diff options
| -rw-r--r-- | bash.html.markdown | 70 |
1 files changed, 31 insertions, 39 deletions
diff --git a/bash.html.markdown b/bash.html.markdown index bccc5773..e0e4f88a 100644 --- a/bash.html.markdown +++ b/bash.html.markdown @@ -138,7 +138,7 @@ 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". @@ -148,33 +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" @@ -197,27 +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 |