BASH - Revision history

Stooge: Cleaned up the article.

2024-08-10T06:15:40Z

Cleaned up the article.

← Older revision		Revision as of 06:15, 10 August 2024
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	Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple\|MAC OS X]]. It is a command line interfact as opposed to [[GUI\|graphical]], so that means retards like [[you]] don't use it. But if you're feeling frisky, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:\|:&};:", for even faster results!)		Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple\|MAC OS X]]. It is a command line interfact as opposed to [[GUI\|graphical]], so that means retards like [[you]] don't use it. But if you're feeling frisky, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:\|:&};:", for even faster results!)

	=Features=		==Features==
			===Auto completion===
	==Auto completion==

	Start typing and hit <tab> to make bash complete your input. If your input leads to ambiguous completions, you might have to hit <tab> a second time to see all recommendations.		Start typing and hit <tab> to make bash complete your input. If your input leads to ambiguous completions, you might have to hit <tab> a second time to see all recommendations.

	==Input/output forwarding/redirecting==		===Input/output forwarding/redirecting===

	Every input or output produced by a program invoked in the bash shell can be redirected to a file, another program or a different data stream.		Every input or output produced by a program invoked in the bash shell can be redirected to a file, another program or a different data stream.
Line 44:		Line 41:
	some_prog < some_file		some_prog < some_file

	==Variables==		===Variables===

	Variables are used to store pieces of information and associate them with a name to access them.		Variables are used to store pieces of information and associate them with a name to access them.
Line 68:		Line 65:
	${my_variable}		${my_variable}

	===Sub shells===		====Sub shells====
	Bash can also start subshells, that are other instances of bash that aere running inside the currently open bash to execute a set of commands. To execute some commands in a subshell, enclose them in brackets and put a dollar sign in front:		Bash can also start subshells, that are other instances of bash that aere running inside the currently open bash to execute a set of commands. To execute some commands in a subshell, enclose them in brackets and put a dollar sign in front:
	$( some fancy commands in a subshell )		$( some fancy commands in a subshell )
Line 77:		Line 74:
	$(( 101/0 )) # Dividing by zero works, too!? Oh shi--		$(( 101/0 )) # Dividing by zero works, too!? Oh shi--

	==Logical Expressions==		===Logical Expressions===
	Bash can evaluate logical expressions. In *NIX based systems, the two states of Boolean logic, True and False are represented by Numbers: 0 stands for True, any other number for False. There also exist two little helper applications which have no other purpose than providing True or Flase:		Bash can evaluate logical expressions. In *NIX based systems, the two states of Boolean logic, True and False are represented by Numbers: 0 stands for True, any other number for False. There also exist two little helper applications which have no other purpose than providing True or Flase:
	true		true
Line 83:		Line 80:
	They issue their value as return code (see next section)		They issue their value as return code (see next section)

	===Return codes===		====Return codes====
	Return codes are pieces of information returned by a program to the Operating System before it ends, usually a number. On *NIX based systems Programs use the definition of True and Flase as 0 and non-zero to indicate, if their run was successful. If they ran successfully, they return the number 0, if there was an error, any other number is returned. So we can use the return codes of programs for logical evaluation.		Return codes are pieces of information returned by a program to the Operating System before it ends, usually a number. On *NIX based systems Programs use the definition of True and Flase as 0 and non-zero to indicate, if their run was successful. If they ran successfully, they return the number 0, if there was an error, any other number is returned. So we can use the return codes of programs for logical evaluation.
	The return code of a program can be accessed by a variable (until the next program is run, which overwrites it with its own return code)		The return code of a program can be accessed by a variable (until the next program is run, which overwrites it with its own return code)
Line 94:		Line 91:
	return 9001		return 9001

	===Boolean operators===		====Boolean operators====
	====AND====		=====AND=====
	Returns True (0), if both the left hand and the right hand expression return True.		Returns True (0), if both the left hand and the right hand expression return True.
	expression1 && expression2		expression1 && expression2
	====OR====		=====OR=====
	Returns True, if either the left hand or the right hand expression return True.		Returns True, if either the left hand or the right hand expression return True.
	expression1 \|\| expression2		expression1 \|\| expression2
	====NOT====		=====NOT=====
	Inverts the value of the following expression.		Inverts the value of the following expression.
	! expression		! expression

