ksh: what does var=$(command) mean?

Shell Programming and Scripting
1

hi,

i can see in a script

it contains

var=$(
         myFile | grep -i err
)

why has this person done it like this? why not just

var=`myFile | grep -i err`

thanks

2

Well, '`' is small (hard to see/discern from "'"), vi '%' does not pair them, and it
does not nest. I am not sure if it swallows linefeeds -- probably. So, good style is to use ksh and $(). Also, use closed paren pairs in 'case' so they stay in balance for vi '%'.

1 Like
3

backtick `` means pass the result as a variable in old fashion
Using $() is new fashion (some shell implementation may not support this way to write things

1 Like
4

thanks guys

5

Yes, $() is not supported in bourne shell (sh).

6

Solaris' /bin/sh is one shell in a current OS that keeps popping up that does not support $() . But you can use /usr/xpg4/bin/sh instead ...

7

Note that, at least as far as ksh93 is concerned, there is a subtle difference between command substitution using $(...) and command substitution using `...`. In the second (obsolute) form, the string between the quotes is processed for special quoting characters before the command is substituted.

8

I totally agree backticks are terrible, but they do nest, you just have to escape them.

echo $( echo $( echo hallo ) )

echo ` echo \` echo hallo \` `
9

Multiple nesting is quickly getting insane with backquotes:

echo $(echo $(echo $(echo $(echo $(echo hallo)))))

vs

echo `echo \`echo \\\`echo \\\\\\\`echo \\\\\\\\\\\\\\\`echo hallo \\\\\\\\\\\\\\\` \\\\\\\` \\\` \` `
10

Reminds me of waterloo fred, an editor with buffers of commands but in buffers all command had to have doubled escapes, . . . That way madless lies.