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| * It's easier to read. The character ` is difficult to read with small fonts or on large display. The key may to access the character may be located in a obscure place in non-US keyboard. | * It's easier to read. The character {{{`}}} is difficult to read with small or unusual fonts. * It's easier to type. The physical key to produce the character may be located in an obscure place on non-US keyboards. * The backtick is easily confused with a single quote. People who see {{{$()}}} don't normally press the wrong keys. On the other hand, some people who see {{{`cmd`}}} may mangle it into {{{'cmd'}}} because they don't know what a backtick is. |
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| * Newbies who see {{{$()}}} don't normally press the wrong keys. On the other hand, newbies who see {{{`cmd`}}} often mangle it into {{{'cmd'}}} because they don't know what a backtick is. |
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| echo "`echo \\a`" # prints a echo "`echo \\\a`" # prints \a echo "`echo \\\\a`" # prints \a}}} Inside {{{$()}}}, there are no such surprises. |
$ echo "`echo \\a`" "$(echo \\a)" a \a $ echo "`echo \\\\a`" "$(echo \\\\a)" \a \\a # Note that this is true for *single quotes* too! $ echo "`echo '\\'`" "$(echo '\\')" \ \\ }}} |
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| Backslashes are no more no less surprising than elsewhere IMHO {{{ echo `echo \a` # prints a echo `echo \\a` # prints a echo `echo \\\a` # prints \a echo `echo \\\\a` # prints \a echo $(echo \a) # prints a echo $(echo \\a) # prints \a echo $(echo \\\a) # prints \a echo $(echo \\\\a) # prints \\a }}} The same sort of things happens without any quotes or within "". I suspect the real advantage of $( ) here is that you don't need to take extra care of the quotes (\ ""), you just put them as usual, ie {{{echo "`echo \"foo bar\"`"}}} vs {{{echo "$( echo "foo bar")"}}} -- pgas ''Just for the record, \" inside {{{`backticks`}}} is only required in Korn shell and Bourne shell. Bash and dash both treat'' {{{ echo "`echo "foo bar"`"}}} ''exactly the same way they treat'' {{{ echo "$(echo "foo bar")"}}} ''although this is an excellent point that I'm going to add to the bullet list up above.'' -- GreyCat |
Why is $(...) preferred over `...` (backticks)?
For several reasons:
It's easier to read. The character ` is difficult to read with small or unusual fonts.
- It's easier to type. The physical key to produce the character may be located in an obscure place on non-US keyboards.
The backtick is easily confused with a single quote. People who see $() don't normally press the wrong keys. On the other hand, some people who see `cmd` may mangle it into 'cmd' because they don't know what a backtick is.
- It makes nesting command substitutions easier. Compare:
x=$(grep $(dirname "$path") file) x=`grep \`dirname "$path"\` file`
- Backslashes (\) inside backticks are handled in a non-obvious manner:
$ echo "`echo \\a`" "$(echo \\a)" a \a $ echo "`echo \\\\a`" "$(echo \\\\a)" \a \\a # Note that this is true for *single quotes* too! $ echo "`echo '\\'`" "$(echo '\\')" \ \\
Nested quoting inside $() is far more convenient.
echo "x is $(echo "$y" | sed ...)"
In this example, the quotes around $y are treated as a pair, because they are inside $(). This is confusing at first glance, because most C programmers would expect the quote before x and the quote before $y to be treated as a pair; but that isn't correct in shells. On the other hand,
echo "x is `echo \"$y\" | sed ...`"
The only time backticks are preferred is when writing code for the oldest Bourne shells, which do not know about $().