susovanpanja/Escaping Special Characters

## Escaping Special Characters
The following characters have special meaning to the shell itself in some contexts and may need to be escaped in arguments:

` Backtick (U+0060 Grave Accent)
~ Tilde (U+007E)
! Exclamation mark (U+0021)
# Hash (U+0023 Number Sign)
$ Dollar sign (U+0024)
& Ampersand (U+0026)
* Asterisk (U+002A)
( Left Parenthesis (U+0028)
) Right parenthesis (U+0029)
 (⇥) Tab (U+0009)
{ Left brace (U+007B Left Curly Bracket)
[ Left square bracket (U+005B)
| Vertical bar (U+007C Vertical Line)
\ Backslash (U+005C Reverse Solidus)
; Semicolon (U+003B)
' Single quote / Apostrophe (U+0027)
" Double quote (U+0022)
↩ New line (U+000A)
< Less than (U+003C)
> Greater than (U+003E)
? Question mark (U+003F)
  Space (U+0020)1
Some of those characters are used for more things and in more places than the one I linked.

There are a few corner cases that are explicitly optional:

! can be disabled with set +H, which is the default in non-interactive shells.
{ can be disabled with set +B.
* and ? can be disabled with set -f or set -o noglob.
= Equals sign (U+003D) also needs to be escaped if set -k or set -o keyword is enabled.
Escaping a newline requires quoting — backslashes won't do the job. Any other characters listed in IFS will need similar handling. You don't need to escape ] or }, but you do need to escape ) because it's an operator.

Some of these characters have tighter limits on when they truly need escaping than others. For example, a#b is ok, but a #b is a comment, while > would need escaping in both contexts. It doesn't hurt to escape them all conservatively anyway, and it's easier than remembering the fine distinctions.

If your command name itself is a shell keyword (if, for, do) then you'll need to escape or quote it too. The only interesting one of those is in, because it's not obvious that it's always a keyword. You don't need to do that for keywords used in arguments, only when you've (foolishly!) named a command after one of them. Shell operators ((, &, etc) always need quoting wherever they are.
	The following characters have special meaning to the shell itself in some contexts and may need to be escaped in arguments:

	` Backtick (U+0060 Grave Accent)
	~ Tilde (U+007E)
	! Exclamation mark (U+0021)
	# Hash (U+0023 Number Sign)
	$ Dollar sign (U+0024)
	& Ampersand (U+0026)
	* Asterisk (U+002A)
	( Left Parenthesis (U+0028)
	) Right parenthesis (U+0029)
	(⇥) Tab (U+0009)
	{ Left brace (U+007B Left Curly Bracket)
	[ Left square bracket (U+005B)
	\| Vertical bar (U+007C Vertical Line)
	\ Backslash (U+005C Reverse Solidus)
	; Semicolon (U+003B)
	' Single quote / Apostrophe (U+0027)
	" Double quote (U+0022)
	↩ New line (U+000A)
	< Less than (U+003C)
	> Greater than (U+003E)
	? Question mark (U+003F)
	Space (U+0020)1
	Some of those characters are used for more things and in more places than the one I linked.

	There are a few corner cases that are explicitly optional:

	! can be disabled with set +H, which is the default in non-interactive shells.
	{ can be disabled with set +B.
	* and ? can be disabled with set -f or set -o noglob.
	= Equals sign (U+003D) also needs to be escaped if set -k or set -o keyword is enabled.
	Escaping a newline requires quoting — backslashes won't do the job. Any other characters listed in IFS will need similar handling. You don't need to escape ] or }, but you do need to escape ) because it's an operator.

	Some of these characters have tighter limits on when they truly need escaping than others. For example, a#b is ok, but a #b is a comment, while > would need escaping in both contexts. It doesn't hurt to escape them all conservatively anyway, and it's easier than remembering the fine distinctions.

	If your command name itself is a shell keyword (if, for, do) then you'll need to escape or quote it too. The only interesting one of those is in, because it's not obvious that it's always a keyword. You don't need to do that for keywords used in arguments, only when you've (foolishly!) named a command after one of them. Shell operators ((, &, etc) always need quoting wherever they are.