[root@BASE ~]# cat c.txt

aa

    ccc

bbb    bbbb

[root@BASE ~]# cat c.txt|tr -s " "            //删除连续重复的空格只保留一个

aa

 ccc

bbb bbbb

[root@BASE ~]# cat c.txt|tr -s " ","a","c","b"           //删除重复的空格，a，b，c只保留一个

a

 c

b b

[root@BASE ~]# cat c.txt|tr -s " " "k"         //删除重复的空格只保留一个，并且将空格替换成“k”

aa

k

kccc

bbbkbbbb

[root@BASE ~]# cat c.txt|tr -d " "           //删除空格

aa

ccc

bbbbbbb

[root@BASE ~]# cat c.txt|tr -d "aaa"         

    ccc

bbb    bbbb

[root@BASE ~]# cat c.txt|tr -d "a"  

    ccc

bbb    bbbb

[root@BASE ~]#