# Implement a bash script that founds if a specific file is inside the directory listed in the current PATH environment variable.
# The name of the file is passed to the script as the first and only command line argument. When the file is found in 
# one or more directories listed in the PATH environment variable, the script must print the absolute path where the file is located.
#
# In practice, if the PATH environment variable is equal to /usr/sbin:/usr/bin:/sbin, the script must search a specific file_name
# in the directories: /usr/sbin, /usr/bin and /sbin.
#
# Example of execution of the script:
# $ ./ex5.sh ls
# /bin/ls



#!/bin/bash

if [ $# -ne 1 ] ; then
    echo Usage: $0 \<file_name\>; exit 1
fi


# A more complex control on the command line parameters (from a functional point of view it is equivalent to the previous check,
# i.e., it is only an example on how to use regular expressions inside an if)
# Double square braces are used to insert regular expressions in the if statement  [[   ]]
# The regular expression reported in the following recognize all the integer positive numbers with the exception of the number 1
# (the number starting with 0, for instance 0123, are not recognized)
if [[ $# =~ 0|[2-9]|[1-9][0-9]+ ]] ; then
    echo Usage: $0 \<nome_file\>; exit 1
fi


for i in $(echo $PATH | tr ':' ' ')
do
    if [ -e $i/$1 ] # if the path exists
    then
        if [ -f $i/$1 ] # if it is a file
        then echo $i/$1 
        fi
    fi
done