Lab 2

ls -l /usr/bin > output.txt        # Save directory listing to file
echo "Hello" >> output.txt          # Add line to existing file
ls /nonexistent 2> error.txt        # Capture error message
command > out.txt 2> err.txt        # Separate output and errors
command &> all.txt                  # Everything to one file

ls -l | less                       # View long listing with paging
ps aux | grep firefox              # Find Firefox processes
cat file.txt | sort | uniq         # Display unique sorted lines
history | tail -20                 # Show last 20 commands
ls -l | wc -l                      # Count files in directory

nano filename                      # Open/create file in nano

gedit filename                     # Open GUI text editor

cat file                          # Display file contents
cat file1 file2                   # Display multiple files
cat file1 file2 > combined        # Combine files into one
cat > newfile                     # Create file from keyboard input (CTRL+D to end)

$ cat Ex1.txt
I am a student in the School of ICT.

sort file                         # Sort and display
sort file > output                # Sort and save
sort -r file                      # Reverse sort
sort -n file                      # Numerical sort

uniq file                         # Remove adjacent duplicates
uniq -c file                      # Count occurrences
uniq -d file                      # Show only duplicates
uniq -u file                      # Show only unique lines

$ sort file.txt | uniq            # Remove all duplicates
2
a
b
c
 
$ sort file.txt | uniq -c         # Count duplicates
   1 2
   1 a
   2 b
   2 c

wc file                           # Show lines, words, bytes
wc -l file                        # Lines only
wc -w file                        # Words only
wc -c file                        # Bytes only

$ wc Ex4.txt
6  6 12 Ex4.txt

ps                                # Show your processes
ps aux                            # Show ALL processes (detailed)
ps -ef                            # Alternative full listing
ps aux | grep process_name        # Find specific process

top                               # Real-time process monitor
htop                              # Enhanced version (if installed)

command                           # Runs in foreground (blocks terminal)

command &                         # Runs in background

sleep 100 &                       # Sleep for 100 seconds in background
[1] 12345                         # Output: [job#] PID

jobs                              # Show background/stopped jobs
jobs -l                           # Show with PIDs

fg                                # Resume most recent job in foreground
fg %1                             # Resume job [1] in foreground
fg %2                             # Resume job [2] in foreground

bg                                # Resume most recent stopped job in background
bg %1                             # Resume job [1] in background

$ nano file.txt                   # Start editing
[Press CTRL+Z]                    # Suspend nano
[1]+  Stopped                nano file.txt
$ ls                              # Do other work
$ fg                              # Return to nano

kill PID                          # Terminate process by PID
kill -9 PID                       # Force kill (SIGKILL)
kill %1                           # Kill job [1]

kill 8050                         # Terminate process with PID 8050
kill -9 8050                      # Force kill PID 8050
killall firefox                   # Kill all firefox processes

#!/bin/bash
# Comment: Description of script
 
# Your commands here
echo "Hello World"

chmod 755 script.sh               # Make executable
chmod +x script.sh                # Alternative method
./script.sh                       # Execute script

#!/bin/bash
echo "Script name: $0"
echo "First arg: $1"
echo "Second arg: $2"
echo "Total args: $#"

$ ./script.sh ABC 20
Script name: ./script.sh
First arg: ABC
Second arg: 20
Total args: 2

X=1                               # Number
Y="NetLab"                        # String
Name="John Doe"                   # String with spaces
Path=/home/student                # Path without quotes

X = 1                             # ERROR: spaces around =
Y= "NetLab"                       # ERROR: space after =
Z ="value"                        # ERROR: space before =

echo "Value of X is $X"
echo "Hello $Name"
Result=$X                         # Assign variable to another

#!/bin/bash
X=1
Y="NetLab"
echo "The value of X is $X."
echo "The value of Y is $Y."

if [ CONDITION ] ; then
    commands
else
    commands
fi

#!/bin/bash
St="Friday"
if [ "$St" = "Friday" ] ; then
    echo "It is Friday."
    echo "Let us have a party."
else
    echo "Not Friday."
fi

#!/bin/bash
Age=20
if [ $Age -gt 18 ] ; then
    echo "You are an adult."
else
    echo "You are a minor."
fi

#!/bin/bash
X=5
Y=3
if [ $X = $Y ] ; then    # WRONG! X and Y are numbers
    echo "Equal"
fi

if [ $X -eq $Y ] ; then  # CORRECT!
    echo "Equal"
fi

cat file1 file2 > combined.txt    # Combine files
sort file.txt > sorted.txt        # Sort file
sort file | uniq > unique.txt     # Remove duplicates
sort file | uniq -c > count.txt   # Count duplicates
ls -a > list.txt                  # List all files to file

ps aux | grep firefox             # Find Firefox process
kill 1234                         # Kill process 1234
command &                         # Run in background
jobs                              # List background jobs
fg %1                             # Bring job 1 to foreground

cat file | sort | uniq            # View unique lines
ls -l | wc -l                     # Count files
history | tail -20                # Last 20 commands
ps aux | grep process | wc -l     # Count matching processes
tail -f /var/log/syslog | grep error  # Monitor errors

>                                 # Redirect stdout (overwrite)
>>                                # Redirect stdout (append)
2>                                # Redirect stderr
&>                                # Redirect both stdout & stderr
|                                 # Pipe output to next command

cat file                          # Display file
sort file                         # Sort lines
uniq file                         # Remove adjacent duplicates
wc file                           # Count lines, words, bytes
grep pattern file                 # Search for pattern
head -n file                      # First n lines
tail -n file                      # Last n lines
tail -f file                      # Monitor file in real-time

ps aux                            # List all processes
kill PID                          # Terminate process
CTRL+C                            # Kill foreground process
CTRL+Z                            # Suspend foreground process
command &                         # Run in background
jobs                              # List jobs
fg %N                             # Foreground job N
bg %N                             # Background job N

#!/bin/bash                       # Shebang (first line)
$0, $1, $2, ...                   # Arguments
VarName=value                     # Assign variable (NO SPACES!)
$VarName                          # Use variable
chmod 755 script                  # Make executable
./script                          # Run script
 
# String comparison
[ "$var1" = "$var2" ]            # Equal
[ "$var1" != "$var2" ]           # Not equal
 
# Number comparison  
[ $num1 -eq $num2 ]              # Equal
[ $num1 -ne $num2 ]              # Not equal
[ $num1 -gt $num2 ]              # Greater than
[ $num1 -ge $num2 ]              # Greater or equal
[ $num1 -lt $num2 ]              # Less than
[ $num1 -le $num2 ]              # Less or equal