	===Comparison===		====Comparison====
	Comparisons and tests can be done with the helper application 'test'. It for example provides the comparison operators '=', '!=', '>' and '<', but also much more like checking if a file exists, or is of a special type. To learn about the full capabilities of test, simply type		Comparisons and tests can be done with the helper application 'test'. It for example provides the comparison operators '=', '!=', '>' and '<', but also much more like checking if a file exists, or is of a special type. To learn about the full capabilities of test, simply type
	help test		help test
Line 113:		Line 110:
	[ 7 = 9001 ]		[ 7 = 9001 ]

	===Conditional statements===		====Conditional statements====
	To make use of all the logic we had above, we need to be able to make decisions based on them. That's what Bash's conditional statements (if, else) are for.		To make use of all the logic we had above, we need to be able to make decisions based on them. That's what Bash's conditional statements (if, else) are for.
	Since every good *NIX program makes use of return codes to indicate it's success, we can use every program as source of logic to make conditional statements.		Since every good *NIX program makes use of return codes to indicate it's success, we can use every program as source of logic to make conditional statements.
	====If====		=====If=====
	the if statement evaluates an expression and runs a series of commands, if the expression is true. Every ief/else statement is closed by the keyword 'fi' ('if' backwards)		the if statement evaluates an expression and runs a series of commands, if the expression is true. Every ief/else statement is closed by the keyword 'fi' ('if' backwards)
	if expression; then command1; command2; command_over9000; fi		if expression; then command1; command2; command_over9000; fi
Line 126:		Line 123:
	command_over9000		command_over9000
	fi		fi
	====Else====		=====Else=====
	To have an alternative set of commands executed, if the condition is false, Bash provides the else statement.		To have an alternative set of commands executed, if the condition is false, Bash provides the else statement.
	if expression; then some; commands; else some; other; commands; fi		if expression; then some; commands; else some; other; commands; fi
Line 139:		Line 136:
	commands		commands
	fi		fi
	====Else If====		=====Else If=====
	The else if statement is provided by the keyword 'elif'		The else if statement is provided by the keyword 'elif'
	if expression1; then some; commands; elif expression2; then some; other; commands; fi;		if expression1; then some; commands; elif expression2; then some; other; commands; fi;
Line 164:		Line 161:
	fi		fi

	==Line Endings==		===Line Endings===
	Usually a new line makes bash execute the typed line (except this line continues an unfinished statement)		Usually a new line makes bash execute the typed line (except this line continues an unfinished statement)

Line 187:		Line 184:
	(the white spaces are not strictly necessary, but make it a lot more readable)		(the white spaces are not strictly necessary, but make it a lot more readable)

	==Scripting==		===Scripting===
	Basically a script is nothing else than regular shell commands written to a file, so you don't have to type them over and over again.		Basically a script is nothing else than regular shell commands written to a file, so you don't have to type them over and over again.

	===Comments===		====Comments====
	Everything preceded by a '#' is a comment which is completely ignored by bash (You can still use '#' within strings, since the quotes discard it's special meaning). Comments can and should be used in scripts to explain complicated code with a not very obvious purpose. (You don't only do this for others, but also for yourself. Half a year after coding some piece of shit you'll be happy, if you commented properly)		Everything preceded by a '#' is a comment which is completely ignored by bash (You can still use '#' within strings, since the quotes discard it's special meaning). Comments can and should be used in scripts to explain complicated code with a not very obvious purpose. (You don't only do this for others, but also for yourself. Half a year after coding some piece of shit you'll be happy, if you commented properly)
	# This is a comment		# This is a comment

imported>Uberfukken at 01:12, 14 March 2019

2019-03-14T01:12:19Z

← Older revision		Revision as of 01:12, 14 March 2019
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	* [[wpcomment.sh]]		* [[wpcomment.sh]]

