Diff for "BashFAQ/007"

Differences between revisions 1 and 8 (spanning 7 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 1 as of 2007-05-02 22:51:12 → 
  Size: 484
  Editor: redondos
  Comment:
+   ← 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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-[[Anchor(faq7)]]
+<<Anchor(faq7)>>
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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 10:
-or
+or for Bourne shells:
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+Line 13:
+# Bourne
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+Line 17:
-({{{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.)
-Line 16:
+Line 19:
-or
+or:
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+# Bourne, with GNU expr(1)
-Line 22:
+Line 26:
-(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:

{{{
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