Shell Programming and Scripting

 
 
-bash-3.00$ abc=deepak
-bash-3.00$ a=1
-bash-3.00$ def_${a}=$abc
-bash: def_1=deepak: command not found

eval def_${a}=$abc

-bash-3.00$ abc=deepak
-bash-3.00$ a=1
-bash-3.00$ eval def_${a}=${abc}
-bash-3.00$ echo ${def_${a}}
-bash: ${def_${a}}: bad substitution

-bash-3.00$ abc=deepak
-bash-3.00$ a=1
-bash-3.00$ eval def_${a}=${abc}
-bash-3.00$ echo ${def_${a}}
-bash: ${def_${a}}: bad substitution

$ abc=deepak
$ a=1
$ eval def_${a}=${abc}

$  eval echo \${def_${a}}
deepak
$

$ vname=def_${a}
$ eval echo \${${vname}}
deepak
$

$ vname=def_${a}
$ echo ${!vname}
deepak
$