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eval - Unix, Linux Command
NAME
eval - Eval is a built in linux or unix command.
SYNOPSIS
eval [arg ..]
DESCRIPTION
eval is a built in linux or unix command. The eval command is used to execute the arguments as a shell command on unix or linux system. Eval command comes in handy when you have a unix or linux command stored in a variable and you want to execute that command stored in the string. The eval command first evaluates the argument and then runs the command stored in the argument.
EXAMPLES
Example-1:
To execute that command stored in the string:
$ COMMAND="ls -lrt"
$ eval $COMMAND
output:
total 16 -rw-rw-r-- 1 user group 11 Oct 4 01:06 sample.sh
-rw-rw-r-- 1 user group 0 Oct 4 01:06 test.bat -rw-rw-r-- 1 user group 0 Oct 4 01:06 xyz_ip
Example-2:
To print the value of variable which is again variable with value assigned to it
$ a=10
$ b=a
$ c='$'$b ( note: The dollar sign must be escaped with '$'
)
$ echo $c
output:
$a
$ eval c='$'$b
$ echo $c
output:
10
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