Diff for "BashFAQ/007"

Is there a function to return the length of a string?

The fastest way, not requiring external programs (but not usable in Bourne shells):

# POSIX
${#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:

# Bourne
expr "$varname" : '.*'

(expr prints the number of characters matching the pattern .*, which is the length of the string (in bytes for GNU expr at least).)

or:

# Bourne, with GNU expr(1)
expr length "$varname"

(BSD/GNU expr only)

This second version is not specified in POSIX, so is not portable across all platforms. However, if $varname expands to any expr operator like + or ( or length, the first version will fail.

A portable way is:

expr \( "X$varname" : ".*" \) - 1

One may also use awk:

# Bourne
awk -v x="$varname" 'BEGIN {print length(x)}'

Though that one will fail for values of $varname that contain backslash characters, so you may prefer:

# Bourne with POSIX awk
awk  'BEGIN {print length(ARGV[1]);exit}' "$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:

# Korn/Bash
${#arrayname[@]}

Returns the number of elements in an array.

# Korn/Bash
${#arrayname[i]}

Returns the length of the array's element i.

CategoryShell