control operators in linux

There is the list and description of control operators in linux.
Control operators play vital role in bash programming.
It will definitely help you to master the control operators in linux within an hour

& (ampersand)

It is one of the most useful control operators in linux.
When any command in the shell is ended with &,
the command starts to execute in the background
Therefore you'll not have to wait for command to finish.
You will get your shell back for another command
while the previous command is executing in background
For example:

• root@kali:~#   sleep   12   &
• Then the sleep operation will be executed in the background
• In b/w we can perform another linux command.
• It will also notify us when the command execution in background finishes

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; (semicolon)

It is among the most useful control operators in linux.
If we want to execute two or more commands on the single line,
then we have to use ; in b/w the commands.
the shell waiting for each command to finish before starting the next command.

For example
• echo   this is the tutorial on control operators in linux ; echo   it will teach about control operators in linux
• The output will be
• this is the tutorial on control operators in linux
  it will teach about control operators in linux

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$? (dollar question mark)

It is the shell parameter which stores the exit codes of
the previous command in the command shell.

For example
• cd  /Desktop
• echo  $?
• Output is   0
• cd   /Desktop
• echo  $?
• Output is  1

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&& (double ampersand)

&& is implemented by the shell as the logical AND.
It enables the execution of the second command
only if first command succeeds(i.e. it's exit code is 0)

for example
• echo linux is the best  &&  echo everyone knows that
• linux is the best
  everyone knows that
• mecho  linux is the best  &&  echo control operators in linux
• bash: mecho: command not found

---

|| (double vertical bar)

|| is implemented by the shell as the logical OR.
It enables the execution of the second command
only if first command fails(i.e. it's exit code is 1)

for example
• echo linux is the best  ||  echo everyone knows that
• linux is the best
• mecho  linux is the best  ||  echo control operators in linux
• bash:  mecho:  command  not  found
• everyone knows that

---

# (pound sign)

It is one of the most frequently used control operators in linux. It is used to write shell comments
Shell ignores everything written after the #
It doesn't play any role in command execution or shell expansion

• echo  control operators in linux  #it will print "control operators in linux" on the terminal
• output is: control operators in linux

---

\ (escaping special characters)

It enables the use of control characters,like  ;,/
but without the shell interpreting it,
this is called escaping characters.

for example
• echo this is linux  \;  it is very cool
• output: this is linux ; it is very cool
• echo control \"operators\" in \'linux\'
• output: control "operators" in 'linux'

---

End of the line backslash

It helps the line to extend upto the next line if it is ended with backslash
When it is found at the end of the line,
shell does not interpret the newline character and
waits on for execution of the command line until a newline without backslash is encountered.

For example
• root@kali:~#   echo control operators in linux\
  > plays important role\
  > in text presentation
  control operators in linuxplays important rolein text presentation