Validating user input in shell script
If the match fails, the `:' operator returns the null string if `pair is relevant to the return value; additional pairs are meaningful only for grouping the regular expression operators. ', and `\|' are operators which respectively match one or more, zero or one, or separate alternatives.Sun OS and other `expr''s treat these as regular characters.
I know it is difficult as old habits die slowly, but this can be done.Recently it was also extended to case conversion using ^^ and ,, digrams This "ksh-originated" group of operators is the most popular and probably the most widely used group of string-handling operators so it makes sense to learn them, if only in order to be able to modify old scripts.that can be used instead in many cases and they are definitely preferable in new scripts that you might write.It will return 4 as the first match for 'd': I recommend using the second one, as this is more compact notation and does not involves using external function expr. # Strings of the form $'xxx' have the standard escaped characters interpreted.It also looks more modern, as if inspired by Python, although its origin has nothing to do with Python. Classic $ # extract substr from pos (0-based) for len $ # replace first match $ # replace all matches $ # replace if matches at beginning (non-greedy) $ # replace if matches at beginning (greedy) $ # replace if matches at end (non-greedy) $ # replace if matches at end (greedy) $ # returns length of $var $ # indirect expansion Double quoted string in shell is almost identical to double quoted string in Perl and performs macro expansion of all variables in it. echo $' Ringing bell 3 times \a \a \a' # May only ring once with certain terminals.
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(POSIX allows either behavior.) For example See shell script - OR in `expr match` - Unix & Linux Stack Exchange for some additional info. In cases when you use if often and need exact position of the substring in the source string you probably will be better off switching to Perl or any other scripting language that you know well. The option -b prints the byte offset of the string shown in the first position that you can extract from the result, but this is a perversion.