Bash Iterate Array Examples

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How do I iterate through an array under Bash scripting?

The Bash shell support one-dimensional array variables. There is no maximum limit on the size of an array, nor any requirement that members be indexed or assigned contiguously. Arrays are indexed using integers and are zero-based.

Creating an array

An array is created automatically if any variable is assigned to using the syntax:

array=( value1 value2 )
users=( www vivek ftp chroot )
ns=( 192.168.1.10 192.168.1.12 )

OR

var[subscript]=value

Accessing subscript

The subscript is treated as an arithmetic expression that must evaluate to a number greater than or equal to zero. You can display values using the following syntax:

echo "${var[0]}"
echo "${ns[0]}"

For Loop Example – Bash Iterate Array

The syntax is as follows:

for var in "${ArrayName[@]}"
do
  echo "${var}"
  # do something on $var
done

Create a shell script as follows:

#!/bin/bash
# define file array
files=(/etc/*.conf)
 
# find total number of files in an array
echo "Total files in array : ${#files[*]}"
total=${#files[*]}
# Print 1st file name
echo "First filename: ${files[0]}"
echo "Second filename: ${files[1]}"
echo "Third filename: ${files[1]}"
# total - 1 = last item (subscript) in an array 
echo "Last filename: ${files[$(( $total-1 ))]}"
 
echo
echo "****************"
echo "*** For Loop ***"
echo "****************"
# Use for loop iterate through an array
# $f stores current value 
for f in "${files[@]}"
do
	echo -n "$f "
done
 
echo
echo 
echo "**************************"
echo "*** C Style For Loop ****"
echo "**************************"
echo 
# Use c style for loop
# get total subscripts in an array
total=${#files[*]}
# 
for (( i=0; i<=$(( $total -1 )); i++ ))
do 
    echo -n "${files[$i]} "
done
 
echo

Sample outputs:

Total files in array : 77
First filename: /etc/aatv.conf
Second filename: /etc/adduser.conf
Third filename: /etc/adduser.conf
Last filename: /etc/xorg.conf

****************
*** For Loop ***
****************
/etc/aatv.conf /etc/adduser.conf /etc/apg.conf /etc/argus.conf /etc/atool.conf /etc/brltty.conf /etc/ca-certificates.conf /etc/chkrootkit.conf /etc/cowpoke.conf /etc/cvs-cron.conf /etc/cvs-pserver.conf /etc/dconf.conf /etc/dconf-custom.conf /etc/debconf.conf /etc/deluser.conf /etc/devscripts.conf /etc/discover.conf /etc/dnsmasq.conf /etc/dnsproxy.conf /etc/e2fsck.conf /etc/fdmount.conf /etc/ffserver.conf /etc/fuse.conf /etc/gai.conf /etc/gssapi_mech.conf /etc/hdparm.conf /etc/hesiod.conf /etc/host.conf /etc/idmapd.conf /etc/inetd.conf /etc/kernel-img.conf /etc/kernel-pkg.conf /etc/krb5.conf /etc/ld.so.conf /etc/lftp.conf /etc/libao.conf /etc/libuser.conf /etc/logrotate.conf /etc/ltrace.conf /etc/mke2fs.conf /etc/mplayerplug-in.conf /etc/mtools.conf /etc/multitail.conf /etc/netscsid.conf /etc/nscd.conf /etc/nsswitch.conf /etc/ntp.conf /etc/pam.conf /etc/pnm2ppa.conf /etc/popularity-contest.conf /etc/pub.rsnapshot.conf /etc/ra.conf /etc/resolv.conf /etc/rsnapshot.bull.conf /etc/rsnapshot.conf /etc/rsnapshot.rose.conf /etc/rsnapshot.txvip.conf /etc/rssh.conf /etc/scrollkeeper.conf /etc/sensors3.conf /etc/sensors.conf /etc/smartd.conf /etc/sysctl.conf /etc/sysfs.conf /etc/syslog.conf /etc/ts.conf /etc/ucf.conf /etc/uniconf.conf /etc/updatedb.conf /etc/usplash.conf /etc/vnc.conf /etc/vsftpd.conf /etc/warnquota.conf /etc/wodim.conf /etc/wpa_supplicant.conf /etc/wvdial.conf /etc/xorg.conf 

**************************
*** C Style For Loop ****
**************************

/etc/aatv.conf /etc/adduser.conf /etc/apg.conf /etc/argus.conf /etc/atool.conf /etc/brltty.conf /etc/ca-certificates.conf /etc/chkrootkit.conf /etc/cowpoke.conf /etc/cvs-cron.conf /etc/cvs-pserver.conf /etc/dconf.conf /etc/dconf-custom.conf /etc/debconf.conf /etc/deluser.conf /etc/devscripts.conf /etc/discover.conf /etc/dnsmasq.conf /etc/dnsproxy.conf /etc/e2fsck.conf /etc/fdmount.conf /etc/ffserver.conf /etc/fuse.conf /etc/gai.conf /etc/gssapi_mech.conf /etc/hdparm.conf /etc/hesiod.conf /etc/host.conf /etc/idmapd.conf /etc/inetd.conf /etc/kernel-img.conf /etc/kernel-pkg.conf /etc/krb5.conf /etc/ld.so.conf /etc/lftp.conf /etc/libao.conf /etc/libuser.conf /etc/logrotate.conf /etc/ltrace.conf /etc/mke2fs.conf /etc/mplayerplug-in.conf /etc/mtools.conf /etc/multitail.conf /etc/netscsid.conf /etc/nscd.conf /etc/nsswitch.conf /etc/ntp.conf /etc/pam.conf /etc/pnm2ppa.conf /etc/popularity-contest.conf /etc/pub.rsnapshot.conf /etc/ra.conf /etc/resolv.conf /etc/rsnapshot.bull.conf /etc/rsnapshot.conf /etc/rsnapshot.rose.conf /etc/rsnapshot.txvip.conf /etc/rssh.conf /etc/scrollkeeper.conf /etc/sensors3.conf /etc/sensors.conf /etc/smartd.conf /etc/sysctl.conf /etc/sysfs.conf /etc/syslog.conf /etc/ts.conf /etc/ucf.conf /etc/uniconf.conf /etc/updatedb.conf /etc/usplash.conf /etc/vnc.conf /etc/vsftpd.conf /etc/warnquota.conf /etc/wodim.conf /etc/wpa_supplicant.conf /etc/wvdial.conf /etc/xorg.conf 

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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