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Size: 484
Comment:
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Size: 1289
Comment: `length` is not the only problematic value for a variable argument to `expr`.
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| The fastest way, not requiring external programs (but usable only with ["BASH"] and KornShell): | The fastest way, not requiring external programs (but not usable in Bourne shells): |
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| # POSIX | |
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| or | or for Bourne shells: |
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| # Bourne | |
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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 matching the pattern {{{.*}}}, which is the length of the string.) |
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| or | or: |
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| # Bourne, with GNU expr(1) | |
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| (for a BSD/GNU version of {{{expr}}}. Do not use this, because it is not ["POSIX"]). | (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" }}} ------ 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 |
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
${#varname}or for Bourne shells:
# Bourne expr "$varname" : '.*'
(expr prints the number of characters matching the pattern .*, which is the length of the string.)
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"
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.