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Comment: Mark which version works where; add awk version; cosmetics
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| (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). |
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| ({{{expr}}} prints the number of characters matching the pattern {{{.*}}}, which is the length of the string.) | ({{{expr}}} prints the number of characters or bytes matching the pattern {{{.*}}}, which is the length of the string (in bytes for GNU `expr`).) |
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| This second version is not specified in [[POSIX]], so is not portable across all platforms. However, if {{{$varname}}} expands to {{{"length"}}}, the first version will fail with BSD/GNU {{{expr}}}. | This second version is not specified in [[POSIX]], so is not portable across all platforms. However, if {{{$varname}}} expands to any `expr` operator like `+` or `(` or `length`, the first version will fail. A portable way is: {{{ expr \( "X$varname" : ".*" \) - 1 }}} |
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| 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`). |
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 or bytes matching the pattern .*, which is the length of the string (in bytes for GNU expr).)
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.