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A type of redirection to feed a command list to an interactive program. Example: cat <<EOF Hello, World! EOF

Used to perform actions based on different conditions. Example: if [ $a -eq$b ]; then echo 'Equal'; fi

A numerical value returned by a command to indicate success or failure. Example: echo $? to display the exit status of the last command executed.$

Used for testing strings within conditional expressions. Example: if [ -z $STRING ]; then echo 'String is empty'; fi$

Allow for a multi-way branch based on value of a variable. Example: case $input in 1) echo 'One';; *) echo 'Other';; esac$

Evaluate arithmetic expressions inside a script. Example: echo $(( 2 + 2 )) outputs 4.$

Used for executing a block of commands repeatedly. Example: for i in {1..5}; do echo $i; done$

Allows the output of a command to replace the command itself. Example: CURRENT_DIR=$(pwd)$

Used for pattern matching in file names. Example: ls *.txt lists all txt files in a directory.

Used for testing properties of files and directories. Example: if [ -f $FILE ]; then echo 'File exists'; fi$

Creates a shortcut for a longer command. Example: alias ll='ls -l'

Used to send the output of one command as input to another. Example: ls | grep 'txt'

Access arguments passed to a bash script. Example: echo $1 to access the first argument.$

A way to store data that can be used and manipulated within the script. Example: MY_VARIABLE='Hello, World!'

Reusable blocks of code that can be called multiple times within a script. Example: greet() { echo 'Hello, 1'; }

Manage multiple jobs within a single Bash session. Example: Ctrl-Z to stop a job; fg to resume it.

Used to change the standard input/output/error streams. Example: echo 'Hello' > hello.txt

Expands variables and parameters to their values. Example: echo ${name:-'Anonymous'}$

Used to generate arbitrary strings. Example: echo {A,B,C}{1,2,3} generates A1 A2 A3 B1 B2 B3 C1 C2 C3.