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Don't use ALL_CAPS variable names.

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ALL_CAPS variable names are traditionally "reserved" for use by the
shell/system.

(People often try to use PATH for things locally and then wonder why their
commands all stop working for example.
This commit is contained in:
Etan Reisner 2015-04-29 22:11:20 -04:00
parent 54b38b293f
commit 8b7a2fff9a
1 changed files with 29 additions and 29 deletions
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58
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@ -32,40 +32,40 @@ echo Hello world!
echo 'This is the first line'; echo 'This is the second line' echo 'This is the first line'; echo 'This is the second line'
# Declaring a variable looks like this: # Declaring a variable looks like this:
VARIABLE="Some string" Variable="Some string"
# But not like this: # But not like this:
VARIABLE = "Some string" Variable = "Some string"
# Bash will decide that VARIABLE is a command it must execute and give an error # Bash will decide that Variable is a command it must execute and give an error
# because it can't be found. # because it can't be found.
# Or like this: # Or like this:
VARIABLE= 'Some string' Variable= 'Some string'
# Bash will decide that 'Some string' is a command it must execute and give an # 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 # 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' # as a variable assignment valid only for the scope of the 'Some string'
# command.) # command.)
# Using the variable: # Using the variable:
echo $VARIABLE echo $Variable
echo "$VARIABLE" echo "$Variable"
echo '$VARIABLE' echo '$Variable'
# When you use the variable itself — assign it, export it, or else — you write # When you use the variable itself — assign it, export it, or else — you write
# its name without $. If you want to use variable's value, you should use $. # its name without $. If you want to use variable's value, you should use $.
# Note that ' (single quote) won't expand the variables! # Note that ' (single quote) won't expand the variables!
# String substitution in variables # String substitution in variables
echo ${VARIABLE/Some/A} echo ${Variable/Some/A}
# This will substitute the first occurance of "Some" with "A" # This will substitute the first occurance of "Some" with "A"
# Substring from a variable # Substring from a variable
LENGTH=7 Length=7
echo ${VARIABLE:0:LENGTH} echo ${Variable:0:Length}
# This will return only the first 7 characters of the value # This will return only the first 7 characters of the value
# Default value for variable # Default value for variable
echo ${FOO:-"DefaultValueIfFOOIsMissingOrEmpty"} echo ${Foo:-"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. # Note that it only returns default value and doesn't change variable value.
# Builtin variables: # Builtin variables:
@ -78,12 +78,12 @@ echo "Scripts arguments seperated in different variables: $1 $2..."
# Reading a value from input: # Reading a value from input:
echo "What's your name?" echo "What's your name?"
read NAME # Note that we didn't need to declare a new variable read Name # Note that we didn't need to declare a new variable
echo Hello, $NAME! echo Hello, $Name!
# We have the usual if structure: # We have the usual if structure:
# use 'man test' for more info about conditionals # use 'man test' for more info about conditionals
if [ $NAME -ne $USER ] if [ $Name -ne $USER ]
then then
echo "Your name isn't your username" echo "Your name isn't your username"
else else
@ -95,14 +95,14 @@ echo "Always executed" || echo "Only executed if first command fails"
echo "Always executed" && echo "Only executed if first command does NOT fail" echo "Always executed" && echo "Only executed if first command does NOT fail"
# To use && and || with if statements, you need multiple pairs of square brackets: # To use && and || with if statements, you need multiple pairs of square brackets:
if [ $NAME == "Steve" ] && [ $AGE -eq 15 ] if [ $Name == "Steve" ] && [ $Age -eq 15 ]
then then
echo "This will run if $NAME is Steve AND $AGE is 15." echo "This will run if $Name is Steve AND $Age is 15."
fi fi
if [ $NAME == "Daniya" ] || [ $NAME == "Zach" ] if [ $Name == "Daniya" ] || [ $Name == "Zach" ]
then then
echo "This will run if $NAME is Daniya OR Zach." echo "This will run if $Name is Daniya OR Zach."
fi fi
# Expressions are denoted with the following format: # Expressions are denoted with the following format:
@ -171,7 +171,7 @@ echo "There are $(ls | wc -l) items here."
echo "There are `ls | wc -l` items here." echo "There are `ls | wc -l` items here."
# Bash uses a case statement that works similarly to switch in Java and C++: # Bash uses a case statement that works similarly to switch in Java and C++:
case "$VARIABLE" in case "$Variable" in
#List patterns for the conditions you want to meet #List patterns for the conditions you want to meet
0) echo "There is a zero.";; 0) echo "There is a zero.";;
1) echo "There is a one.";; 1) echo "There is a one.";;
@ -179,10 +179,10 @@ case "$VARIABLE" in
esac esac
# for loops iterate for as many arguments given: # for loops iterate for as many arguments given:
# The contents of $VARIABLE is printed three times. # The contents of $Variable is printed three times.
for VARIABLE in {1..3} for Variable in {1..3}
do do
echo "$VARIABLE" echo "$Variable"
done done
# Or write it the "traditional for loop" way: # Or write it the "traditional for loop" way:
@ -193,16 +193,16 @@ done
# They can also be used to act on files.. # They can also be used to act on files..
# This will run the command 'cat' on file1 and file2 # This will run the command 'cat' on file1 and file2
for VARIABLE in file1 file2 for Variable in file1 file2
do do
cat "$VARIABLE" cat "$Variable"
done done
# ..or the output from a command # ..or the output from a command
# This will cat the output from ls. # This will cat the output from ls.
for OUTPUT in $(ls) for Output in $(ls)
do do
cat "$OUTPUT" cat "$Output"
done done
# while loop: # while loop:
@ -230,7 +230,7 @@ bar ()
} }
# Calling your function # Calling your function
foo "My name is" $NAME foo "My name is" $Name
# There are a lot of useful commands you should learn: # There are a lot of useful commands you should learn:
# prints last 10 lines of file.txt # prints last 10 lines of file.txt