			{{softwarez}}
	{{programming}}		{{programming}}
	[[Category:Softwarez]]		[[Category:Softwarez]]

imported>Oddguy at 13:01, 23 March 2015

2015-03-23T13:01:55Z

← Older revision		Revision as of 13:01, 23 March 2015
(No difference)

imported>Oddguy at 13:01, 23 March 2015

2015-03-23T13:01:55Z

← Older revision		Revision as of 13:01, 23 March 2015
(No difference)

imported>Oddguy at 13:01, 23 March 2015

2015-03-23T13:01:55Z

← Older revision	Revision as of 13:01, 23 March 2015
(No difference)

imported>Oddguy at 13:01, 23 March 2015

2015-03-23T13:01:55Z

← Older revision		Revision as of 13:01, 23 March 2015
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	~~{{programming}}~~

	Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple\|MAC OS X]]. It is a command line interfact as opposed to [[GUI\|graphical]], so that means retards like [[you]] don't use it. But if you're feeling frisky, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:\|:&};:", for even faster results!)		Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple\|MAC OS X]]. It is a command line interfact as opposed to [[GUI\|graphical]], so that means retards like [[you]] don't use it. But if you're feeling frisky, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:\|:&};:", for even faster results!)
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	* [[wpcomment.sh]]		* [[wpcomment.sh]]

			{{programming}}
	[[Category:Softwarez]]		[[Category:Softwarez]]

imported>Gäwer at 05:16, 24 November 2011

2011-11-24T05:16:06Z

← Older revision		Revision as of 05:16, 24 November 2011
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	{{programming}}		{{programming}}

	Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple\|MAC OS X]]. It is a command line interfact as opposed to [[GUI\|graphical]], so that means retards like [[you]] don't use it. But if ~~your~~ feeling frisky, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:\|:&};:", for even faster results!)		Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple\|MAC OS X]]. It is a command line interfact as opposed to [[GUI\|graphical]], so that means retards like [[you]] don't use it. But if you're feeling frisky, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:\|:&};:", for even faster results!)

	=Features=		=Features=

imported>Gäwer: spelling

2011-11-24T05:15:41Z

spelling

← Older revision		Revision as of 05:15, 24 November 2011
Line 1:		Line 1:

	{{programming}}		{{programming}}

	Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple\|MAC OS X]]. It is a command line interfact as opposed to [[GUI\|graphical]], so that means retards like [[you]] don't use it. But if your feeling ~~firsky~~, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:\|:&};:", for even faster results!)		Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple\|MAC OS X]]. It is a command line interfact as opposed to [[GUI\|graphical]], so that means retards like [[you]] don't use it. But if your feeling frisky, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:\|:&};:", for even faster results!)

	=Features=		=Features=

imported>Unknown: Created page with " {{programming}} Bash is a shell that can be run on most UNIX derived systems, including Lunix and MAC OS X. It is a command line interfact as opposed to [..."

2011-04-16T10:58:09Z

Created page with " {{programming}} Bash is a shell that can be run on most UNIX derived systems, including Lunix and MAC OS X. It is a command line interfact as opposed to [..."

New page

{{programming}}

Bash is a [[shell]] that can be run on most [[UNIX]] derived systems, including [[Lunix]] and [[Apple|MAC OS X]]. It is a command line interfact as opposed to [[GUI|graphical]], so that means retards like [[you]] don't use it. But if your feeling firsky, enter this into your shell: "sudo rm -f /*". Do it. I DARE YOU! (Protip: Use ":(){:|:&};:", for even faster results!)

=Features=

==Auto completion==

Start typing and hit <tab> to make bash complete your input. If your input leads to ambiguous completions, you might have to hit <tab> a second time to see all recommendations.

==Input/output forwarding/redirecting==

Every input or output produced by a program invoked in the bash shell can be redirected to a file, another program or a different data stream.

'''''Pipes''''' are used to forward the output of one program to the input of another program.

Syntax:
prog1 | prog2

'''''Output redirecting''''' is used to redirect the output of a program to a file. It can be used in 2 different ways: Overwrite and append.

Syntax for overwriting:
some_prog > some_file

Syntax for appending:
some_prog >> some_file

The output of *NIX programs goes to two separated output streams: Standard output (stdout) and standard error (stderr). Therefor output redirecting also works for those separated streams. To make it easier to type, the streams are enumerated: Stdout is 1, Stderr is 2. The default way of output redirecting shown above redirects only stdout and could also be written
some_prog 1> some_file
or
some_prog 1>> some_file
To redirect the stderr stream to a file, use
some_prog 2> some_file
or
some_prog 2>> some_file
The two methods can be combined, this can be useful for error logging:
some_prog 1> output_file 2> error_logfile
To redirect both streams to one file, use
some_prog &> some_file

'''''Input redirecting''''' is used to redirect the content of a file to the input of a program. This enables you to process files with programs that usually only accept direct input.

