Can a bash variable start with a number?
It can be a name, a number, or one of the special characters listed below. A variable is a parameter denoted by a name. and a name is defined as: name A word consisting solely of letters, numbers, and underscores, and beginning with a letter or underscore.
What does percentage mean in bash?
When the percent sign (%) is used in the pattern ${variable%substring}, it will return content of the variable with the shortest occurrence of substring deleted from the back of the variable. Manipulating Variables. Among many other handy functions, it explains what a double percent sign (%%) does, for example.
How to extract 5 digits from filename in Bash?
Given a filename in the form someletters_12345_moreleters.ext, I want to extract the 5 digits and put them into a variable. So to emphasize the point, I have a filename with x number of characters then a five digit sequence surrounded by a single underscore on either side then another set of x number of characters.
How to get the substring of a number in Bash?
The $ {numbers:0:1} parameter expansion in bash give you the substring of length 1 from the start of the string (offset zero). This is a bash -specific parameter substitution (also in some other shells, but not in the POSIX standard).
How to extract a part of a variable in Bash?
Both solutions presented are pure bash, with no process spawning involved, hence very fast. JB. JB. Generic solution where the number can be anywhere in the filename, using the first of such sequences: Another solution to extract exactly a part of a variable:
How to detect only digits in bash script?
If you want to detect only digits (not other character types) you should use a simple regular expression. In $var is a digit or it is empty (even not declared). Not the answer you’re looking for? Browse other questions tagged bash shell scripting or ask your own question.