Display UUID and type information for block devices. |
df -h |
Display disk usage in human-readable format. |
mount /dev/sdXn /mnt |
Mount a partition to a directory. |
umount /mnt |
Unmount a partition from a directory. |
swapoff -a |
Disable all swap partitions. |
swapon /dev/sdXn |
Enable a swap partition on /dev/sdXn. |
| Command | Description |
|---|---|
pvcreate /dev/sdXn |
Initialize a physical volume on /dev/sdXn. |
vgcreate <vgname> /dev/sdXn |
Create a volume group with the specified name. |
lvcreate -L 10G -n <lvname> <vgname> |
Create a logical volume with the specified size and name. |
lvextend -L +5G /dev/<vgname>/<lvname> |
Extend a logical volume by 5 GB. |
resize2fs /dev/<vgname>/<lvname> |
Resize the filesystem on a logical volume after extending it. |
lvremove /dev/<vgname>/<lvname> |
Remove a logical volume. |
vgextend <vgname> /dev/sdXn |
Add a physical volume to an existing volume group. |
vgreduce <vgname> /dev/sdXn |
Remove a physical volume from a volume group. |
pvs, vgs, lvs |
Display information about physical volumes, volume groups, and logical volumes. |
| Command | Description |
|---|---|
mount -t <fstype> <device> <dir> |
Mount a filesystem of type <fstype> to a directory. |
umount <dir> |
Unmount the filesystem from the directory. |
tune2fs -l /dev/sdXn |
Display filesystem parameters for ext2/ext3/ext4 filesystems. |
xfs_info /mnt |
Display information about an XFS filesystem mounted at /mnt. |
fsck /dev/sdXn |
Check and repair a filesystem on /dev/sdXn. |
mkfs.ext4 /dev/sdXn |
Create an ext4 filesystem on /dev/sdXn. |
mkfs.xfs /dev/sdXn |
Create an XFS filesystem on /dev/sdXn. |
mount -o remount,rw /dev/sdXn /mnt |
Remount a filesystem as read-write. |
| Command | Description |
|---|---|
mkswap /dev/sdXn |
Create a swap area on /dev/sdXn. |
swapon /dev/sdXn |
Enable swap on the specified partition or file. |
swapoff /dev/sdXn |
Disable swap on the specified partition or file. |
free -m |
Display memory and swap usage in megabytes. |
swapon -s |
Display summary information about swap usage. |
| File | Description |
|---|---|
/etc/fstab |
File containing static information about filesystems to be mounted at boot. |
/dev/sda1 /mnt/data ext4 defaults 0 2- Disk and Partition Management: Commands for handling disk partitions, filesystems, and mounting.
- Logical Volume Management (LVM): Commands for creating, extending, and managing LVM volumes.
- Filesystem Management: Commands for working with filesystems, including mounting, creating, and checking.
- Swap Management: Commands for creating, enabling, and managing swap space.
- Auto-Mount Configuration: Guidance on configuring filesystems to be automatically mounted at boot via
/etc/fstab.
| Command | Description |
|---|---|
ip addr show |
Display IP addresses and network interfaces. |
nmcli device status |
Show the status of all network devices. |
ifconfig |
Display or configure network interfaces (deprecated, use ip). |
ip link set <interface> up/down |
Enable or disable a network interface. |
nmcli connection up <connection-name> |
Bring up a network connection by name. |
nmcli connection down <connection-name> |
Bring down a network connection by name. |
ethtool <interface> |
Display or change Ethernet device settings. |
nmtui |
Text-based user interface for network management. |
| Command | Description |
|---|---|
ip addr add <IP>/<netmask> dev <interface> |
Add an IP address to a network interface. |
ip addr del <IP>/<netmask> dev <interface> |
Remove an IP address from a network interface. |
nmcli con mod <connection> ipv4.addresses "<IP>/<netmask>" |
Modify the IP address for a connection. |
nmcli con mod <connection> ipv4.gateway "<gateway>" |
Set the default gateway for a connection. |
nmcli con mod <connection> ipv4.dns "<DNS1> <DNS2>" |
Set DNS servers for a connection. |
nmcli con reload |
Reload all network configurations. |
| Command | Description |
|---|---|
cat /etc/resolv.conf |
Display DNS server configuration. |
| `nmcli dev show | grep DNS` |
host <hostname> |
Resolve a hostname to an IP address. |
dig <domain> |
Query DNS information for a domain. |
nslookup <domain> |
Query DNS information (deprecated, use dig). |
| Command | Description |
|---|---|
ip route show |
Display the kernel routing table. |
ip route add <network> via <gateway> |
Add a new static route. |
ip route del <network> |
Delete a static route. |
route -n |
Display routing table with numeric IP addresses. |
nmcli con mod <connection> ipv4.routes "<network>/<CIDR> <gateway>" |
