Is there a function to return the length of a string?
The fastest way, not requiring external programs (but not usable in Bourne shells):
1 # POSIX
2 "${#varname}"
(note that with bash 3 and above, that's the number of characters, not bytes, which is a significant differences in multi-byte locales. Behaviour of other shells in that regard vary).
or for Bourne shells:
1 # Bourne
2 expr "x$varname" : '.*' - 1
(expr prints the number of characters or bytes matching the pattern .*, which is the length of the string (in bytes for GNU expr). The x is necessary to avoid problems with $varname values that are expr operators)
or:
1 # Bourne, with GNU expr(1)
2 expr length "x$varname" - 1
(BSD/GNU expr only)
This second version is not specified in POSIX, so is not portable across all platforms.
One may also use awk:
1 # Bourne with POSIX awk
2 awk 'BEGIN {print length(ARGV[1])}' "$varname"
(there, whether the length is expressed in bytes or characters depends on the implementation (for instance, it's characters for GNU awk, but bytes for mawk).
Similar needs:
1 # Korn/Bash
2 "${#arrayname[@]}"
Expands to the number of elements in an array.
1 # Korn/Bash
2 "${#arrayname[i]}"
Expands to the length of the array's element i.