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When to use dotglob for filename expansion in Bash?
If the shell option nocaseglob is enabled, the match is performed without regard to the case of alphabetic characters. When a pattern is used for filename expansion, the character ‘. ’ at the start of a filename or immediately following a slash must be matched explicitly, unless the shell option dotglob is set.
How to get filename and extension in Bash?
Using Bash, there’s also $ {file%.*} to get the filename without the extension and $ {file##*.} to get the extension alone. That is, file=”thisfile.txt” echo “filename: $ {file%.*}” echo “extension: $ {file##*.}”
What is the substitution for extension in Bash?
The command for EXTENSION substitutes a any number of characters followed by a “.” character at the start of the line, with nothing (i.e., it removes everything from the start of the line to the final dot, inclusive). This is a greedy substitution which is the default action.
What happens if there is no match for a filename in Bash?
If no matching filenames are found, and the shell option nullglob is disabled, the word is left unchanged. If the nullglob option is set, and no matches are found, the word is removed.
What is the name of the expansion variable in Bash?
Bash uses the value of the variable formed from the rest of parameter as the name of the variable $ {!variablename} This variable is then expanded and that value is used in the rest of the substitution, rather than the value of parameter itself. This is known as indirect expansion.
What does the$ character in shell expansion do?
The $ character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded can be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name.
How is an expansion performed in a shell?
After the command has been split into tokens (see Section 1.4.1.1 ), these tokens or words are expanded or resolved. There are eight kinds of expansion performed, which we will discuss in the next sections, in the order that they are expanded. After all expansions, quote removal is performed. 3.4.2. Brace expansion
What are the different types of expansion in Bash?
There are seven kinds of expansion performed: Expansion of expressions within braces. Expansion of the ~ character. How Bash expands variables to their values. Using the output of a command as an argument. How to use arithmetic in shell expansions. A way to write and read to and from a command.
Is the exclamation point subject to expansion in Bash?
The exceptions to this are the expansions of $ {! prefix *} and $ {! name [@]} described below. The exclamation point must immediately follow the left brace in order to introduce indirection. In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expansion.
What does it mean to expand a parameter in Bash?
Bash uses the value formed by expanding the rest of parameter as the new parameter; this is then expanded and that value is used in the rest of the expansion, rather than the expansion of the original parameter. This is known as indirect expansion.