Syntax:
some_prog < some_file

==Variables==

Variables are used to store pieces of information and associate them with a name to access them.

'''''Declaring variables''''' can be done in 2 different ways.

The simple way:
my_variable='my valuable piece of information'
Make sure that there is no space between the variable name and the equal sign. otherwise it won't work.

The elaborate way comes along with the Usage of the bash builtin command 'declare' which enables you to declare variables with specific attributes, for example to make them readonly. Use 'help declare' for further information.

'''''Reading the content of variables''''' is done by putting the dollar sign in front of the variable:
$my_variable

'''''To use a variable inside a string''''', you have to put the string in double quotes. In single quotes the special meaning of the dollar sign isn't interpreted by bash. The following examples will used the variable we declared above.
"My string contains $my_variable"
will result to 'My string contains my valuable piece of information', while
'My string contains $my_variable'
will result to 'My string contains $my_variable'

'''''To make sure the variable's content is recognzed as one piece''''' (Some programs you can pass your variables to, might get terrible hiccups if the content contains spaces and/or tabs), use curly brackets around the variable name (the whole thing still has to be preceded by the dollar sign):
${my_variable}

===Sub shells===
Bash can also start subshells, that are other instances of bash that aere running inside the currently open bash to execute a set of commands. To execute some commands in a subshell, enclose them in brackets and put a dollar sign in front:
$( some fancy commands in a subshell )
This is useful to assign the output of commands to a variable:
my_variable=$( some commands in a subshell produching some output )
In subshells bash can also do simple calculations, just enclose the term you want to claculate in two pairs of brackets and put a dollar sign in front:
$(( 9000+1 )) # It's over 9000!
$(( 101/0 )) # Dividing by zero works, too!? Oh shi--

==Logical Expressions==
Bash can evaluate logical expressions. In *NIX based systems, the two states of Boolean logic, True and False are represented by Numbers: 0 stands for True, any other number for False. There also exist two little helper applications which have no other purpose than providing True or Flase:
true
false
They issue their value as return code (see next section)

===Return codes===
Return codes are pieces of information returned by a program to the Operating System before it ends, usually a number. On *NIX based systems Programs use the definition of True and Flase as 0 and non-zero to indicate, if their run was successful. If they ran successfully, they return the number 0, if there was an error, any other number is returned. So we can use the return codes of programs for logical evaluation.
The return code of a program can be accessed by a variable (until the next program is run, which overwrites it with its own return code)
$?
To make use of return codes in a bash script, you can use the keyword 'return'. This also ends the current script.

Example for successful return:
return 0
Example for unsuccessful return:
return 9001

===Boolean operators===
====AND====
Returns True (0), if both the left hand and the right hand expression return True.
expression1 && expression2
====OR====
Returns True, if either the left hand or the right hand expression return True.
expression1 || expression2
====NOT====
Inverts the value of the following expression.
! expression

===Comparison===
Comparisons and tests can be done with the helper application 'test'. It for example provides the comparison operators '=', '!=', '>' and '<', but also much more like checking if a file exists, or is of a special type. To learn about the full capabilities of test, simply type
help test
Example for simple comparison:
test 7 = 9001
Test can be abbreviated by embedding the statement in square brackets (spaces between bracket and expression are necessary):
[ 7 = 9001 ]

