shell - Variable assignment in Unix -

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• command not found error in bash variable assignment 4 answers

when try following statements, doesn't assign values variables , loop goes infinite-

while ( [ $nos -ne 0 ] )     rem = `expr $nos % 10`     sum = `expr $sum + $rem`     nos = `expr $nos / 10` done 

but when remove spaces left , right side of assignment operator, works fine. -

while ( [ $nos -ne 0 ] )     rem=`expr $nos % 10`     sum=`expr $sum + $rem`     nos=`expr $nos / 10` done 

why shell behaviour that?

rem = `expr $nos % 10` 

runs command rem first argument =.

if weren't posix sh standard requiring assignments parse single word (which does), 1 couldn't pass = first argument command or function; hence, standard being written is.

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there's further expressive power based on whitespace in assignments well. instance:

rem= foo 

...runs foo environment variable rem set empty string duration of single command's execution, as

var=val foo 

sets var val while running foo. useful syntax; if var=val foo equivalent var="val foo", not possible.