Diff for "BashFAQ/007"

Differences between revisions 5 and 9 (spanning 4 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)}'

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

-  ⇤ ← Revision 5 as of 2009-12-29 17:23:36 → 
  Size: 701
  Editor: MatthiasPopp
  Comment:
+   ← Revision 9 as of 2011-05-26 13:28:27 → ⇥
  Size: 1280
  Editor: sbl-eh4-rp1
  Comment:
-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}}}.

A portable way is:
-Line 26:
+Line 33:
+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
-Line 29:
+Line 59:
-Returns the Number of Elements in an Array.
+Returns the number of elements in an array.
-Line 32:
+Line 62:
+# Korn/Bash
-Line 35:
+Line 66:
-Returns the length of the Arrays Element i.
+Returns the length of the array's element i.