diff options
Diffstat (limited to 'bash.html.markdown')
| -rw-r--r-- | bash.html.markdown | 208 |
1 files changed, 102 insertions, 106 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index c9a805ba..e0e4f88a 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -18,6 +18,7 @@ contributors: - ["Harry Mumford-Turner", "https://github.com/harrymt"] - ["Martin Nicholson", "https://github.com/mn113"] - ["Mark Grimwood", "https://github.com/MarkGrimwood"] + - ["Emily Grace Seville", "https://github.com/EmilySeville7cfg"] filename: LearnBash.sh translators: - ["Dimitri Kokkonis", "https://github.com/kokkonisd"] @@ -37,104 +38,107 @@ or executed directly in the shell. # As you already figured, comments start with #. Shebang is also a comment. # Simple hello world example: -echo Hello world! # => Hello world! +echo "Hello world!" # => Hello world! # Each command starts on a new line, or after a semicolon: -echo 'This is the first line'; echo 'This is the second line' -# => This is the first line -# => This is the second line +echo "This is the first command"; echo "This is the second command" +# => This is the first command +# => This is the second command # Declaring a variable looks like this: -Variable="Some string" +variable="Some string" # But not like this: -Variable = "Some string" # => returns error "Variable: command not found" -# Bash will decide that Variable is a command it must execute and give an error +variable = "Some string" # => returns error "variable: command not found" +# Bash will decide that `variable` is a command it must execute and give an error # because it can't be found. # Nor like this: -Variable= 'Some string' # => returns error: "Some string: command not found" -# Bash will decide that 'Some string' is a command it must execute and give an -# error because it can't be found. (In this case the 'Variable=' part is seen -# as a variable assignment valid only for the scope of the 'Some string' -# command.) +variable= "Some string" # => returns error: "Some string: command not found" +# Bash will decide that "Some string" is a command it must execute and give an +# error because it can't be found. In this case the "variable=" part is seen +# as a variable assignment valid only for the scope of the "Some string" +# command. # Using the variable: -echo $Variable # => Some string -echo "$Variable" # => Some string -echo '$Variable' # => $Variable -# When you use the variable itself — assign it, export it, or else — you write +echo "$variable" # => Some string +echo '$variable' # => $variable +# When you use a variable itself — assign it, export it, or else — you write # its name without $. If you want to use the variable's value, you should use $. # Note that ' (single quote) won't expand the variables! - -# Parameter expansion ${ }: -echo ${Variable} # => Some string -# This is a simple usage of parameter expansion -# Parameter Expansion gets a value from a variable. -# It "expands" or prints the value -# During the expansion time the value or parameter can be modified -# Below are other modifications that add onto this expansion - -# String substitution in variables -echo ${Variable/Some/A} # => A string -# This will substitute the first occurrence of "Some" with "A" - -# Substring from a variable -Length=7 -echo ${Variable:0:Length} # => Some st +# You can write variable without surrounding quotes but it's not recommended. + +# Parameter expansion ${...}: +echo "${variable}" # => Some string +# This is a simple usage of parameter expansion such as two examples above. +# Parameter expansion gets a value from a variable. +# It "expands" or prints the value. +# During the expansion time the value or parameter can be modified. +# Below are other modifications that add onto this expansion. + +# String substitution in variables: +echo "${variable/Some/A}" # => A string +# This will substitute the first occurrence of "Some" with "A". + +# Substring from a variable: +length=7 +echo "${variable:0:length}" # => Some st # This will return only the first 7 characters of the value -echo ${Variable: -5} # => tring -# This will return the last 5 characters (note the space before -5) +echo "${variable: -5}" # => tring +# This will return the last 5 characters (note the space before -5). +# The space before minus is mandatory here. -# String length -echo ${#Variable} # => 11 +# String length: +echo "${#variable}" # => 11 -# Indirect expansion -OtherVariable="Variable" -echo ${!OtherVariable} # => Some String -# This will expand the value of OtherVariable +# Indirect expansion: +other_variable="variable" +echo ${!other_variable} # => Some string +# This will expand the value of `other_variable`. -# Default value for variable -echo ${Foo:-"DefaultValueIfFooIsMissingOrEmpty"} +# The default value for variable: +echo "${foo:-"DefaultValueIfFooIsMissingOrEmpty"}" # => DefaultValueIfFooIsMissingOrEmpty -# This works for null (Foo=) and empty string (Foo=""); zero (Foo=0) returns 0. +# This works for null (foo=) and empty string (foo=""); zero (foo=0) returns 0. # Note that it only returns default value and doesn't change variable value. -# Declare an array with 6 elements -array0=(one two three four five six) -# Print first element -echo $array0 # => "one" -# Print first element -echo ${array0[0]} # => "one" -# Print all elements -echo ${array0[@]} # => "one two three four five six" -# Print number of elements -echo ${#array0[@]} # => "6" -# Print number of characters in third element -echo ${#array0[2]} # => "5" -# Print 2 elements starting from fourth -echo ${array0[@]:3:2} # => "four five" -# Print all elements. Each of them on new line. -for i in "${array0[@]}"; do - echo "$i" +# Declare an array with 6 elements: +array=(one two three four five six) +# Print the first element: +echo "${array[0]}" # => "one" +# Print all elements: +echo "${array[@]}" # => "one two three four five six" +# Print the number of elements: +echo "${#array[@]}" # => "6" +# Print the number of characters in third element +echo "${#array[2]}" # => "5" +# Print 2 elements starting from fourth: +echo "${array[@]:3:2}" # => "four five" +# Print all elements each of them on new line. +for item in "${array[@]}"; do + echo "$item" done -# Brace Expansion { } -# Used to generate arbitrary strings -echo {1..10} # => 1 2 3 4 5 6 7 8 9 10 -echo {a..z} # => a b c d e f g h i j k l m n o p q r s t u v w x y z -# This will output the range from the start value to the end value - # Built-in variables: -# There are some useful built-in variables, like +# There are some useful built-in variables, like: echo "Last program's return value: $?" echo "Script's PID: $$" echo "Number of arguments passed to script: $#" echo "All arguments passed to script: $@" echo "Script's arguments separated into different variables: $1 $2..." +# Brace Expansion {...} +# used to generate arbitrary strings: +echo {1..10} # => 1 2 3 4 5 6 7 8 9 10 +echo {a..z} # => a b c d e f g h i j k l m n o p q r s t u v w x y z +# This will output the range from the start value to the end value. +# Note that you can't use variables here: +from=1 +to=10 +echo {$from..$to} # => {$from..$to} + # Now that we know how to echo and use variables, -# let's learn some of the other basics of bash! +# let's learn some of the other basics of Bash! # Our current directory is available through the command `pwd`. # `pwd` stands for "print working directory". @@ -144,33 +148,46 @@ echo "I'm in $(pwd)" # execs `pwd` and interpolates output echo "I'm in $PWD" # interpolates the variable # If you get too much output in your terminal, or from a script, the command -# `clear` clears your screen +# `clear` clears your screen: clear -# Ctrl-L also works for clearing output +# Ctrl-L also works for clearing output. # Reading a value from input: echo "What's your name?" -read Name # Note that we didn't need to declare a new variable -echo Hello, $Name! +read name +# Note that we didn't need to declare a new variable. +echo "Hello, $name!" -# We have the usual if structure: -# use `man test` for more info about conditionals -if [ $Name != $USER ] -then +# We have the usual if structure. +# Condition is true if the value of $name is not equal to the current user's login username: +if [[ "$name" != "$USER" ]]; then echo "Your name isn't your username" else echo "Your name is your username" fi -# True if the value of $Name is not equal to the current user's login username -# NOTE: if $Name is empty, bash sees the above condition as: -if [ != $USER ] -# which is invalid syntax -# so the "safe" way to use potentially empty variables in bash is: -if [ "$Name" != $USER ] ... -# which, when $Name is empty, is seen by bash as: -if [ "" != $USER ] ... -# which works as expected +# To use && and || with if statements, you need multiple pairs of square brackets: +read age +if [[ "$name" == "Steve" ]] && [[ "$age" -eq 15 ]]; then + echo "This will run if $name is Steve AND $age is 15." +fi + +if [[ "$name" == "Daniya" ]] || [[ "$name" == "Zach" ]]; then + echo "This will run if $name is Daniya OR Zach." +fi +# There are other comparison operators for numbers listed below: +# -ne - not equal +# -lt - less than +# -gt - greater than +# -le - less than or equal to +# -ge - greater than or equal to + +# There is also the `=~` operator, which tests a string against the Regex pattern: +email=me@example.com +if [[ "$email" =~ [a-z]+@[a-z]{2,}\.(com|net|org) ]] +then + echo "Valid email!" +fi # There is also conditional execution echo "Always executed" || echo "Only executed if first command fails" @@ -193,27 +210,6 @@ bg kill %2 # %1, %2, etc. can be used for fg and bg as well -# To use && and || with if statements, you need multiple pairs of square brackets: -if [ "$Name" == "Steve" ] && [ "$Age" -eq 15 ] -then - echo "This will run if $Name is Steve AND $Age is 15." -fi - -if [ "$Name" == "Daniya" ] || [ "$Name" == "Zach" ] -then - echo "This will run if $Name is Daniya OR Zach." -fi - -# There is also the `=~` operator, which tests a string against a Regex pattern: -Email=me@example.com -if [[ "$Email" =~ [a-z]+@[a-z]{2,}\.(com|net|org) ]] -then - echo "Valid email!" -fi -# Note that =~ only works within double [[ ]] square brackets, -# which are subtly different from single [ ]. -# See https://www.gnu.org/software/bash/manual/bashref.html#Conditional-Constructs for more on this. - # Redefine command `ping` as alias to send only 5 packets alias ping='ping -c 5' # Escape the alias and use command with this name instead |