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Fix typos
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@ -4,20 +4,20 @@
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## Basic Commands
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### Elevated Priviledges and Users
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### Elevated Privileges and Users
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[sudo vs su](https://unix.stackexchange.com/questions/35338/su-vs-sudo-s-vs-sudo-i-vs-sudo-bash/35342)
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```bash
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sudo su # login as root (user must be sudoer, root password not required) DANGEROUS
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sudo -s # act as root and inherit current user enviroment (env as is now, along current dir and env vars) SAFE (can modify user enviroment)
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sudo -i # act as root and and use a clean enviroment (goes to user's home, runs .bashrc) SAFEST
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sudo su # login as root (user must be sudoers, root password not required) DANGEROUS
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sudo -s # act as root and inherit current user environment (env as is now, along current dir and env vars) SAFE (can modify user environment)
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sudo -i # act as root and and use a clean environment (goes to user's home, runs .bashrc) SAFEST
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sudo COMMAND # run a command w\ root permissions
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sudo -u USER COMMAND # run command as user
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su # become root (must know root password) DANGEROUS
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su - USER # change user and load it's home folder
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su USER # change user but dont load it's home folder
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su USER # change user but don't load it's home folder
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```
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### Getting Info
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@ -51,7 +51,7 @@ popd # return to previous directory (before pushd)
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```sh
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touch FILE # change FILE timestamp fi exists, create file otherwise
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cat [FILE] # concatenate files and print on statndard output (FD 1)
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cat [FILE] # concatenate files and print on standard output (FD 1)
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cat >> FILE # append following content ot file (Ctrl+D to stop)
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file FILE # discover file extension and format
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stat FILE # display file or file system status
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@ -60,7 +60,7 @@ tail # output the last part of a file
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tail [-nNUM] # output the last NUM lines
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more # filter for paging through text one screenful at a time
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less # opposite of more (display big file in pages), navigate with arrow keys or spacebar
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less # opposite of more (display big file in pages), navigate with arrow keys or space bar
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cut # remove sections from each line of files
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cut -[d --delimiter=DELIM] # use DELIM instead of TAB for field delimiter
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@ -74,10 +74,10 @@ rmdir DIRECTORY # remove directory only if is empty
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mkdir DIRECTORY # make directories
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mv SOURCE DESTINATION # move or raneme files
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mv SOURCE DESTINATION # move or rename files
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mv SOURCE DIRECTORY # move FILE to DIRECTORY
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cp SOURCE DESTINATION # copy SOURCE to DESTIANTION
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cp SOURCE DESTINATION # copy SOURCE to DESTINATION
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```
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### Files Permissions & Ownership
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@ -125,7 +125,7 @@ chgrp [OPTION]... GROUP FILE... # change group ownership
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find [path] [expression] # search file in directory hierarchy
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find [start-position] -type f -name FILENAME # search for a file named "filename"
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find [start-position] -type d -name DIRNAME # search for a directory named "dirname"
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find [path] -exec <command> {} \; # ececute command on found items (identified by {})
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find [path] -exec <command> {} \; # execute command on found items (identified by {})
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[ -f "path" ] # test if a file exists
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[ -d "path" ] # test if a folder exists
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@ -140,11 +140,11 @@ command | sudo tee FILE # operate on file w/o using shell as su
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echo # display a line of text
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echo "string" > FILE # write lin of text to file
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echo "string" >> FILE # append line o ftext to end of file (EOF)
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echo "string" >> FILE # append line of text to end of file (EOF)
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wget URL # download repositories to linux machine
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curl # dovnlaod the contents of a URL
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curl # download the contents of a URL
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curl [-I --head] # Fetch the headers only
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ps [-ax] # display processes
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@ -161,8 +161,8 @@ diff FILES # compare files line by line
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shellcheck FILE # shell linter
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xargs [COMMAND] # build and execute command lines from standard input
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# xargs reads items form the standard input, delimites by blanks or newlines, and executes the COMMAND one or more times with the items as argumests
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watch [OPTIONS] COMMAND # execute a program periodically, showing output fullscreen
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# xargs reads items form the standard input, delimited by blanks or newlines, and executes the COMMAND one or more times with the items as arguments
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watch [OPTIONS] COMMAND # execute a program periodically, showing output full-screen
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watch -n SECONDS COMMAND # execute command every SECONDS seconds (no less than 0.1 seconds)
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```
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@ -172,10 +172,10 @@ watch -n SECONDS COMMAND # execute command every SECONDS seconds (no less than
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```bash
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sed # stream editor for filtering and transforming text
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sed -E "s/REGEX/replacement/" # subsitute text ONCE (-E uses modern REGEX)
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sed -E "s/REGEX/replacement/g" # subsitute text multiple times (every match)
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sed -E "s/REGEX/replacement/" # substitute text ONCE (-E uses modern REGEX)
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sed -E "s/REGEX/replacement/g" # substitute text multiple times (every match)
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wc [FILE] # print newline, word and byte countd for each file
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wc [FILE] # print newline, word and byte count for each file
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wc [-m --chars] FILE # print character count
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wc [-c --bytes] FILE # print bytes count
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wc [-l --lines] FILE # print lines count
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@ -185,8 +185,8 @@ sort [FILE] # sort lines of a text file
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uniq [INPUT [OUTPUT]] # report or omit repeated lines (from INPUT to OUTPUT)
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uniq [-c --count] # prefix lines w/ number of occurrences
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uniq [-d --repeated] # plrint only duplicare lines, one for each group
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uniq [-D] # plrint only duplicare lines
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uniq [-d --repeated] # print only duplicare lines, one for each group
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uniq [-D] # print only duplicare lines
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paste [FILE] # merge lines of files
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paste [-d --delimiters=LIST] # use delimiters from LIST
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@ -10,7 +10,7 @@
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Interactive mode --> shell waits for user's commands
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Non-interactive mode --> shell runs scripts
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## File & Directories Permissons
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## File & Directories Permissions
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File:
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@ -35,12 +35,12 @@ Bash gets commands by reading lines.
