An Introduction to Linux Shell Scripting: Glossary

A for loop repeats commands once for every thing in a list.

Every for loop needs a variable to refer to the thing it is currently operating on.

Use $name to expand a variable (i.e., get its value). ${name} can also be used.

Do not use spaces, quotes, or wildcard characters such as ‘*’ or ‘?’ in filenames, as it complicates variable expansion.

Give files consistent names that are easy to match with wildcard patterns to make it easy to select them for looping.

Use the up-arrow key to scroll up through previous commands to edit and repeat them.

Use Ctrl+R to search through the previously entered commands.

Use history to display recent commands, and !number to repeat a command by number.

Save commands in files (usually called shell scripts) for re-use.

bash filename runs the commands saved in a file.

$@ refers to all of a shell script’s command-line arguments.

$1, $2, etc., refer to the first command-line argument, the second command-line argument, etc.

Place variables in quotes if the values might have spaces in them.

Letting users decide what files to process is more flexible and more consistent with built-in Unix commands.

The basic conditional structure in Bash is built as: if…then…else…fi .

Bash has operators specific for string and integer comparisons.

Bash also has comparison operators useful to test the existance of files and directories.

Bash is an untyped language. This means that all variables are stored as strings.

The $(( )) construct is used to create arithmetic operations

Bash arrays are created byi enclosing the elements within a pair of brackets, ( )

We can find the size of a Bash array with the construct ${#ArrayName[@]}

Functions help us pack a set of operations with a single label.

Generally, Bash functions do not return values.

The output of Bash commands like cat, ls or find can be assigned to a Bash variable using the construct VAR=$(command)