Linux /Unix tr、变量、运算以及终端特性的设置等
使用tr的-s选项去除重复出现的字符：
www.2cto.com
[oracle@localhost tr.folder]$ cat oops.txt
And the cowwwwwws went homeeeee
Or did theyyyyyyyyyyyyy
[oracle@localhost tr.folder]$ tr -s "[a-z]" < oops.txt
And the cows went home
Or did they
删除空行： www.2cto.com
[oracle@localhost tr.folder]$ cat oops.txt
And the cowwwwwws went homeeeee
Or did theyyyyyyyyyyyyy
fas ods css
[oracle@localhost tr.folder]$ tr -s "[\012]" < oops.txt
And the cowwwwwws went homeeeee
Or did theyyyyyyyyyyyyy
fas ods css
转换大小写：
[oracle@localhost tr.folder]$ echo "hello today is a Fine DAY" | tr "[a-z]" "[A-Z]"
HELLO TODAY IS A FINE DAY
删除数字：
[oracle@localhost tr.folder]$ cat oops.txt
And the cowwwwwws went homeeeee
3123asadfas
123ffff
Or did theyyyyyyyyyyyyy
fas ods css
[oracle@localhost tr.folder]$ tr -cs "[a-z][A-Z]" "[\012*]" < oops.txt
And
the
cowwwwwws
went
homeeeee
asadfas
ffff
Or
did
theyyyyyyyyyyyyy
fas
ods
css
[oracle@localhost etc]$ echo "`who | wc -l` users are on today"
2 users are on today
查看当前终端特性：
[oracle@localhost testDir]$ stty -a
speed 38400 baud; rows 44; columns 167; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
lnext = ^V; flush = ^O; min = 1; time = 0;
-parenb -parodd cs8 -hupcl -cstopb cread -clocal -crtscts
isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke
设置styy xxx "xxx"
设置变量的默认值：
[oracle@localhost testDir]$ day=bad
[oracle@localhost testDir]$ echo "today is a ${day:-fine} day"
today is a bad day
[oracle@localhost testDir]$ unset day
[oracle@localhost testDir]$ echo "today is a ${day:-fine} day"
today is a fine day
设置只读变量：
[oracle@localhost testDir]$ readonly
declare -ar BASH_VERSINFO='([0]="3" [1]="1" [2]="17" [3]="1" [4]="release" [5]="i686-redhat-linux-gnu")'
declare -ir EUID="501"
declare -ir PPID="19022"
declare -r SHELLOPTS="braceexpand:emacs:hashall:histexpand:history:interactive-comments:monitor"
declare -ir UID="501"
[oracle@localhost testDir]$ weather=fine
[oracle@localhost testDir]$ readonly weather
[oracle@localhost testDir]$ echo ${weather}
fine
[oracle@localhost testDir]$ weather=fine2
-bash: weather: readonly variable
设置环境变量：
[oracle@localhost testDir]$ console=tty1;export console
[oracle@localhost testDir]$ echo $console
显示所有环境变量：
env
设置终端类型：
[oracle@localhost testDir]$ TERM=linux;export TERM
[oracle@localhost testDir]$ echo $TERM
linux
shell中的运算：
[oracle@localhost testDir]$ var=`date +%Y%m%d`
[oracle@localhost testDir]$ let "var2=$var+1"
[oracle@localhost testDir]$ echo $var2
[oracle@localhost testDir]$ echo $((var2=$var+3))
[oracle@localhost testDir]$ echo var2=$[$var+3]
[oracle@localhost testDir]$ let "var++"
[oracle@localhost testDir]$ echo $var
[oracle@localhost testDir]$ echo $[var+1]
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