I am very new to Bash scripting, can someone explain to me how the $# and $? work in the following code?
#!/bin/bash
ARGS=3 # Script requires 3 arguments.
E_BADARGS=85 # Wrong number of arguments passed to script.
if [ $# -ne "$ARGS" ]
then
echo "Usage: `basename $0` old-pattern new-pattern filename"
exit $E_BADARGS
fi
old_pattern=$1
new_pattern=$2
if [ -f "$3" ]
then
file_name=$3
else
echo "File \"$3\" does not exist."
exit $E_BADARGS
fi
exit $?
From Learn Bash in Y minutes:
# Builtin variables:
# There are some useful builtin variables, like
echo "Last program's return value: $?"
echo "Script's PID: $$"
echo "Number of arguments passed to script: $#"
echo "All arguments passed to script: $@"
echo "The script's name: $0"
echo "Script's arguments separated into different variables: $1 $2..."
From https://www.gnu.org/software/bash/manual/html_node/Special-Parameters.html
$#
Expands to the number of positional parameters in decimal.
$?
Expands to the exit status of the most recently executed foreground pipeline.
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