What is the meaning of the ${0##...} syntax with variable, braces and hash character in bash?
See the section on Substring removal in the Advanced Bash-Scripting Guide‡:
${string#substring}Deletes shortest match of
substringfrom front of$string.${string##substring}Deletes longest match of
substringfrom front of$string.
The substring may include a wildcard *, matching everything. The expression ${0##/*} prints the value of $0 unless it starts with a forward slash, in which case it prints nothing.
‡ The guide, as of 3/7/2019, mistakenly claims that the match is of $substring, as if substring was the name of a variable. It's not: substring is just a pattern.
Linux tip: Bash parameters and parameter expansions
${PARAMETER##WORD} Results in removal of the longest matching pattern from the beginning rather than the shortest.for example[ian@pinguino ~]$ x="a1 b1 c2 d2"[ian@pinguino ~]$ echo ${x#*1}b1 c2 d2[ian@pinguino ~]$ echo ${x##*1}c2 d2[ian@pinguino ~]$ echo ${x%1*}a1 b[ian@pinguino ~]$ echo ${x%%1*}a[ian@pinguino ~]$ echo ${x/1/3}a3 b1 c2 d2[ian@pinguino ~]$ echo ${x//1/3}a3 b3 c2 d2[ian@pinguino ~]$ echo ${x//?1/z3}z3 z3 c2 d2