🐧Linux Fundamentals

Find Files

• What is the name of the config file that has been created after 2020-03-03 and is smaller than 28k but larger than 25k?

find / -type f -name *.conf -newermt 2020-03-03 -size +25k -size -28k 2>/dev/null

• What is the name of the config file that has been created after 2020-03-03 and before 2020-03-05

find / -type f -name *.conf -newermt 2020-03-03 ! -newermt 2020-03-05 2>/dev/null

File Descriptors

A file descriptor (FD) in Unix/Linux operating systems is an indicator of connection maintained by the kernel to perform Input/Output (I/O) operations. In Windows-based operating systems, it is called filehandle. It is the connection (generally to a file) from the Operating system to perform I/O operations (Input/Output of Bytes). By default, the first three file descriptors in Linux are:

1. Data Stream for Input

   • STDIN – 0

2. Data Stream for Output

   • STDOUT – 1

3. Data Stream for Output that relates to an error occurring.

   • STDERR – 2

Example: 2>/dev/null This way, we redirect the resulting errors to the "null device," which discards all data. We can redirect the valid output to a file with 1>results.txt.

Find How Many logs files are on the system

#!/bin/bash
FILES=$(find / -type f -name *.log 2>/dev/null)
COUNTER=0
for f in $FILES
do
        echo $f
        let COUNTER++
done
echo $COUNTER

Find How Many packages are on the system

dpkg -l | grep -c '^ii'