Comments on: How To Find BASH Shell Array Length ( number of elements )

By: Dan

Dan — Tue, 03 Jan 2012 22:30:38 +0000

It’s called sharing knowledge. If you don’t like it, move along.

By: Ferk

Ferk — Tue, 03 Jan 2012 20:48:33 +0000

The way it’s done in the post only works when using bash. This is a more POSIX-compatible way of making it work. You can also change the element-separator character to something different than the space, using the variabe IFS.

By: Ryan

Ryan — Mon, 03 Oct 2011 21:48:20 +0000

lol @ all the bikeshedding syntax scholars here. Ok, your voice has been heard, move along idiots.

By: Edward

Edward — Fri, 05 Aug 2011 07:17:39 +0000

1.Write a Linux shell Script to count the Number of user accounts both normal and special or privileged user user accounts on the system.
2.Write an interactive Linux shell script to test whether a file is (a). Read Permission set. (b). Execution permission set (c). Is a non empty file (d). A regular file (e). Ia a directory.

By: Stuart Holme

Stuart Holme — Wed, 27 Oct 2010 15:35:03 +0000

Good points on handling a possibly sparse array, Raymond, but the example is pretty useful if you load the array yourself. Also note that you don’t need to use a variable to store the array length:

for (( i = 0 ; i < ${#my_array[@]} ; i++ )) do; echo "${my_array[i]}"; done

Note the implementations of BASH I am using don't require "$i" as the index of the array, they work fine with just "i". This only seems to work with single character length index variable names though, like "i", not with, for example, "index". YMMV.

Regards,
Stuart

By: Dan

Dan — Wed, 16 Jun 2010 19:39:48 +0000

Here’s a quick flush:
NUM=${#a[@]}; for ((i=0;i<${NUM};i++)); do a[${i}]=''; done

And a for a quick scan, you can do the following either before or after:
COUNT=0; while [ ${COUNT} -lt ${#a[@]} ]; do echo ${a[${COUNT}]}; COUNT=$((COUNT+1)); done

By: Dan

Dan — Wed, 16 Jun 2010 19:29:16 +0000

Well yes, ${#a[@]} pretty much spits out the the number of elements in the array, like the document here said… notice that it’s plainly used as tlen which is the length of the array?

you could do it a million different ways…

NUM=${a[@]}
for ((i=0;i<${NUM};i++)); do echo ${a[${NUM}]}; done

or:

COUNT=0; while [ ${COUNT} -lt ${#a[@]} ]; do echo ${a[${COUNT}]}; COUNT=$((COUNT+1)); done

We could go on and on, since there's more than one way to skin a cat.

By: Dan

Dan — Wed, 16 Jun 2010 17:56:32 +0000

That only works if you have no spaces.

By: Raymond

Raymond — Sat, 07 Feb 2009 10:11:30 +0000

Problems,

a[2]=222
echo ${#a[@]}
1

Thus this is the lenght of the array, not the index of the last element.

Try instead:
for i in “${a[@]}”; do echo $i; done

Some further ideas may be found at
http://tldp.org/LDP/abs/html/arrays.html
http://www.linuxjournal.com/content/bash-arrays

Best Regards,
Raymond

By: budacsik

budacsik — Sat, 20 Sep 2008 12:18:39 +0000

Hi!
I think that this example is bad.
I would do this without a block .

#!/bin/bash

NAMESERVERS=”ns1.nixcraft.net. ns2.nixcraft.net. ns3.nixcraft.net.”
for i in $NAMESERVERS; do
echo “$i”
done

By: those

those — Tue, 05 Aug 2008 20:04:12 +0000

how to clean the array? ;d

By: Diya

Diya — Mon, 28 Jul 2008 08:20:15 +0000

Excellent info.

By: S. Nilesh

S. Nilesh — Sun, 27 Jul 2008 16:47:29 +0000

Nice one ;)