Main Body

7 Quick Reference Guide

Common Notations

Here are some commonly used but easy-to-forget notations and syntax.

Notation Typical usage with mini-example Where to get more info
single quotes (‘) Creates literal string protecting special characters.
grep 'Al Shaji' namelist
Shell Variables
double quotes (“) Like single quotes but interprets $, \ for variables.
echo "Price: $value"
$(cmd) Command substitution.  Runs cmd and substitutes output of cmd at position of call.
man bash


set braces { } Formal variable specification; substrings.
echo ${alpha:3:5}

3 is offset (zero-based) and 5 is length

double parentheses (( )) Arithmetic expression.
a=$(( $a + 1 ))
man bash
left square bracket [ Synonym for test command.
if [ $op = MR ]

Closing right bracket is needed.

man test
[[ string =~ regex ]] Checks to see if regular expression (regex) is contained in string


[[ importing =~ port ]] will return TRUE

Can be used with variables, too.


[[ $title =~ $word ]] returns TRUE if $word is contained within $title

man bash
Character classes in regular expressions


Square brackets represent a single character pattern.  Thus,

r[aou]n matches ran, ron, or run.

[Pp]olish matches Polish or polish

man regex.7



Q1a: How do make my script executable?

Q1b: I’m getting an error message, “-bash: ./myscript: Permission denied”

A1: You need to issue the chmod command, either:

  • chmod 700 myscript
  • chmod u+x myscript



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Productivity in Common Operating Systems Copyright © 2022 by Lester Hiraki is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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