Linux是一个多任务操作系统。这意味着有许多程序同时运行。从用户的角度来看，这意味着你可以同时运行几个程序，而且 bash 肯定有工具，为你控制多个任务的执行。为了能够使用此功能，你需要学习以下命令：
<CTRL> + z- 将当前运行的程序放在后台。jobs- 列出所有后台程序。fg- 把程序带到前台。fg接受一个数字作为参数，它可以从jobs中获取数，或者如果无参数调用，则将最后一个挂起的程序带到前台。ctrl + c- 一次性停止执行当前运行的程序。虽然我不会在这个练习中使用它，但我必须说，这可能是非常有用的。
现在，你将学习如何使用 bash 内置的工具来控制程序的执行。
这样做
1: less -S .profile 2: <CTRL+z> 3: less -S .bashrc 4: <CTRL+z> 5: less -S .bash_history 6: <CTRL+z> 7: jobs 8: fg 9: q 10: fg 11: q 12: fg 13: q 14: fg 15: jobs
你会看到什么
user1@vm1:~$ less -S .profile
# exists.
# see /usr/share/doc/bash/examples/startup-files for
# the files are located in the bash-doc package.
# the default umask is set in /etc/profile; for setti
# for ssh logins,install and configure the libpam-um
#umask 022
# if running bash
if [ -n "$BASH_VERSION" ]; then
# include .bashrc if it exists
if [ -f "$HOME/.bashrc" ]; then
. "$HOME/.bashrc"
[1]+ Stopped less -S .profile
user1@vm1:~$ less -S .bashrc
# for examples
# If not running interactively,don't do anything
[ -z "$PS1" ] && return
# don't put duplicate lines in the history. See bash(
# don't overwrite GNU Midnight Commander's setting of
HISTCONTROL=$HISTCONTROL${HISTCONTROL+:}ignoredups
# ... or force ignoredups and ignorespace
HISTCONTROL=ignoreboth
# append to the history file,don't overwrite it
shopt -s histappend
[2]+ Stopped less -S .bashrc
user1@vm1:~$ less -S .bash_history
echo Hello,$LOGNAME!
echo 'echo Hello,$LOGNAME!' >> .profile
cp .profile .profile.bak
tail .profile
ls -altr
history -w
ls -al
cat .profile
echo Hello,$LOGNAME!' >> .profile
cp .profile .profile.bak
tail .profile
ls -altr
[3]+ Stopped less -S .bash_history
user1@vm1:~$ jobs
[1] Stopped less -S .profile
[2]- Stopped less -S .bashrc
[3]+ Stopped less -S .bash_history
user1@vm1:~$ fg
user1@vm1:~$ fg
user1@vm1:~$ fg
user1@vm1:~$ fg
-bash: fg: current: no such job
user1@vm1:~$ jobs
user1@vm1:~$