Add a persistent static route to a connection. |
| Command | Description |
|---|---|
firewall-cmd --state |
Check if the firewall is running. |
firewall-cmd --list-all |
List all active firewall rules. |
firewall-cmd --add-service=<service> |
Temporarily allow a service (e.g., HTTP, SSH). |
firewall-cmd --permanent --add-service=<service> |
Permanently allow a service. |
firewall-cmd --remove-service=<service> |
Temporarily remove a service. |
firewall-cmd --reload |
Reload firewall rules to apply changes. |
firewall-cmd --list-ports |
List all open ports in the firewall. |
firewall-cmd --add-port=<port>/tcp --permanent |
Open a specific port permanently (e.g., 8080/tcp). |
| Command | Description |
|---|---|
ping <host> |
Test network connectivity to a host. |
traceroute <host> |
Trace the route packets take to a host. |
mtr <host> |
Real-time network diagnostics tool combining ping and traceroute. |
netstat -tuln |
Display listening ports and their services. |
ss -tuln |
Display listening sockets (replacement for netstat). |
tcpdump -i <interface> |
Capture network packets on a specified interface. |
nmcli dev status |
Show the status of network devices. |
nmcli con show |
List all active and inactive network connections. |
| Command | Description |
|---|---|
systemctl start/stop/restart network |
Start, stop, or restart the network service. |
systemctl enable/disable network |
Enable or disable the network service at boot. |
systemctl status network |
Check the status of the network service. |
systemctl restart NetworkManager |
Restart the NetworkManager service. |
systemctl enable/disable NetworkManager |
Enable or disable NetworkManager at boot. |
systemctl status NetworkManager |
Check the status of the NetworkManager service. |
| Command | Description |
|---|---|
nmcli connection import type openvpn file <file.ovpn> |
Import an OpenVPN configuration file. |
nmcli connection up <vpn-connection> |
Connect to a VPN. |
nmcli connection down <vpn-connection> |
Disconnect from a VPN. |
nmcli con mod <vpn-connection> vpn.data "key=value" |
Modify VPN settings. |
ipsec status |
Check the status of IPsec VPN connections. |
| Command | Description |
|---|---|
nmcli con add type bond ifname bond0 mode active-backup |
Create a bond interface with active-backup mode. |
nmcli con add type bond-slave ifname eth0 master bond0 |
Add a slave interface to a bond. |
nmcli con mod bond0 ipv4.addresses "192.168.1.100/24" |
Assign an IP address to the bond interface. |
nmcli con up bond0 |
Bring up the bond interface. |
cat /proc/net/bonding/bond0 |
Display the status of the bond interface. |
| Command | Description |
|---|---|
timedatectl |
Display or set the system date and time. |
timedatectl set-ntp true |
Enable NTP synchronization. |
ntpdate <ntp-server> |
Synchronize the system clock with an NTP server. |
chronyc sources |
Display the current NTP sources. |
systemctl restart chronyd |
Restart the chrony service. |
systemctl enable chronyd |
Enable the chrony service at boot. |
| Command | Description |
|---|---|
systemctl start <service> |
Start a service. |
systemctl stop <service> |
Stop a service. |
systemctl restart <service> |
Restart a service. |
systemctl reload <service> |
Reload a service's configuration without stopping it. |
systemctl enable <service> |
Enable a service to start at boot. |
systemctl disable <service> |
Disable a service from starting at boot. |
systemctl status <service> |
Check the status of a service. |
systemctl is-active <service> |
Check if a service is currently active. |
systemctl is-enabled <service> |
Check if a service is enabled to start at boot. |
systemctl list-units --type=service |
List all active services. |
systemctl list-unit-files --type=service |
List all installed service unit files. |
| Command | Description |
|---|---|
systemctl daemon-reload |
Reload systemd manager configuration after a unit file change. |
systemctl cat <service> |
Display the content of a service's unit file. |
systemctl edit <service> |
Edit a service's unit file (opens in default editor). |
systemctl show <service> |
Show properties of a service unit. |
journalctl -u <service> |
View logs for a specific service. |
systemctl mask <service> |
Prevent a service from being started, manually or automatically. |
systemctl unmask <service> |
Unmask a service to allow it to start. |
systemctl link /path/to/custom.service |
Link a custom unit file into /etc/systemd/system/. |
| Command | Description |
|---|---|
journalctl -xe |
View the system journal (logs) with detailed errors and messages. |
