Bash Shell Scripting/Input-Output
The read built-in
editFrom help read
:
read: read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
Read a line from the standard input and split it into fields.
read is great for both user inputs and reading standard inputs/piping.
An example of user input:
# 'readline' prompt default variable name
read -e -p "Do this:" -i "destroy the ship" command
echo "$command"
Or even simpler:
pause() { read -n 1 -p "Press any key to continue..."; }
Hello-world level example of stdout operation:
echo 'Hello, world!' | { read hello
echo $hello }
Just be creative. For example, in many ways read can replace whiptail. Here is an example, extracted from Arthur200000's shell script:
# USAGE
# yes_or_no "title" "text" height width ["yes text"] ["no text"]
# INPUTS
# $LINE = (y/n) - If we should use line-based input style(read)
# $_DEFAULT = (optional) - The default value for read
yes_or_no() {
if [ "$LINE" == "y" ]; then
echo -e "\e[1m$1\e[0m"
echo '$2' | fold -w $4 -s
while read -e -n 1 -i "$_DEFAULT" -p "Y for ${5:-Yes}, N for ${6:-No}[Y/N]" _yesno; do
case $_yesno in
[yY]|1)
return 0
;;
[nN]|0)
return 1
;;
*)
echo -e "\e[1;31mINVALID INPUT\x21\e[0m"
esac
else whiptail --title "${1:-Huh?}" --yesno "${2:-Are you sure?}" ${3:-10} ${4:-80}\
--yes-button "${5:-Yes}" --no-button "$6{:-No}"; return $?
fi
}
# USAGE
# user_input var_name ["title"] ["prompt"] [height] [width]
# INPUTS
# $LINE = (y/n) - If we should use line-based input style(read)
# $_DEFAULT = (optional) - The default value for read; defaults to nothing.
user_input(){
if [ "$LINE" == "y" ]; then
echo -e "\e[1m${2:-Please Enter:}\e[0m" | fold -w ${4:-80} -s
read -e -i "${_DEFAULT}" -p "${3:->}" $1
else
eval "$1"=$(whiptail --title "$2" --inputbox "$3" 3>&1 1>&2 2>&3)
fi
}
Shell redirection
editIn shells, redirection is used for file I/O. The most common usage of is to redirect standard streams (stdin, stdout and stderr) to accept input from another program via piping, to save program output as a file, and to suppress program output by redirecting a stream to /dev/null
.