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Today I noticed if I run:

ldd `which bash`

I get the expected output. But when I run

ldd 'which bash'

I get error ./which bash: No such file or directory.

So what is the difference between the two similar looking symbols?

OB7DEV
  • 201

1 Answers1

1

The ` is named a backquote, to evaluate a command.

The backquote is used in the old-style command substitution, e.g.

foo=`command`

The

foo=$(command)

syntax is recommended instead. Backslash handling inside $() is less surprising, and $() is easier to nest.

See http://mywiki.wooledge.org/BashFAQ/082

The single quote ' is used to prevent shell expansion from strings:

Learn how to quote properly in shell, it's very important :

"Double quote" every literal that contains spaces/metacharacters and every expansion: "$var", "$(command "$var")", "${array[@]}", "a & b". Use 'single quotes' for code or literal $'s: 'Costs $5 US', ssh host 'echo "$HOSTNAME"'. See
http://mywiki.wooledge.org/Quotes
http://mywiki.wooledge.org/Arguments
http://wiki.bash-hackers.org/syntax/words
when-is-double-quoting-necessary

Gilles Quénot
  • 33,867