unix exam 2

$VAR

Used to access the contents of a previously assigned name

VAR=value

Syntax for assigning information to a reusable name

$(command)

A method to run a command and return its result inside a script

`command`

An older syntax for inserting the output of a command

-e

Checks if something exists at a specified path

-f

Checks if something is a regular file

-d

Checks if something is a directory

-eq

Compares two numbers for equality

-ne

Checks if two numeric values are different

-gt

Used when comparing if one number is higher than another

-lt

Used when checking if one number is smaller than another

[ condition ]

Syntax used to evaluate a true or false expression

if [ condition ]; then ... fi

A way to control whether code runs based on a check

for var in list; do ... done

Used to repeat commands for each item in a group

while [ condition ]; do ... done

Repeats code as long as a test is true

echo

Displays text or values to the screen

read VAR

Takes input from the user and stores it in a named location

exit

Stops execution of the current script

fi

Indicates the conclusion of a decision structure

done

Marks the end of a repetition structure

#!/bin/bash

Placed at the top to specify which interpreter should run the file

Makefile

A script-like file that tells a build tool how to construct a program

make

A utility that reads instructions to build software components

Target (in Makefile)

The result that a build rule aims to produce

Dependency (in Makefile)

A required item that must be present or up-to-date to proceed

Rule (in Makefile)

A set of steps used to transform inputs into outputs during a build

gcc -c

Creates an intermediate compiled file but does not produce a runnable output

gcc -o

Used to define the name of the file that will be generated

Linking

Combines multiple compiled pieces into a single runnable program

Object File (.o)

An intermediate result from compiling code, not yet ready to run

Executable

The final product of the build process, capable of being launched directly

clean target

A command often used to remove generated files and reset the environment

-lm

Adds an extra resource commonly used for calculations during program building

Variables in Makefile

Custom placeholders used to simplify repetition in build scripts

gcc -Wall

Enables warnings to help spot possible mistakes in source code

getopts

Used to handle options provided when launching a script

trap

Allows a script to react to unexpected interruptions

exec

Replaces the current running task with a new one without returning

make clean

A quick way to delete everything produced during the build process

fork()

Creates a new process by duplicating the calling process

exec()

Replaces the current process image with a new program

wait()

Makes the parent process pause until a child finishes

waitpid()

Waits for a specific child process to finish

_exit()

Terminates a process immediately without flushing stdio buffers

getpid()

Returns the ID of the calling process

getppid()

Returns the ID of the parent process of the calling process

zombie process

A terminated child process that hasn't been waited on by the parent

orphan process

A child process whose parent has terminated

signal

A notification sent to a process to notify it of events like interrupts

kill()

Sends a signal to a process, often to terminate it

WIFEXITED

Macro that checks if a child terminated normally

WEXITSTATUS

Macro that retrieves the exit status of a terminated child

&

Runs a command in the background

fg

Resumes a background job in the foreground

bg

Resumes a stopped job in the background

jobs

Lists background and suspended jobs for the current shell

kill

Stops a process by sending it a signal

nice

Alters the priority of a process

nohup

Runs a command immune to hangups and logs output

ps

Displays currently running processes

top

Shows real-time system processes and resource usage

sleep

Pauses execution for a set time

%1

Refers to job number 1 in job control

%+

Refers to the current job

%-

Refers to the previous job