Bash Scripting
String Matching
Regex
Use the new test (ie: x =~ regex ) to test regular expressions.
[[ zone36-ta =~ .*ta$ ]] && echo matched
Or use the new test with wildcards.
[[ zone36-ta =~ *ta ]] && echo matched
Useful Functions / Utilities
Here are some common functions I use in my scripts.
Prompt
You can prompt the user for an yes or no answer using this function. An optional default values are accepted as the second argument.
Example Usage:
if prompt "Is this okay?" Y ; then
echo "It's Okay!"
fi
if ! prompt "Is this okay?" N ; then
echo "It's not okay!"
fi
Source: <phorkie>https://phorkie.leo.home.steamr.com/13/embed</phorkie>
die
Similar to the {{code|die command in PHP which prints out a message before stopping execution.
Function:
function die {
echo $@
exit
}
Caveat when using in a subshell
This will not work inside a subshell as it will just quit the subshell rather than the script. To get around this, you may need to kill the parent PID instead.
Indent
Indents text piped to the function.
Source: <phorkie>https://phorkie.leo.home.steamr.com/14/embed</phorkie>
Usage:
echo "test" | Indent
test
echo "test" | Indent 2
test
Extracting / Parsing Filenames
Use the {{code|basename to extract filenames from a path and and {{code|dirname to extract the path of a filename.
Eg:
$ dirname /etc/hosts
/etc
$ basename /etc/hosts
hosts
To extract only the extension or the filename without the extension, use bash's string matching:
Filename=$(basename /etc/resolv.conf)
Ext="${Filename##*.}"
Name="${Filename%.*}"
Arithmetic Operations
Do integer arithmetic operations on variables within double brackets. For example:
Value=1
ValuePlusOne=$((Value + 1))
ValueTimes12=$((Value * 12))
The operators that are supported are:
+ - / * %
Bitwise operators also work:
^ (XOR) | (OR) & (AND)
Control Blocks
Switch
read -p "What do you want to do?: " Option
case "$Option" in
"K")
install_new_kernel
die "Complete!"
;;
"H")
usage
;;
*)
die "Stopping installation."
;;
esac
Snippets
Get First IP Address
ip a | /bin/grep inet | grep -v inet6 | tail -n+2 | head -n 1 | awk '{print $2}' | cut -d'/' -f1