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Update bash help:

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- refresh read command sample
- fix if examples and && with ||
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EmilySeville7cfg 2022-08-19 11:09:16 +10:00
parent 7bcf933601
commit 42040d6d7d
1 changed files with 31 additions and 39 deletions
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70
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@ -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