Execute command from string variable in unix shell script

Question

I have got this code in file scr.sh:

#!/bin/sh
string='ps -e | less'
$string

And when I execute this script it doesn't work. Why? What I should do to execute command from string variable in shell script?

John Kugelman · Accepted Answer · 2014-04-27 19:42:57Z

6

It's better to store commands in functions rather than in variables. Functions are great at it. Variables, not at all.

string() {
    ps -e | less
}

string

You could use eval to execute a command that has redirections (>, <) and pipes (|), but I strongly discourage you from doing so.

eval "$string"    # please don't

answered Apr 27, 2014 at 19:42

John Kugelman

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3 Comments

alvits Over a year ago

Or if it isn't too much to fork then a simple bash -c $string would suffice. Although this method is not as good as a function, it will do the job nonetheless.

alvits Over a year ago

I should also mention, bash -c $string is as bad as eval $string.

dm-kiselev Over a year ago

Why don't use eval? Only it works in this case. Because really I need to read string from keyboard, doing something with it and then execute.

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