journalctl -u <service> -b |
View logs for a service since the last boot. |
journalctl --since "YYYY-MM-DD HH:MM:SS" |
View logs since a specific date and time. |
journalctl --no-pager |
View the entire log without paging. |
systemctl --failed |
List all failed services and units. |
| Command | Description |
|---|---|
systemctl get-default |
Display the default target (runlevel). |
systemctl set-default <target> |
Set the default target (e.g., multi-user.target, graphical.target). |
systemctl isolate <target> |
Change to a specific target immediately (e.g., rescue.target). |
systemctl list-dependencies <target> |
List all dependencies of a target. |
systemctl rescue |
Switch to rescue mode (single-user mode with minimal services). |
systemctl emergency |
Switch to emergency mode (maintenance mode with only essential services). |
| Command | Description |
|---|---|
nano /etc/systemd/system/<name>.service |
Create or edit a custom service unit file. |
[Unit] |
Section of the unit file containing metadata and dependencies. |
[Service] |
Section of the unit file describing the service behavior. |
[Install] |
Section of the unit file containing installation information (e.g., wanted by target). |
systemctl daemon-reload |
Reload systemd configuration after creating/editing a unit file. |
systemctl start <name>.service |
Start the custom service. |
systemctl enable <name>.service |
Enable the custom service to start at boot. |
| Command | Description |
|---|---|
service <service> start |
Start a service using the SysVinit method. |
service <service> stop |
Stop a service using the SysVinit method. |
service <service> restart |
Restart a service using the SysVinit method. |
service <service> status |
Check the status of a service using the SysVinit method. |
chkconfig <service> on |
Enable a SysVinit service to start at boot. |
chkconfig <service> off |
Disable a SysVinit service from starting at boot. |
chkconfig --list <service> |
List the runlevels for a SysVinit service. |
/etc/init.d/<service> start |
Start a service directly from its init script. |
| Command | Description |
|---|---|
yum install qemu-kvm libvirt virt-install bridge-utils |
Install KVM and related packages. |
systemctl start libvirtd |
Start the libvirtd service. |
systemctl enable libvirtd |
Enable the libvirtd service to start at boot. |
virsh list --all |
List all virtual machines (VMs). |
virt-manager |
Launch the Virtual Machine Manager graphical interface. |
virt-install --name <vm_name> --memory <size> --vcpus <num> --disk <path>,size=<size> --cdrom <iso> |
Create and install a new VM. |
| Command | Description |
|---|---|
virsh start <vm_name> |
Start a virtual machine. |
virsh shutdown <vm_name> |
Shut down a virtual machine. |
virsh reboot <vm_name> |
Reboot a virtual machine. |
virsh destroy <vm_name> |
Forcefully stop a virtual machine. |
virsh suspend <vm_name> |
Suspend a virtual machine. |
virsh resume <vm_name> |
Resume a suspended virtual machine. |
virsh autostart <vm_name> |
Enable a VM to start automatically at host boot. |
virsh autostart --disable <vm_name> |
Disable a VM from starting automatically at host boot. |
virsh undefine <vm_name> |
Delete a VM definition. |
virsh console <vm_name> |
Access the console of a running VM. |
| Command | Description |
|---|---|
virsh pool-list |
List all storage pools. |
virsh pool-create <pool_xml> |
Create a new storage pool from an XML file. |
virsh pool-start <pool_name> |
Start a storage pool. |
virsh pool-destroy <pool_name> |
Destroy a storage pool (stop it without removing it). |
virsh pool-define-as <name> <type> --target <path> |
Define a new storage pool. |
virsh pool-delete <pool_name> |
Delete a storage pool (removes all storage volumes). |
virsh vol-list <pool_name> |
List all volumes in a storage pool. |
virsh vol-create-as <pool_name> <vol_name> <size> |
Create a new storage volume in a pool. |
virsh vol-delete <vol_name> --pool <pool_name> |
Delete a storage volume. |
virsh vol-info <vol_name> --pool <pool_name> |
Show detailed information about a storage volume. |
| Command | Description |
|---|---|
virsh net-list --all |
List all virtual networks. |
virsh net-create <network_xml> |
Create a new virtual network from an XML file. |
virsh net-start <network_name> |
Start a virtual network. |
virsh net-destroy <network_name> |
Destroy (stop) a virtual network. |
virsh net-autostart <network_name> |
Enable a virtual network to start automatically at host boot. |
virsh net-undefine <network_name> |
Delete a virtual network definition. |
