Diff for "BashFAQ/007"

Differences between revisions 6 and 8 (spanning 2 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.

A portable way is:

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

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 6 as of 2011-02-28 22:27:41 → 
  Size: 830
  Editor: 203-214-41-227
  Comment: what if $varname == "length" :-(
+   ← Revision 8 as of 2011-03-04 23:01:36 → ⇥
  Size: 1083
  Editor: 203-214-41-227
  Comment: portable (but ugly) expr method suggested in FreeBSD expr page to avoid case where "$varname"=length and using GNU expr :-/
-Deletions are marked like this.
+Additions are marked like this.
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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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+Line 13:
+# Bourne
-Line 20:
+Line 22:
+# Bourne, with GNU expr(1)
-Line 25:
+Line 28:
-This second version is not specified in [[POSIX]], so is not portable across all platforms.
+This second version is not specified in [[POSIX]], so is not portable across all platforms.  However, if {{{$varname}}} expands to {{{"length"}}}, the first version will fail with BSD/GNU {{{expr}}}.
-Line 27:
+Line 30:
-However, if {{{$varname}}} expands to {{{"length"}}}, the first version will fail with BSD/GNU {{{expr}}}.
+A portable way is:
-Line 30:
+Line 33:
+expr \( "X$varname" : ".*" \) - 1
}}}

One may also use `awk`:

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

------

Similar needs:

{{{
# Korn/Bash
-Line 33:
+Line 52:
-Returns the Number of Elements in an Array.
+Returns the number of elements in an array.
-Line 36:
+Line 55:
+# Korn/Bash
-Line 39:
+Line 59:
-Returns the length of the Arrays Element i.
+Returns the length of the array's element i.