Homework & Coursework Questions

if command ; then

/some/command
if [ $? -eq 0 ] ; then

if /some/command ; then

if /usr/bin/test $a -eq $b ; then

if [ $a -eq $b ; then

if [ $a -eq $b ] ; then

if [$a -eq $b ] ; then
if[ $a -eq $b ] ; then
if [ $a -eq $b] ; then

(( x += 1 ))

let x=x+1

       ((expression))
              The expression is evaluated according to the rules described below under ARITHMETIC EVALUATION.  If the value of the expression is non-zero, the return status is 0;  otherwise  the
              return status is 1.  This is exactly equivalent to let "expression".

       [[ expression ]]
              Return a status of 0 or 1 depending on the evaluation of the conditional expression expression.  Expressions are composed of the primaries described below under CONDITIONAL EXPRES-
              SIONS.  Word splitting and pathname expansion are not performed on the words between the [[ and ]]; tilde expansion, parameter and variable expansion, arithmetic expansion, command
              substitution, process substitution, and quote removal are performed.  Conditional operators such as -f must be unquoted to be recognized as primaries.

              When used with [[, the < and > operators sort lexicographically using the current locale.

              When  the  ==  and != operators are used, the string to the right of the operator is considered a pattern and matched according to the rules described below under Pattern Matching.
              If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters.  The return value is 0 if the string matches  (==)  or  does
              not match (!=) the pattern, and 1 otherwise.  Any part of the pattern may be quoted to force it to be matched as a string.

              An  additional binary operator, =~, is available, with the same precedence as == and !=.  When it is used, the string to the right of the operator is considered an extended regular
              expression and matched accordingly (as in regex(3)).  The return value is 0 if the string matches the pattern, and 1 otherwise.  If the regular expression is  syntactically  incor-
              rect,  the conditional expression's return value is 2.  If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters.  Any
              part of the pattern may be quoted to force it to be matched as a string.  Substrings matched by parenthesized subexpressions within the regular expression are saved  in  the  array
              variable  BASH_REMATCH.   The element of BASH_REMATCH with index 0 is the portion of the string matching the entire regular expression.  The element of BASH_REMATCH with index n is
              the portion of the string matching the nth parenthesized subexpression.

              Expressions may be combined using the following operators, listed in decreasing order of precedence:

              ( expression )
                     Returns the value of expression.  This may be used to override the normal precedence of operators.
              ! expression
                     True if expression is false.
              expression1 && expression2
                     True if both expression1 and expression2 are true.
              expression1 || expression2
                     True if either expression1 or expression2 is true.

              The && and || operators do not evaluate expression2 if the value of expression1 is sufficient to determine the return value of the entire conditional expression.