virsh net-edit <network_name> |
Edit a virtual network configuration. |
virsh net-info <network_name> |
Display information about a virtual network. |
virsh iface-list |
List all physical network interfaces on the host. |
virsh iface-start <interface_name> |
Start a network interface. |
virsh iface-destroy <interface_name> |
Destroy (stop) a network interface. |
| Command | Description |
|---|---|
virsh snapshot-list <vm_name> |
List all snapshots for a VM. |
virsh snapshot-create-as <vm_name> <snapshot_name> |
Create a snapshot for a VM. |
virsh snapshot-revert <vm_name> <snapshot_name> |
Revert a VM to a specific snapshot. |
virsh snapshot-delete <vm_name> <snapshot_name> |
Delete a snapshot. |
virsh dumpxml <vm_name> > <path>.xml |
Backup a VM's configuration to an XML file. |
virsh define <path>.xml |
Restore a VM's configuration from an XML file. |
virsh vol-clone <source_vol> <dest_vol> --pool <pool_name> |
Clone a storage volume to create a backup. |
| Command | Description |
|---|---|
virsh setmem <vm_name> <size> --config |
Set the maximum memory allocation for a VM. |
virsh setvcpus <vm_name> <num> --config |
Set the number of virtual CPUs for a VM. |
virsh blkiotune <vm_name> --weight <weight> |
Set the block I/O weight for a VM. |
virsh schedinfo <vm_name> |
Display or set scheduling parameters for a VM. |
virsh setmaxmem <vm_name> <size> --config |
Set the maximum amount of memory that a VM can use. |
virsh vcpuinfo <vm_name> |
Display detailed information about the VCPUs of a VM. |
| Command | Description |
|---|---|
virt-clone --original <vm_name> --name <new_vm_name> --file <path> |
Clone an existing VM. |
virt-top |
Monitor virtual machine resources (similar to top command). |
virt-sysprep -d <vm_name> |
Prepare a VM for cloning by removing sensitive data. |
virt-resize --expand /dev/sda1 <source.img> <dest.img> |
Resize a VM disk image. |
virt-customize -a <disk.img> --run-command 'yum update -y' |
Customize a VM disk image. |
| Command | Description |
|---|---|
sudo apt-get update |
Update the package list from repositories. |
sudo apt-get upgrade |
Upgrade all installed packages to their latest versions. |
sudo apt-get dist-upgrade |
Upgrade packages, handling dependencies intelligently. |
sudo apt-get install <package> |
Install a package. |
sudo apt-get remove <package> |
Remove a package but keep its configuration files. |
sudo apt-get purge <package> |
Remove a package along with its configuration files. |
sudo apt-get autoremove |
Remove unnecessary packages that were automatically installed. |
sudo apt-get clean |
Clean up the local repository of retrieved package files. |
sudo apt-cache search <keyword> |
Search for a package by keyword. |
sudo apt-cache show <package> |
Display detailed information about a package. |
| Command | Description |
|---|---|
sudo add-apt-repository <repository> |
Add a new repository to the sources list. |
sudo apt-add-repository ppa:<repository> |
Add a Personal Package Archive (PPA) repository. |
sudo apt-get update |
Update the package list after adding a new repository. |
sudo apt-key add <keyfile> |
Add a repository’s GPG key from a file. |
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys <key> |
Add a repository’s GPG key using a keyserver. |
/etc/apt/sources.list |
Main configuration file for APT repositories. |
/etc/apt/sources.list.d/ |
Directory for additional repository list files. |
| Command | Description |
|---|---|
dpkg -l |
List all installed packages. |
dpkg -s <package> |
Display the status of a package (installed or not). |
dpkg -L <package> |
List the files installed by a package. |
dpkg -I <package.deb> |
Display information about a .deb package file. |
dpkg -i <package.deb> |
Install a package from a .deb file. |
dpkg -r <package> |
Remove a package but keep its configuration files. |
dpkg --purge <package> |
Remove a package along with its configuration files. |
dpkg-reconfigure <package> |
Reconfigure an already installed package. |
| Command | Description |
|---|---|
sudo apt-mark hold <package> |
Hold a package back from being upgraded. |
sudo apt-mark unhold <package> |
Remove a hold on a package to allow it to be upgraded. |
sudo apt-cache policy <package> |
Show installed and available versions of a package. |
sudo apt-get source <package> |
Download the source code of a package. |
sudo apt-get build-dep <package> |
Install build dependencies for a package. |
sudo apt-get check |
Check for broken dependencies. |
sudo apt-get -f install |
