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Shell command, operator and separator/control characters:

Glamorous Grasshopper answered on February 19, 2022 Popularity 1/10 Helpfulness 1/10

answer Shell command, operator and separator/control characters:

Shell command, operator and separator/control characters:

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|  = pipe will take the first commands stdout as the second commands stdin.
|| = OR if first command is false, it will take the second.
|= = OR IS (mostly used in if statements)
&& = AND if first command is true, it will execute the second one.
!  = NOT (mostly used in if and test statements), but as a shell-command
     it opens a shell to run the command (ex. `! echo foo`)
!= = NOT IS (mostly used in if statements)
!$ = last commands last argument
!! = repeat last command
=  = IS (mostly used in if statements)
;  = will separate 2 commands as if they were written on separate command lines
;; = end of a case function in a case statement. (see 'case' further down)
$  = prefix to a variable like "$myvar"
$! = PID of the last child process.
$$ = PID of current process (PID == Process ID)
$0 = Shows program that owns the current process.
$1 = First argument supplied after the program/function on execution.
$2 = Second argument supplied after the program/function on execution. ($3 etc.)
$# = Shows the number of arguments.
$? = Any argument (good to use in 'if' statements)
$- = current option flags (I never ever had to use this one)
$_ = Last argument/Command
$* = All arguments
$@ = All arguments
#  = remmed line, anything on a line after "#" will be overlooked by the script
{  = start braces (starts a function)
}  = end braces   (ends a function)
[  = start bracket (multiple-argument specifiers)
]  = end bracket (multiple-argument specifiers)
@  = $@ is equivalent to "$1" "$2" etc. (all arguments)
*  = wild card (* can substitute any number of characters)
?  = wild card (? can substitute any single character)
"  = quote
'  = precise quote. (Will even include "'s in the quote)
`  = command quote. (variable=`ls -la` doing $variable will show the dir list)
.  = dot will read and execute commands from a file, ( . .bashrc )
&  = and. as suffix to executed file makes it go to the background(./program &)
0> = stdin stream director (I never seen this used in any script)
1> = stdout stream director (standard output)
2> = stderr stream director (standard error output)
%  = job character, %1 = fg job 1, %2 = fg job 2, etc.
>> = stream director append to a file
<< = stdin stream director. (cat > file << EOF ; anything ; EOF)
>  = stream director that will start at the top of the file
    (in if statements < and > may be used as greater-than
    and lesser-than, as: if [ "$1" >= "2" ])
\  = back-slash, takes away any special meaning with a character,
     \$var will not be treated as a variable.
     (and a new line will not be treated as a new line)
     Also a \ before a command, removes any alias on the command as: \rm
>& = stream director to stream director, ie. echo "a" 1>/dev/null 2>&1
     this directs 2> to the same place as 1>

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Source: subsignal.org

Tags: control-characters shell

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Contributed on Feb 19 2022

Glamorous Grasshopper

0 Answers Avg Quality 2/10

Shell command, operator and separator/control characters:

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