"English is a perplexing language. For example,
consider the words moon and good. To the uninitiated, the words
should rhyme, but the former is pronounced /mun/ (according to the
International Pronunciation Alphabet), while the latter is spoken
/good/. Seemingly, the only rule in English is exception.
"UNIX shells are equally perplexing. For instance, in the Bourne
shell (and most common UNIX shells), the phrases '$var', "$var",
and `$var` look alike but yield substantially different results.
(Each CLI in the shell examples presented in this article are
prefaced with the name of the active shell and the command
"In the sequence above, the variable var is set to the
two-letter string ls. In the initial echo command, the apostrophes
prevent interpretation of the variable, instead yielding a verbatim
copy of the quoted text, the four-letter string $var. Next, in
command 4, the double quotation marks do interpret the variable, so
the result is the string ls. Finally, the back quotes both
interpret the variable and run the intermediate result as a
subshell. Thus, `$var` yields the intermediate string ls, which
runs as a shell command to produce the contents of the local
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