Outline
Executing a Script
Making it Executable
To make a script file executable run the following command:
chmod u+x file.sh # makes it executable just for you
chmod a+x file.sh # makes it executable for everyone
comod a-x file.sh # remove permission to execut
Calling a script
If a script is in your path variable, you can just call it like a regular command. If a script is NOT in your path variable, you need to include the location when calling it.
./file.sh
# or
/home/documents/file.sh
Have a bin folder for your scripts
Make a bin folder where you keep all your scripts. This way you can have it in version control and it is easy to know where all your scripts are located. It also makes it easier to centrally locate all your scripts.
To add your bin folder to the path variable you can add the following in your .bash_profile file
export PATH=$PATH:/Users/mark.pearl/Source/personal/Settings_Bash/
Assume /Users/mark.pearl/Source/personal/Settings_Bash/ is where you script files are located.
Handling aliases
Another useful technique I have found is to store all your aliases in a script file. In your .bash_profile file you then do the following
source /Users/mark.pearl/Source/personal/Settings_Bash/general_aliases.sh
Assume /Users/mark.pearl/Source/personal/Settings_Bash/general_aliases.sh is where you script file containing your aliases is located.
Script Format
Start with a Shebang
The first line of a script file tells the OS what language the script file is based in. For bash shell scripts we want this to be a shebang (#!) with bash.
#!/bin/bash
Other OS like windows might have a different location for bash. Below is the most compatible shebang to use.
#!/usr/bin/env bash
Passing parameters to a script
Get positional parameters
$1, $2, $3 hold positional parameters
Use curly braces for double digits or more…
${10}, ${11}, …
Get name of script - $0
$0 holds the name of the script as it was called.
If you use symbolic links etc, it would have the original name that triggered the script.
Get all parameters passed in - $@
$@ is equivalent to $1, $2, $3, …, $n
Using double quotes around $@ keeps parameters with multiple words in them intact i.e. “$@”
Getting count of arguments - $#
$# holds the count of the arguments passed to the script
Shifting Positonal Parameters
Shift method shifts the positional parameters by one value.
$2 -> $1
$3 -> $2
$# lowered by 1
etc.
GetOpts
Utility to help parse argument lists
- Expects options to start with a dash (-a)
- Allows options that take an argument (-f fileName)
while getopts "b:s:r" opt; do
case $opt in
r) variable1="r set"
;;
b) variable1="b is now set"
;;
s) variable1="s is now set instead"
;;
\?)
exit 1 #exit with error 1
;;
esac
done
Variables in Scripts
Looping variables
for a in $@; do
echo $a;
done
String Manipulation
foo="foo bar qux"
bar=${foo/ /.} # sets one ' ' to . i.e. foo.bar qux
bar=${foo// /.} # sets all ' ' to . i.e. foo.bar.qux
Dates
Baisc
Get year-month-day from day
formattedDate=`date +%Y-%m-%d` # returns in format 2016-09-21
To see different formats go to the man page for date
Conditional branching
Basic if statement
if [ -e 'hasAValue' ]; then
echo "inside the then if"
exit
else
echo "inside the else block"
exit
fi
if [ "$variable" = "1" ]; then
echo "variable contains value 1"
else
if [ "$variable" = "2" ]; then
echo "variable contains value 2"
else
echo "variable contains some other value"
fi
fi
variable contains some other value
Base cas statement
case $variable in
1 ) echo "variable contains value 1"
;;
2 ) echo "variable contains value 2"
;;
* ) echo "variable contains some other value"
;;
esac
References
Why sh is not running automatically without putting sh in front