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As soon as it's read enough lines to compose a complete command, bash begins running that command.
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Usually, commands are just a single line long. An interactive bash session reads lines from you at the prompt.
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Non-interactive bash processes read their commands from a file or stream.
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Files with a hashbang as their first line (and the executable permission) can be started by your system's kernel like any other program.
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Files with a shebang as their first line (and the executable permission) can be started by your system's kernel like any other program.
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### First Line Of Bash
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`#!/bin/env bash`
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Hashbang indicating whitch interpreter to use
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shebang indicating which interpreter to use
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### Simple Command
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@ -73,7 +73,7 @@ command_1 || command_2 || ... # execute successive commands only if preceding o
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{command_1; command_2; ...} # sequence of commands executed as one
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```
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### Functions (blocks of easely reusable code)
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### Functions (blocks of easily reusable code)
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`function_name () {compound_command}`
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Bash does not accept func arguments, parentheses must be empty
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@ -125,7 +125,7 @@ x>&-, x<&- # close FD x (stream disconnected from FD x)
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`*` matches any kind of text (even no text).
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`?` matches any single character.
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`[characters]` mathces any single character in the given set.
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`[characters]` matches any single character in the given set.
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`[[:classname:]]` specify class of characters to match.
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`{}` expand list of arguments (applies command to each one)
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@ -137,7 +137,7 @@ x>&-, x<&- # close FD x (stream disconnected from FD x)
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`@(pattern [| pattern ...])` matches when any of the patterns in the list appears just once. ("one of ...").
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`!(pattern [| pattern ...])` matches only when none of the patterns in the list appear. ("none of ...").
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## Command Substituition
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## Command Substitution
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With Command Substitution, we effectively write a command within a command, and we ask bash to expand the inner command into its output and use that output as argument data for the main command.
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@ -148,9 +148,9 @@ $(inner_command) # $ --> value-expansion prefix
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## Shell Variables
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```bash
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varname=value # variable assignement
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varname="$(command)" # command sobstituition, MUST be double-quoted
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"$varname", "${varname}" # variable expansion, MUST be double-quoted (name substituited w/ varaible content)
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varname=value # variable assignment
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varname="$(command)" # command substitution, MUST be double-quoted
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"$varname", "${varname}" # variable expansion, MUST be double-quoted (name substituted w/ variable content)
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$$ # pid
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$# # number of arguments passed
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@ -158,7 +158,7 @@ $@ # all arguments passed
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${n} # n-th argument passed to the command
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$0 # name of the script
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$_ # last argument passed to the command
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$? # error message of the last (previous) comman
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$? # error message of the last (previous) command
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!! # executes last command used (echo !! prints the last command)
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```
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@ -173,7 +173,7 @@ $? # error message of the last (previous) comman
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`${parameter/#pattern/replacement}` replaces the string that matches the pattern at the beginning of the value with the replacement.
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`${parameter/%pattern/replacement}` replaces the string that matches the pattern at the end of the value with the replacement.
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`${#parameter}` expands the length of the value (in bytes).
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`${parametr:start[:length]}` expands a part of the value, starting at start, length bytes long.
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`${parameter:start[:length]}` expands a part of the value, starting at start, length bytes long.
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Counts from the end rather than the beginning by using a (space followed by a) negative value.
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`${parameter[^|^^|,|,,][pattern]}` expands the transformed value, either upper-casing or lower-casing the first or all characters that match the pattern.
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Omit the pattern to match any character.
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@ -195,7 +195,7 @@ fi
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### Test Command
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`[[ arggument_1 <operator> argument_2 ]]`
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`[[ argument_1 <operator> argument_2 ]]`
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### Arithmetic expansion and evaluation
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@ -212,7 +212,7 @@ fi
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[[ "$a" -le "$b" ]] # less than or equal to
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```
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### Arithmetic Comperison Operators
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### Arithmetic Comparison Operators
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```bash
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(("$a" > "$b")) # greater than
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@ -221,10 +221,10 @@ fi
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(("$a" <= "$b")) # less than or equal to
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```
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### String Compatison Operators
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### String Comparison Operators
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```bash
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[ "$a" = "$b" ] # is equal to (whitespace atoun operator)
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[ "$a" = "$b" ] # is equal to (whitespace around operator)
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[[ $a == z* ]] # True if $a starts with an "z" (pattern matching)
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[[ $a == "z*" ]] # True if $a is equal to z* (literal matching)
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@ -244,7 +244,7 @@ fi
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```bash
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command_1 || command_2 # if command_1 fails executes command_2
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command_1 && command_2 # executes command_2 only if command_1 succedes
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command_1 && command_2 # executes command_2 only if command_1 succeeds
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```
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## Loops
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