Diff for "BashFAQ/007"

Differences between revisions 4 and 16 (spanning 12 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):

   1 # POSIX
   2 "${#varname}"

(note that with bash 3 and above, that's the number of characters, not bytes, which is a significant differences in multi-byte locales. Behaviour of other shells in that regard vary).

or for Bourne shells:

   1 # Bourne
   2 expr "x$varname" : '.*' - 1

(expr prints the number of characters or bytes matching the pattern .*, which is the length of the string (in bytes for GNU expr). The x is necessary to avoid problems with $varname values that are expr operators)

or:

   1 # Bourne, with GNU expr(1)
   2 expr length "x$varname" - 1

(BSD/GNU expr only)

This second version is not specified in POSIX, so is not portable across all platforms.

One may also use awk:

   1 # Bourne with POSIX awk
   2 awk  'BEGIN {print length(ARGV[1])}' "$varname"

(there, whether the length is expressed in bytes or characters depends on the implementation (for instance, it's characters for GNU awk, but bytes for mawk).

Similar needs:

   1 # Korn/Bash
   2 "${#arrayname[@]}"

Expands to the number of elements in an array.

   1 # Korn/Bash
   2 "${#arrayname[i]}"

Expands to 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 16 as of 2015-03-05 00:24:26 → ⇥
  Size: 1522
  Editor: izabera
  Comment: syntax hl
-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):
 Line 5:
-{{{
${#varname}
+{{{#!highlight bash
# POSIX
"${#varname}"
-Line 8:
+Line 9:
+(note that with `bash` 3 and above, that's the number of characters, not bytes, which is a significant differences in multi-byte locales. Behaviour of other shells in that regard vary).
-Line 11:
+Line 14:
-{{{
expr "$varname" : '.*'
+{{{#!highlight bash
# Bourne
expr "x$varname" : '.*' - 1
-Line 15:
+Line 19:
-({{{expr}}} prints the number of characters matching the pattern {{{.*}}}, which is the length of the string.)
+({{{expr}}} prints the number of characters or bytes matching the pattern {{{.*}}}, which is the length of the string (in bytes for GNU `expr`). The `x` is necessary to avoid problems with `$varname` values that are `expr` operators)
-Line 17:
+Line 21:
-Another one:
+or:
-Line 19:
+Line 23:
-{{{
expr length "$varname"
+{{{#!highlight bash
# Bourne, with GNU expr(1)
expr length "x$varname" - 1
-Line 23:
+Line 28:
-(This is for a BSD/GNU version of {{{expr}}}. Do not use this, because it is not [[POSIX]]).
+(BSD/GNU {{{expr}}} only)
-Line 25:
+Line 30:
-{{{
${#arrayname[@]}
+This second version is not specified in [[POSIX]], so is not portable across all platforms.

One may also use `awk`:

{{{#!highlight bash
# Bourne with POSIX awk
awk  'BEGIN {print length(ARGV[1])}' "$varname"
-Line 29:
+Line 39:
-Returns the Number of Elements in an Array.
+(there, whether the length is expressed in bytes or characters depends on the implementation (for instance, it's ''characters'' for GNU awk, but ''bytes'' for `mawk`).
------
-Line 31:
+Line 42:
-{{{
${#arrayname[i]}
+Similar needs:

{{{#!highlight bash
# Korn/Bash
"${#arrayname[@]}"
-Line 35:
+Line 49:
-Returns the length of the Arrays Element i.
+Expands to the number of elements in an array.

{{{#!highlight bash
# Korn/Bash
"${#arrayname[i]}"
}}}

Expands to the length of the array's element i.

----
CategoryShell