Shebang is the '#!' in the beginning of the script.
It is used to choose the interpreter that the script will use.
If no shebang is specified, the current shell will be used.
#! /bin/bash
echo "This script is using the bash interpreter."To access variable's data use the $ operator.
The {} is optional.
#! /bin/bash
MY_VAR="Hello World"
echo $MY_VAR
echo ${MY_VAR}ddd # Note, this is example when to use {}By default, all variables are global.
The local key word can be used to make function variables local.
#! /bin/bash
MY_VAR="var"
if [ "$MY_VAR" = "var" ]
then
echo "This is true"
elif [ "$MY_VAR" = "Silly value" ]
then
echo "This will not be printed"
else
echo "This will not be printed"
fiThere are few test operators that bash provides.
For example, the -f checks if file exists.
#! /bin/bash
if [ -f $0 ]
then
echo "File $0 exists"
fi#! /bin/bash
FILES=$(ls .)
for FILE_NAME in ${FILES}
do
echo $FILE_NAME
doneEach command line param can be accessed with the $ operator:
#! /bin/bash
SCRIPT_COMMAND=$0
echo "This is \$0: $SCRIPT_COMMAND "
echo "This is \$1: $1"
echo "This is \$2: $2"The $@ variable contains list of all command line params (except for $0):
#! /bin/bash
for PARAM in $@
do
echo "This is param value: [ $PARAM ]"
done#! /bin/bash
echo "The exit code of previous command is $?"The following script check is host is reachable:
#! /bin/bash
HOST="google.com"
ping -c 1 $HOST
if [ "$?" -eq "0" ]
then
echo "$HOST reachable."
else
echo "$HOST unreachable."
fi
Note that return can be used to return value from function.
If no return is used, the return value is the return value of the
last command in the function.
#! /bin/bash
#Declare hello_world
function hello_world() {
echo "Hello World"
return 0
}
# Call hello_world
hello_world
Functions can access their parameters via $1, $2, etc.
Note that $0 is still the script name.
#! /bin/bash
function hello_world_with_params() {
echo "Hello World $1 $2 $3"
}
hello_world_with_params hi hey wow Local variables can be declared using the local keyword.
#! /bin/bash
function local_var_func() {
local MY_VAR="Hey there"
}
local_var_func* - Matches zero or more characters.
? - Matches exactly one character.
[] - Match one character from the characters in [].
[!] - Match any character that is not in [!].
[a-z] - Match character that is in the range of characters.
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