Expr: syntax error

The command in Bash allows you to evaluate expressions and return results. It can be extremely useful for performing math, comparisons, finding lengths and indexes, regex matching, and more.

In this comprehensive guide, we‘ll explore how to unleash the full power of expr in your Bash scripts.

How expr Works

The basic syntax of expr is:

Where can be any valid expression. expr will evaluate the expression and return the result.

Some examples:

As you can see, expr works well for math operations.

But we need to be careful with the syntax:

• Spaces are required around each operator
• Use a backslash before asterisks to escape them
• expr only works with integer math

Comparisons and Logical Operators

We can also use expr for comparisons and boolean logic:

The main operators and syntax rules are:

• Use , , , and for less than, greater than, equals, not equals
• Parentheses can group expressions
• performs a boolean AND
• performs a boolean OR

Again, remember that spaces and backslashes are required.

Comparing Strings

expr can also compare strings lexicographically:

This

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