Bash Glossary

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This is a list of all the Bash terms and commands explained in the Bash Tutorial. Click a term to see what it means, with an example.

Term	Description
Shell	A program that reads your commands and runs them
Terminal	The window where you type commands and see their output
Prompt	The text the shell shows when it is ready for a command
Command	An instruction you type at the prompt, like ls or mkdir
Argument	A value you give a command, like a file name
Option	A flag like -l or --lines that changes what a command does
Path	The location of a file or folder, with names joined by /
Absolute Path	A path that starts at the root folder /
Relative Path	A path read from the folder you are in, like docs or ../lib
Home Directory	Your own folder, written as ~ and stored in $HOME
Working Directory	The folder you are in right now, shown by pwd
Hidden File	A file whose name starts with a dot, shown only by ls -a
Wildcard	The * and ? characters that match many file names at once
File Permissions	Who may read, write or run a file, like rwxr-xr-x or 755
Executable	A file with the x permission, so you can run it as a command
Shebang	The #!/bin/bash line at the top that says which program runs a script
Script	A file of commands that Bash runs from top to bottom
Comment	A note that starts with # and that Bash ignores
Variable	A name that stores a value, set with name=value and read with $name
Environment Variable	A variable that is passed on to the programs the shell starts
PATH Variable	The list of folders where Bash looks for commands
export	Makes a variable available to programs started from the shell
Quoting	Double quotes expand $variables, single quotes keep text as it is
Escape Character	The backslash \ that makes the next character plain text
Command Substitution	$(command) puts the output of a command into a line or variable
Arithmetic Expansion	$(( )) does math with whole numbers, like $((x + 1))
Brace Expansion	{a,b,c} and {1..5} turn one word into many
Exit Status	The number a command returns when it ends: 0 means success
&& and \|\|	Run the next command only if the previous one succeeded (&&) or failed (\|\|)
Pipe	The \| symbol sends the output of one command into the next command
Redirection	Send output to a file, or read input from a file, with >, >> and <
stdin	Standard input: where a command reads its input from, normally the keyboard
stdout	Standard output: where a command writes its normal output, normally the screen
stderr	Standard error: a separate output stream for error messages
/dev/null	A special file that throws away everything written to it
Here Document	Give a command several lines of input, written right in the script
Here String	Give a command one string as input with <<<
if	Run commands only when a condition is true
test and [ ]	Check a condition, such as a number, a string or a file
[[ ]]	The Bash test with pattern matching, && and \|\| inside the brackets
case	Compare one value against several patterns and run the matching block
for Loop	Repeat commands once for each item in a list
while Loop	Repeat commands as long as a condition is true
until Loop	Repeat commands until a condition becomes true
break and continue	Leave a loop early (break) or skip to the next round (continue)
Function	A named block of commands you can run many times
Local Variable	A variable that only exists inside a function
Positional Parameters	$1, $2 and so on: the arguments given to a script or function
Special Parameters	Built-in variables like $#, $@, $? and $0
Array	A variable that holds a list of values, read by number
Associative Array	An array that uses names (keys) instead of numbers
read	Read a line of input into one or more variables
Alias	A short name you define for a longer command
source	Run a file's commands in the current shell, so its variables stay set
Background Job	A command that runs while you keep using the terminal
trap	Run commands when the script gets a signal or exits
cron	Run commands automatically on a schedule
Process	A running program, with its own process ID (PID)