===Conditional statements===
To make use of all the logic we had above, we need to be able to make decisions based on them. That's what Bash's conditional statements (if, else) are for.
Since every good *NIX program makes use of return codes to indicate it's success, we can use every program as source of logic to make conditional statements.
====If====
the if statement evaluates an expression and runs a series of commands, if the expression is true. Every ief/else statement is closed by the keyword 'fi' ('if' backwards)
if expression; then command1; command2; command_over9000; fi
if you don't like long lines, you can also type this like the following example (indenting not required, it's only to make the code more readable)
if expression
then
command1
command2
command_over9000
fi
====Else====
To have an alternative set of commands executed, if the condition is false, Bash provides the else statement.
if expression; then some; commands; else some; other; commands; fi
or in multiple lines:
if expression
then
some
commands
else
some
other
commands
fi
====Else If====
The else if statement is provided by the keyword 'elif'
if expression1; then some; commands; elif expression2; then some; other; commands; fi;
or better readable:
if expression1
then
some
commands
elif expression2
then
some
other
commands
fi
of course the elif statement can be followed by an else or another elif:
if expression1
then
command1
elif expression2
then
command2
else
command3
fi

==Line Endings==
Usually a new line makes bash execute the typed line (except this line continues an unfinished statement)

To avoid Bash execute at end of line, just put a backslash as last character in this line. Bash now will now consider the current and the following line as one long line:
some code that is very loooooooooooooong
equals to
some code that is \
very loooooooooooooong

You can also put multiple lines into one. Simply put a semicolon (';') at the place where ususually the new line would start:
some
code
that
could
also
fit
in
one
line
equals to
some; code; thet; could; also; fit; in; one; line
(the white spaces are not strictly necessary, but make it a lot more readable)

==Scripting==
Basically a script is nothing else than regular shell commands written to a file, so you don't have to type them over and over again.

===Comments===
Everything preceded by a '#' is a comment which is completely ignored by bash (You can still use '#' within strings, since the quotes discard it's special meaning). Comments can and should be used in scripts to explain complicated code with a not very obvious purpose. (You don't only do this for others, but also for yourself. Half a year after coding some piece of shit you'll be happy, if you commented properly)
# This is a comment
some_code # This is a comment, too
some_code '# this is not a comment' "# this neither." # "but this is one"
A very handy use of comments is to temporarily disable parts of code for testing/searching errors.
A special comment is the 'Shebang'. It is put into the first line of a script file to tell the operating system which program it should use to run the script. It consits of the '#' followed by an exclamation point and the path to the program that should be used to run the script. For bash scripts this would usually be
#!/bin/bash

==Examples==
The following examples might help you improve your bash skills. To try them, simply copy and paste them a bash shell, or paste them to a file, then make the file executable by running
chmod +x path/to/file
After that you can run the script by typing the path to it in the shell. To make it easier to call your awesome script, you can put it into a directory which is in bash's search path, then you can call your script by its filename only. (For user created scripts /usr/local/bin/ is a suitable place)

===THE GAME===
Always know if you just lost it, or if you're still in your 30 minutes period of immunity. Save to 'thegame', make executable and run every time you suspect you just lost THE GAME. Then the script will keep track of the last time you lost it to make sure you can enjoy all your 30 minutes of immunity.

<pre>
#!/bin/bash

CONFIG="${HOME}/.thegamerc" # Config file to store last time of losing

# Explicitly declare variables needed for time calculation as integers, to
# make sure they're not accidentally interpreted as strings
declare -i LAST_TIME_LOST
declare -i NOW=$(date +%s) # Now, a UNIX timestamp of the current time
declare -i TOLERANCE=1800 # Tolerance for not losing: 30 minutes

echo 'THE GAME.'

# Try to read last time of playing from config. Else default to 0 (UNIX time)
if [ -e ${CONFIG} ]
then
# Read only the first line of the config file,
# since there should be no more lines.
LAST_TIME_LOST=$(head -n 1 ${CONFIG})
else
LAST_TIME_LOST=0
fi

# PLAY!
if [ $((${LAST_TIME_LOST}+${TOLERANCE})) -lt ${NOW} ]
then
# If last time plus tolerance are before (lesser than) now, you lost.
echo 'You just lost it.'
# To make sure you can enjoy your 30 minutes of immunity,
# the timestamp of now is stored to the config file
echo ${NOW} > ${CONFIG}
else
DIFFERENCE=$(( ${LAST_TIME_LOST}+${TOLERANCE}-${NOW} ))
echo "Time remaining until you lose again: ${DIFFERENCE} seconds"
fi

# We are a polite game :P
echo 'Thank you for playing!'
</pre>

==See Also==

* [[Shell]]
* [[wpcomment.sh]]

[[Category:Softwarez]]