How Linux Works

Command Substitution

The Bourne shell can redirect a command's standard output back to the shell's own command line. That is, you can use a command's output as an argument to another command, or you can store the command output in a shell variable. You do this by enclosing a command in backquotes (').

Here's an example that stores a command inside a variable, FLAGS:

#!/bin/sh
FLAGS='grep ^flags /proc/cpuinfo | sed 's/.*://' | head −1'
echo Your processor supports:
for f in $FLAGS; do
    case $f in
        fpu)    MSG="floating point unit"
                ;;
        3dnow)  MSG="3DNOW graphics extensions"
                ;;
        mtrr)   MSG="memory type range register"
                ;;
        *)      MSG="unknown"
                ;;
    esac
    echo $f: $MSG
done

The second line contains the command substitution, in bold type. This example is somewhat complicated, ...