Fix broken dependencies by attempting to correct them. |
| Command | Description |
|---|---|
/etc/apt/preferences |
File for configuring package pinning (priority-based version selection). |
/etc/apt/preferences.d/ |
Directory for additional preferences files. |
Pin: release a=stable |
Example preference to pin a package to the stable release. |
Pin-Priority: 1001 |
Example pin priority to force installation of a specific version. |
| Command | Description |
|---|---|
/var/log/apt/history.log |
Log file for APT operations and history. |
/var/log/apt/term.log |
Log file for terminal output of APT commands. |
sudo apt-get -o Debug::pkgProblemResolver=yes dist-upgrade |
Debug package resolution problems during upgrade. |
sudo dpkg --configure -a |
Reconfigure any partially installed packages. |
sudo apt-get install -f |
Attempt to fix broken dependencies. |
| Concept | Description |
|---|---|
#!/bin/bash |
Shebang line to specify the script interpreter (Bash). |
chmod +x script.sh |
Make the script executable. |
./script.sh |
Run the script from the current directory. |
bash script.sh |
Execute the script using the Bash shell. |
sh script.sh |
Execute the script using the default shell. |
set -e |
Exit the script immediately if any command fails. |
set -x |
Print each command before executing it (useful for debugging). |
| Concept | Description |
|---|---|
VAR=value |
Define a variable. |
echo $VAR |
Access the value of a variable. |
VAR=$(command) |
Assign the output of a command to a variable. |
readonly VAR=value |
Declare a variable as read-only. |
unset VAR |
Unset or delete a variable. |
| Concept | Description |
|---|---|
read VAR |
Read input from the user into a variable. |
echo "Hello, World!" |
Print text to the terminal. |
echo -e "Line1\nLine2" |
Print text with newlines or special characters. |
echo -n "No newline" |
Print text without adding a newline at the end. |
cat file.txt |
Display the contents of a file. |
command > file.txt |
Redirect output of a command to a file, overwriting the file. |
command >> file.txt |
Append the output of a command to a file. |
| Concept | Description |
|---|---|
if [ condition ]; then ... fi |
Basic if statement. |
if [ condition ]; then ... else ... fi |
if-else statement. |
if [ condition1 ]; then ... elif [ condition2 ]; then ... fi |
if-elif-else statement. |
test condition |
Use test command to evaluate a condition. |
[[ condition ]] |
Advanced conditional expression. |
case $VAR in pattern1) commands ;; pattern2) commands ;; esac |
case statement for multiple conditions. |
| Concept | Description |
|---|---|
for VAR in list; do ... done |
Iterate over a list of values. |
while [ condition ]; do ... done |
Repeat a block of commands while a condition is true. |
until [ condition ]; do ... done |
Repeat a block of commands until a condition becomes true. |
break |
Exit a loop immediately. |
continue |
Skip the current iteration and proceed to the next one. |
| Concept | Description |
|---|---|
function name { commands; } |
Define a function. |
name |
Call a function. |
name arg1 arg2 |
Call a function with arguments. |
$1, $2, ... |
Access positional parameters within a function or script. |
return value |
Return a value from a function. |
| Concept | Description |
|---|---|
exit 0 |
Exit the script with a success status (0). |
exit 1 |
Exit the script with an error status (non-zero). |
trap 'commands' EXIT |
Execute commands on script exit. |
trap 'commands' ERR |
Execute commands when an error occurs. |
| `command |
| Concept | Description |
|---|---|
$0 |
The name of the script being executed. |
$1, $2, ... |
Positional parameters passed to the script. |
$@ |
All the arguments passed to the script. |
$# |
The number of arguments passed to the script. |
shift |
Shift positional parameters to the left. |
| Concept | Description |
|---|---|
touch filename |
Create an empty file or update its timestamp. |
rm filename |
Delete a file. |
cp source destination |
Copy a file or directory. |
mv source destination |
Move or rename a file or directory. |
find /path -name "pattern" |
Find files or directories by name. |
grep "pattern" file.txt |
Search for a pattern within a file. |
| Concept | Description |
|---|---|
bash -x script.sh |
Execute a script in debug mode (print each command). |
bash -n script.sh |
Check the script for syntax errors without executing it. |
time command |
Measure the time taken to execute a command. |
exec > logfile 2>&1 |
Redirect all script output to a file, including errors. |
set +x |
Disable debug mode in a script. |