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foo="/sdf/here/jfds" bar="${foo##*/}" Can anyone explain how the "${foo##*/}" expression works? I understand it will return the string after the last forward slash (i.e. jfds). However, I have no idea how it does or what this type of expression is called?
768
Simply put: \b allows you to perform a “whole words only” search using a regular expression in the form of \bword\b. A “word character” is a character that can be used to form words. All characters that are not “word characters” are “non-word characters”.
There is a method for matching specific characters using regular expressions, by defining them inside square brackets. For example, the pattern [abc] will only match a single a, b, or c letter and nothing else.
Each character in a regular expression (that is, each character in the string describing its pattern) is either a metacharacter, having a special meaning, or a regular character that has a literal meaning.
The caret ^ and dollar $ characters have special meaning in a regexp. They are called “anchors”. The caret ^ matches at the beginning of the text, and the dollar $ – at the end.
It is one of several shell features, generically called shell expansion. This particular expansion is called parameter expansion*.
You can think of this particular shell expansion form as a left-truncate string function. You must use the curly braces as shown (that is not optional)..
When you use only one #, it means left-truncate only the first occurrence of the pattern which follows (up to the closing }. When you use two ##, it means left-truncate all consecutive pattern-matches. The result of var="a/b/c"; echo ${var#*/} is b/c... echo ${var##*/} returns c.
There is a complementary right-truncate. It uses % instead of the #... (I "remember" which is which because # is like a bash comment; always on the left).
The * is treated as a bash wildcard expansion.
Here is a list of all shell expansions, presented in precedence order.
The order of expansions is:
1. brace expansion ... prefix{-,\,}postfix # prefix-postfix prefix,postfix .. {oct,hex,dec,bin} # oct hex dec bin . {a..b}{1..2} # a1 a2 b1 b2 . {1..04} # 01 02 03 04 . {01..4} # 01 02 03 04 . {1..9..2} # 1 3 5 7 9 . \$\'\\x{0..7}{{0..9},{A..F}}\' # $'\x00' .. $'\x7F' 2. tilde expansion .... ~ # $HOME ... ~axiom # $(dirname "$HOME")/axiom ... ~fred # $(dirname "$HOME")/fred .. ~+ # $PWD (current working directory) .. ~- # $OLDPWD (previous working directory. If OLDPWD is unset, ~- is not expanded. ie. It stays as-is, regardless of the state of nullglob.) # Expansion for Directories in Stack. ie. # The list printed by 'dirs' when invoked without options . ~+N # Nth directory in 'dirs' list (from LHS) . ~-N # Nth directory in 'dirs' list (from RHS) 3. parameter expansion .... ${VAR/b/-dd-} ... ${TEST_MODE:-0} .. ${str: -3:2} # note space after : . ${#string} 4. (processed left-to-right) variable expansion arithmetic expansion command substitution ▶5. word splitting # based on $IFS (Internal Field Seperator) ▷6. pathname expansion according to options such as: nullglob, GLOBIGNORE, ...and more # Note: =============== ▶ 5. word splitting ↰ ▷ 6. pathname expansion ↰ # ===================== ↳ are not performed on words between [[ and ]] If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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