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Download Unix Shell Programming is a tutorial aimed at helping Unix and
Transcript
$ i=1 $ i=$(expr $i + 1) Add 1 to i $ echo $i 2 $ In legacy shell programs, you're more likely to see expr used with back quotes: $ i=`expr $i + 1` Add 1 to i $ echo $i 3 $ Note that like the shell's built-in integer arithmetic, expr only evaluates integer arithmetic expressions. You can use awk or bc if you need to do floating point calculations. Also note that expr has other operators. One of the most frequently used ones is the : operator, which is used to match characters in the first operand against a regular expression given as the second operand. By default, it returns the number of characters matched. The expr command expr "$file" : ".*" returns the number of characters stored in the variable file, because the regular expression .* matches all the characters in the string. For more details on expr, consult your Unix User's Manual. Table A.5 in Appendix A summarizes the way quotes are handled by the shell.
