use text and use as command?

问题

i whant to build a script to extract the word from a file in a command:

for example: in my file i keep my username , how can i export the username without knowing the username as part of my command , which my command is : suspend here should be the word exported?

From my file which has the text inside "JOHN" how can i tell the command : suspend that the username is JOHN ?

how can i cat/grep/sed the text from the file as part of command :

something like suspend |cat file , i have try that but the suspend command does not take the username , so there should be something different .

my ideea where like this

#!/bin/sh
username=cat my-file;

suspend $username ,

but i had no succes , because my $username is not display from the cat , the cat is shows it but thats all that is doing.

回答1:

Use the following syntax

  username=$(cat my-file)

you might also use backquotes like

  username=`cat my-file`

but the $(...) notation is preferable: it can be nested and is more readable.

Please read the Advanced Bash Scripting Guide (it will teach you a lot, even if it can be criticized)

Your usage of suspend is incorrect, and I don't understand what you want to do with it. What would suspending a user mean to you? Perhaps you want to use pgrep or pkill (to kill all the processes of that user, which I feel is too harsh)...?

回答2:

The command to read a line is, shockingly, named "read":

$ cat file
John
$ IFS= read -r username < file
$ echo "$username"
John

"cat" is the command to concatenate files.

Setting IFS= and using the -r arg to read are so that read handles leading white space and/or backslashes as-is rather then interpreting them. If you KNOW your file can never contain those or you want read to strip leading white space and/or interpret backslashes than you can get rid of those.

来源：https://stackoverflow.com/questions/17714810/use-text-and-use-as-command