Diff for "BashFAQ/007"

Differences between revisions 4 and 7 (spanning 3 versions)

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 "length", the first version will fail with BSD/GNU expr.

One may also use awk:

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

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

-  ⇤ ← Revision 4 as of 2009-06-09 13:19:16 → 
  Size: 678
  Editor: localhost
  Comment: its about length.. it should also bring examples for arrays
+   ← Revision 7 as of 2011-03-01 00:03:52 → ⇥
  Size: 1014
  Editor: GreyCat
  Comment: Mark which version works where; add awk version; cosmetics
-Deletions are marked like this.
+Additions are marked like this.
 Line 3:
-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
-Line 12:
+Line 13:
+# Bourne
-Line 17:
+Line 19:
-Another one:
+or:
-Line 20:
+Line 22:
+# Bourne, with GNU expr(1)
-Line 23:
+Line 26:
-(This is 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 {{{"length"}}}, the first version will fail with BSD/GNU {{{expr}}}.

One may also use `awk`:
-Line 26:
+Line 33:
+# Bourne
awk -v x="$varname" 'BEGIN {print length(x)}'
}}}

------

Similar needs:

{{{
# Korn/Bash
-Line 29:
+Line 46:
-Returns the Number of Elements in an Array.
+Returns the number of elements in an array.
-Line 32:
+Line 49:
+# Korn/Bash
-Line 35:
+Line 53:
-Returns the length of the Arrays Element i.
+Returns the length of the array's element i.

----
CategoryShell