Table of Contents
1.00 Introduction 1.01 Document Conventions 1.02 Copyright Notice 1.03 Feedback 2.00 Linux 3.00 Terminology 4.00 Directory Structure 5.00 Commands 5.01 Help Utilities 5.02 Files/Directories Utilities 5.03 Users and System Information Utilities 5.04a Permissions 5.04b Ownership, Permissions and Links Utilities 5.05 Hardware Utilities 5.06 Filter Utilities 5.07 Location Utilities 5.08 De&Compression Utilities 5.09 Jobs control Utilities 5.10 Networking Utilities 5.11 System & Admin and other Utilities 6.00 Symbols, Expansions 6.01 Key Combinations 6.02 Redirection Operators 6.03 Symbol Commands 6.04 File Descriptor 6.05 File Types (long list) 6.06 Wildcards 6.07 Common Regular Expressions 6.08 Extended Regular Expressions 7.00 Parameters and Variable, Attributes 7.01 Variable Commands 7.02 User Created Variables 7.03 Special Modifiers 7.04 Bash Keyword Variables 7.05 Positional Parameters 7.06 Escape Sequance 8.0 Vim 9.0 Scripts 10.00 Conclusion unnamed1
7.03 Special Modifiers #(especially used in scripts, look for more examples in section 8.00)
Symbol
Description
${variable:-word}
If the variable is set and is not empty, substitute its value. Otherwise substitute the value of word.
${variable:=word}
If the variable is set and is not empty, substitute its value. Otherwise set it to value of word. This is a permanent setting
${variable:+word}
If the variable is set and is not empty, substitute the value of word. Otherwise substitute nothing.
${variable:?word}
If the variable is set and is not empty, substitute the value of word. Otherwise print the value of word and exit the
Table of Contents
