关于“”双引号

[root@localhost ~]# shellvar="1111"                        
[root@localhost ~]# echo |awk '{print "in awk:"'$shellvar'}'
in awk:1111

后来才晓得可以用双引号
[root@localhost ~]# echo |awk "{print \"in awk:\"$shellvar}"
in awk:1111
再后来才晓得可以用­-v引入变量
[root@localhost ~]# echo |awk -v a="$shellvar" '{print "in awk:"a}'
in awk:1111
及至可用用eval
[root@localhost ~]# eval "echo |awk  '{print \"in awk:\"$shellvar}'"  
+ eval 'echo |awk  '\''{print "in awk:"1111}'\'''
++ awk '{print "in awk:"1111}'
++ echo
in awk:1111